Sciences Subject (BS11001)

151 Cosmetic products ‟lipstick and facial powder. Topic 3 How to choose and use substances safely There are both pros and cons to substances that we use in everyday life. Therefore, before starting to use any substance, we must consider the following: 1.Product label: It is essential to study and understand details that are stated on the product label before buying or using any substance. The expiry date of the product, particularly food products must be checked and the consumer must strictly follow the instruction on the label as well. 2. Use an appropriate amount of the substance: Some substances can be harmful if used excessively. 3. The disposal of used containers must be carried out appropriately such as containers of toxic substances shall not be disposed of in a canal or river, etc When using any substances, we need to consider safety as well. Some substances such as insecticides or pesticides will be harmful to the user’s health if over used. If toxic substances are left over in fruit or vegetable, it will be harmful to consumers. Moreover, substances that we use may affect the environment such as waste water discharged into the

152 river may cause foul water, etc. Therefore, before we use substances in everyday life we should study in detail about how to use, keep and dispose of them in order to prevent against any danger that may occur to human beings and impact the environment. Activity Using substances safely Part 1 Survey 5 kinds of substance used in everyday life and record the result. Substance names Types Directions for use 1. 2. 3. 4. 5. 2.Tell at least 3 ways to safely use substances. 1…………………………………………………………………………………………………. 2…………………………………………………………………………………………………. 3………………………………………………………………………………………………….

153 3. How do substances used in everyday life affect human beings and the environment? 1…………………………………………………………………………………………………. 2…………………………………………………………………………………………………. 3………………………………………………………………………………………………….

154 Lesson 10 Force and its movement Main learning essence Definition and types of force, force resulting from the work of force, pressure, buoyancy, gravity, friction, use of force and its movement in everyday life. Expected learning outcome 1. Be able to explain the types of force, force resulting from the work of force, pressure, buoyancy, gravity and friction. 2. Be able to use force and its movement for the benefit of everyday life. Scope Topic 1 Force and movement of force Topic 2 Pressure Topic 3 Gravity; definition, pros and cons of gravity

155 Topic 1 Force and movement of force Force is an externally applied power which can change the status of an object such as making an object move from a state of rest, making a moving object move faster or slower, making a moving object change its direction and making an object change its size or shape. Force is a vector quantity which has both a magnitude and a direction. Therefore, any addition or subtraction of force must be done following the rule of vectors. Types of force: There are various types of force, i.e. subdivide force, net force, action and reaction, parallel force, couple, tensile, centrifugal force, resistance and friction. Friction Force is the force induced by friction between the surface of two objects that are moving or attempting to move. Friction is the force that resists movement of an object and always is in the opposite direction to the object’s moving direction. There are two types of friction, i.e. 1. Static friction, a friction that occurs when an object starts moving. 2. Kinetic friction, a friction that occurs while an object is moving. Factors affecting friction 1. Weight of the object: An object with more weight on the surface will have more friction than an object which is lighter. 2. Exposed surface: A smooth surface has less friction than a rough surface. Pros of friction 1. Prevents car accidents. 2. Prevents a shoe fall. Cons of friction If car wheels and road surfaces have a high friction, the car will run slowly and increased fuel consumption is required to enable the car to have enough power to overcome friction. . When moving a big cabinet, if we push the cabinet we will find that the cabinet is hard to move because of friction. It is necessary, therefore, either to push the cabinet harder or to lessen friction by putting a piece of cloth under the cabinet’s legs and then push at a constant speed. Gravitational force is the force that is caused by the earth’s mass. The gravity has an effect on all substances, even those as small as an atom or as big as the earth itself or even

156 as big as a galaxy. Therefore, all substances or masses will always have a gravitational force that makes them attracted to each other such as the gravity that has an effect on all humans beings on earth. Buoyancy is a resultant force acting on the surface of a partly or wholly immersed object. It is an uplifting reaction acting to oppose the weight of an object that is sinking due to the gravity of the earth. The buoyancy is equal to the weight of the fluid the quantity of which is equal to the immersed part of the object which can be proven by examining the immersed object in the fluid. Buoyancy equals to the weight of the fluid which is replaced by the immersed object. Factors affecting buoyancy are as follows: 1. Oobject type: Objects have different densities. Objects with a higher density will sink deeper into the fluid. 2. Fluid type: Fluids with a higher density will have a higher buoyancy. 3. Object size: Size has an effect on the fluid volume of the immersed object. When there is more volume of the replaced fluid, buoyancy will be greater. Pros of buoyancy It is used in shipbuilding to prevent ships from sinking. The gravity of earth, meaning pros and cons of the gravity. Gravity is an adhesive force between the mass of the earth and objects on earth. It enables everything stay on the surface of the earth by always having the center of gravity perpendicular to the earth’s surface. The Law of Gravitation Newton discovered this theory by accident. An incident leading to the discovery of this theory happened the day when Newton was observing the moon and he was curious as to why the moon should orbit around the earth. While he was looking at the moon, he heard the sound of an apple falling to the ground. When he saw this, he started to think about why why objects must always fall on the ground instead of floating up in the sky. He then thought that there must be some kind of force that makes apples fall to the ground. From this curiosity, Newton started to do experiments on the earth’s gravity. The first experiment of Newton was to tie a stone on a rope and swing it around himself. He concluded that the

157 rope is the main cause which prevents the swinging stone from being thrown away. Ttherefore, the reason why planets and the earth orbit around the sun and why the moon orbits around the earth is due to the gravitational force of the sun that has an action on the earth and the planets as well as the gravitational force of the earth that has an action on the moon. The reason why apples fall to the ground is also due to the gravity of the earth. Pros of the gravitational force There are pros which are direct and indirect as follows: 1. The gravity of the earth prevents objects on earth from flying away from the earth, especially preventing the atmosphere that envelops the earth from floating into space so that human can live on the earth. 2. The gravity of the earth makes rain fall on the ground and thus provide moisture to living things on the earth. 3. The gravity of the earth makes water flow from a higher point to a lower point. This makes waterfalls and makes water in rivers flow to the sea. Human beings use the benefits from water flows extensively such as the building of dams to generate electricity from hydropower, etc. When force is applied to an object, 3 effects may occur as follows: 1. A static object may start moving. 2. The velocity of a moving object may change. 3. The moving direction of an object may change. Newton’s Law of Motion has 3 rules as follows: 1. An object will stand still or move at a constant speed if the summation of force (Resultant force) applied to the object equals to zero. 2. When a resultant force which is not equal to zero acts on an object, the object with a mass will move with acceleration and the size of force shall be equal to mass multiplied by acceleration. 3. Every force always has an equal reaction in the opposite direction. Benefits provided by the gravity of the earth are enormous. Imagine what would happen if the earth were without gravity. It would be correct to say that everything, even the earth itself would perish. Examples of how human beings use both the direct and indirect benefits of the earth’s gravity are as follows:.

158 1. The gravity of the earth prevents objects from flying away out of the earth. Especially, it prevents the atmosphere that envelops the earth from flying away into space and thus enable human beings to be able to live on this tearth. 2. The gravity of the earth makes rain fall on the earth and thus provides moisture to all living things on the earth. 3. The gravity of the earth makes water flow from a higher point to a lower point, creating waterfalls, the flowing of water from rivers into the sea. Human beings use the benefits of flowing water enormously such as for the building of dams to generate electricity from hydro power. 4. The gravity of the earth enables all objects to have a weight. 5. The gravity of the earth makes clothes dry faster. While clothes are hung to dry, sunshine makes water in the clothes evaporate and gravity makes water drip on the ground.

159 Activity Study and do research on the definitions and provide examples of the following forces: 1. Subdivide force 2. Resultant force 3. Action and reaction 4. Parallel force 5. Couple force 6. Tensile 7. Centrifugal force 8. Resistance

160 Topic 2 Pressure Definition Pressure is the force (force F) per unit of an area (area A) In the SI system, a unit of pressure is measured in Pascal (Pa) or Newton per square meter ( ) or kilogram per meter per second square ( ). For pressure in the unit of Mercury millimeter (mmHg) given that 760 mmHg = 101325 Pascal or 1 atm = 101325 Pa = 101.325 Pressure or air pressure acting on the surface of the earth is called atmospheric pressure. It is commonly known that fluid also has a pressure. Fluid pressure depends on 3 factors which are depth or height, density of the fluid and gravity of the earth. The measurement of the atmospheric pressure may be conducted using an instrument called Barometer. The inventor of the world’s first barometer is an Italian mathematician named Torricelli in AD 1643. The instrument consists of a mercury filled bowl and a glass tube fully filled with mercury turned upside down in the mercury bowl as shown in the picture below (Mercury is a substance which is fluid at room temperature. The density of mercury equals 13.4 g/ml). Pressure in the fluid In the study of fluid pressure, it was found that when filling a punctured plastic bottle with water, the water will jet out in directions indicated by arrows as shown in Figure 1. Therefore, it is shown that there is a force that acts on water in the bottle and this force pushes water out in directions perpendicular to the surface of the container regardless of the location. We call the force in the fluid that is perpendicular to a unit of container surface “fluid pressure”

161 Figure 1 Illustration of water pressure at various locations of the bottle. Characteristic of fluid pressure can be summarized as follows: 1. Fluid in a container will push against the surface of the container in all directions and will always be perpendicular to the container surface. 2. Every point in the fluid will have a pressure on them in all directions. Figure 2 shows the various directions that fluid pressure exercises on the surface of the container and on immersed objects 3. For similar fluid, pressure increases with more depth and at equal depth, fluid levels will be equal. 4. In different fluids at an equal depth, fluid pressure depends on fluid density. It can be concluded that “For a static fluid at a given temperature, fluid pressure always has a direct variation linked to depth and density of the fluid” (not depending on the container shape or fluid volume) In the study of fluid pressure, it was found that when piercing sizeable holes in plastic water bottles, water will jet out off the puncture. This situation shows that there is an acting force on water in the container and therefore, when the container has punctures the pressure will push water to jet out of the puncture always in a perpendicular direction to the

162 puncture. We call the force in the fluid that acts in perpendicular to a surface area unit of the container as fluid pressure. Properties of fluid pressure At any point in the fluid, there is an acting force in all directions due to fluid. 1. If we examine the surface of a container, force of the fluid will always act in a perpendicular direction to the container surface. 2. For atmospheric pressure, it is called absolute pressure (pressure that always has a constant force) 3. Pressure at any point in the fluid which is generated from a weight on the fluid is in direct variation to the depth and density of the fluid when the fluid is static and is at a constant temperature. 4. Pressure in a particular type of fluid does not depend on the volume or shape of the container. „ Because pressure depends on the height and density of the fluid. Assuming that the types of fluid in the containers are similar (thus having similar density) and the height of the fluids are also similar. All of the containers will have an equal pressure at the bottom as shown in the figure but the force acting on the bottom of the containers will be different due to the difference of fluid weight. „ Therefore, at different heights, pressure at different depths will be different regardless of the shape of the container. Gas volume and gas pressure Air pressure is a force acting on the surface of the earth due to the weight of air at any point which is taken as a stalk of atmosphere from the ground to the end of the atmosphere. Relationship between air pressure and height from the sea level is as follows: 1. At a similar height, air will have an equal pressure. This principle is used in construction tools used to measure levelness. 2. At an increasing height, pressure and density of air decrease. This principle is used in instruments for measuring the altitude which is called Altimeter.

163 3. “For every 11 meters which is added to the sea level, the mercury level will decrease by 1 millimeter mercury and for every 11 meters which is added to the depth of the sea level, the mercury level will increase by 1 millimeter” 4. Pressure of the air at sea level is called a pressure of 1 atmosphere. 5. There are 2 ways to measure air pressure, i.e. measured by the height of water and by the height of mercury.

164 Lesson 11 Energy in Everyday Life and Energy Conservation Main learning essence The gain knowledge about the meaning and significance of energy, types of energy in everyday life, household electricity, building basic electric circuits, energy saving, forces and property of forces, natural phenomena involving light, sound, sound property, noise pollution, and alternative energy in everyday life. Expected learning outcome 1. Be able to explain and identify types of energy related to everyday life 2. Be able to explain how to use electricity in homes and how to build basic electric circuits 3. Be able to specify how to save and conserve energy 4. Be able to identify light properties and natural phenomena involving light 5. Be able to describe sound property and noise pollution prevention 6. Be able to identify qualifications and types of alternative energy in everyday life Content scope Topic 1: Electrical energy Topic 2: Light energy Topic 3: Sound energy

165 Topic 1: Electrical energy Energy is the capacity to work and can be classified into 2 major forms - usable energy and stored energy. Usable energy includes electrical energy, light energy, and sound energy. Stored energy consists of chemical energy (energy which is stored in a substance), nuclear energy (energy stored in an element), and potential energy (energy which is stored in an object as a result of its position). Potential energy can be divided into gravitational potential energy and elastic potential energy. Electrical energy Electrical energy refers to a form of energy which can be converted into another form of energy. Electrical energy can be generated from various sources. To use electrical energy, the energy source must be connected with an electric circuit through which the electrical energy can travel and be changed into other forms of energy such as mechanical energy, heat energy, sound energy and light energy. 2.1 Source of electrical energy Source of electrical energy produces electrical current which flows into and powers an electrical device through an electric circuit. Electrical energy can be generated through various means and sources: 1. Friction ‟ Rubbing different materials together will generate a type of power which can attract light, thin objects. The rubbed objects will become charged and the power created is called static electricity. However, the effect is temporary. 2. Chemical reaction ‟ As a result of chemical reaction, chemical energy will transfer through conductors and change into electrical energy. This energy production principle is used for dry battery and automobile battery. 3. Magnetic field ‟ Rotating or moving a coil of wires in a magnetic field will create voltage in the coil. This concept applies to the invention of a dynamo which can generate both direct current and alternating current.

166 4. Pressure ‟ Some types of minerals can generate electrical energy when high pressure is constantly applied to them. These minerals are used for producing microphones and phono cartridges, etc. 5. Animal – Some animals such as electric eels have organs that produce electricity and can generate electric shocks. 6. Heat ‟ Burning metals can also generate electricity. 2.2 Energy conversion Generally, energy can be converted from its original form into another form. Home electrical appliances can convert electrical energy into another type of energy such as light energy, heat energy, mechanical energy and sound energy or multiple types of energy at the same time. 1. Conversion into light energy ‟ Light bulbs can change electrical energy into light energy and can be divided into 2 types: 1.1 Incandescent lamp - Incandescent lamp is a bulb-shaped glass filled with nitrogen and argon. Each bulb has a filament wire inside which is, nowadays, made of tungsten and osmium. When a filament wire is heated to a high temperature by an electric current passing through it, the filament wire which has high heat-resistance will glow. 1.2 Fluorescent light lamp ‟ It is sometimes called a “neon lamp” and comes in different shapes. The lamp is vacuum and contains a slight amount of mercury vapor and phosphor coating inside. When electricity passes the mercury vapor, mercury atoms will emit ultraviolet light which causes the phosphor coating to produce visible light. At present,

167 fluorescent light lamp is available in many different designs and sizes such as compact fluorescent lamp which is effective in energy saving. Compact fluorescent lamps 2. Conversion into heat energy ‟ Heat-producing electrical appliances have a resistance coil or a heating coil as their key element. The coil is generally made of nichrome. When electric current passes through this element, the heat is generated. Electrical appliances which change electricity into heat energy include, for example, electric irons, electric rice cookers, electric kettles, toasters and hair dryers. Heat-producing electrical appliances 3. Conversion into mechanical energy ‟ A motor is an electrical device which produces mechanical energy. A motor has a dynamo as its major element but they work differently as a motor changes electrical energy into mechanical energy. Electrical

168 appliances having electrical motors are fans, blenders, vacuum cleaners, VCD players, refrigerators, air-conditioners, laundry machines, etc. 4. Conversion into sound energy ‟ There are a large number of electrical appliances which can produce sound energy such as radios, recorders and amplifiers. 2.3 Household electricity and basic electric circuits Electric circuit means a path for electric current to flow from an energy source to an electrical appliance and then back to the energy source. Generally, household electric circuits are parallel circuits which place each electrical device in its own separate branch. So, if an electrical device is not working properly for any reason, other electrical devices will not be affected because they are not on the same circuit. Alternating current electricity with the potential difference of 220 volts is the type of electricity commonly used in homes. Residential electrical service uses a 2-wire system: 1. Neutral wire or N wire which has zero electric potential 2. Live wire or L wire which has an electric potential of 220 volts. Typically, L and N wires are connected to an electrical panel which systematically controls electricity distribution in a home. An electrical panel commonly has a main fuse, a main circuit breaker, and branch circuit breakers which control electricity supply at specific zones of a home such as a lower floor, an upper floor or a kitchen. Wires from meter Circuit breaker Fuse Upper Lower Kitchen floor floor Picture 1: Sample of a household circuit

169 Household electricity flows through the L wire, then circuit breakers, fuses and switches into electrical appliances before it returns through the neutral wire as shown below: Main circuit breaker Radio Laundry machine Socket Fuse Bulb Meter Branch circuit breaker Main electrical panel Socket Picture 2: Household electricity circuit Electric circuit equipment Electrical devices are comfort appliances which can easily change electrical energy into other forms of energy. Electrical devices commonly used in homes are electric irons, electric rice cookers, fans, light bulbs, laundry machines, etc. Apart from these electrical appliances, other equipment such as electricity wires, fuses, switches, sockets and plugs is also necessary for the household electricity circuit. Electrical cable - Electrical cable is an equipment for transferring electrical power from one point to another point. Current runs along an electric cable carrying electricity to an electrical appliance. Electric cables made of conducting materials (materials which permit a flow of electric charge) are: 1. High voltage cable ‟ It uses aluminum which is cheaper and lighter than copper as a conductor. 2. General cable (for home use) ‟ It uses copper which is cheaper than silver as a conductor. Fuse - It provides overcurrent protection by automatically breaking the circuit of electricity when there is an excessive current. Fuse is made of an alloy composed of lead, tin and bismuth. Fuse has a low melting point and a high resistance. There are various types of fuses to serve different purposes.

170 Fuse wire Blade fuse Ceramic fuse Cartridge fuse Picture 3: Different types of fuses Switch - It is a device for connecting and breaking an electrical circuit at a specific spot. Its function is similar to the function of a circuit breaker. The switch is connected in series with an electrical appliance. There are 2 switch types: single-throw and double-throw. Circuit 1 Circuit 2 Picture 4: Switch types Circuit breaker - It is a device for interrupting or connecting all electrical circuits in a house. It has a frame and a lever which has an insulated handle and 2 strips of metal. When the lever is down, electric current flows from a meter to an electric circuit. Pushing the lever up will stop the current flow.

171 Insulator Conductor Fuse Picture 5: Circuit breaker and fuse in a circuit breaker 2.4 Electrical safety at home Electricity can be dangerous if used incorrectly and direct contact with electric current can be deadly. It is advisable to be careful when using electricity. As electric current cannot pass through insulators, we use insulators to prevent electric shock. To avoid dangers of electricity, the following electrical safety rules should be followed: 1. Electrical cables must be insulated and regularly checked. 2. Do not touch any electrical appliances with wet hands because our body's water content is a conductor of electricity. 3. Always unplug electrical appliances after use. 4. Do not climb any power pole or fly kites near power lines. 5. Stay far away from broken and fallen power lines. 6. Keep electrical cables away from fuels to avoid damage. 7. Do not plug fingers or stuff into power sockets. 8. Use correct fuse size. Do not use a fuse that is too small. 9. Do not plug in too many electrical appliances in one socket. 10. Turn off and unplug televisions during a storm. 11. Do not use electrical appliances with broken cords or frayed insulators. 12. Do not get close to areas with the \"high voltage\" sign.

172 2.5 Electricity saving 1. Turn off lights and electrical appliances after use. 2. Buy energy-efficient appliances and check energy rating label before making a purchase decision. 3. Switch off the air conditioner when you are not in a room for more than 1 hour. 4. Regularly clean air conditioner filters to reduce air conditioner's energy consumption. 5. Set the temperature of the air conditioner to 25 degrees Celsius which is a comfortable temperature. Each degree lower will consume 5% more energy. 6. Make sure the air-conditioned room is tightly closed to prevent cool air from escaping from the room. 7. Avoid storing documents or items in an air-conditioned room in order to reduce energy consumption. 8. Use heat-insulating materials for air-conditioned areas to reduce energy waste caused by heat transfer. 9. Plant trees near the building as a big tree has a cooling effect of a 1-ton air conditioner or around 12,000 BTUs. 10. Buy electric fans with quality certification label. Low-quality electric fans become broken easily. 11. Use electric fans instead of the air conditioner when the weather is not too hot. 12. Use energy-saving lamps, compact fluorescent lamps or fluorescent lamps instead of incandescent lamps. 13. Use electronic ballasts with compact fluorescent lamps to save even more energy. 14. Use luminaires with a reflector to maximize efficiency. 15. Regularly clean the surfaces of light bulbs at least 4 times a year to increase brightness. 16. Paint buildings with light colors for better light reflection and brightness. 17. Use natural lighting wherever possible. 18. Do not leave the refrigerator's door open. Regularly clean the refrigerator's coil and interior.

173 19. Do not spray too much water on clothes to be ironed. 20. Unplug the iron a few minutes before finishing ironing and complete the ironing on stored energy. 21. Complete ironing without interruptions to avoid turning irons on and off several times. 22. Do not leave a television on when nobody is watching it to avoid a waste of energy. 23. Use a gas stove instead of an electric stove. 24. Do not leave the rice cooker plugged because it is a waste of energy. The warm mode will be activated while the rice cooker is plugged. 25. Unplug electric kettles after use. 26. Control each lamp by a separate switch to avoid energy waste. Do not use a single switch to control all lights on the same floor. 27. Do not use heat-generating appliances such as electric kettles or electric pots in air-conditioned rooms. 28. Regularly maintain and clean electrical appliances to keep them in a good condition and use less energy.

174 Topic 2: Light energy Light is a form of energy which can be transformed into other energy forms. Light makes things visible. Light is a ray and, like a wave, travels in a straight line from sources through a medium which can be divided into 3 groups: 1. Translucent medium mean objects which allow some light to pass through such as fog and dirty water. 2. Transparent medium mean objects which light can pass through easily such as clear water and air. 3. Opaque medium mean objects which no light can pass through such as tiles and mirrors. 3.1 Source of light It means materials which originate light. Light sources can be divided into 2 groups: 1. Natural light sources ‟ Examples are the sun, stars, fireflies and some types of sea fish. 2. Artificial light sources ‟ Humans have invented artificial light sources to create light for use at nights when the Earth does not get light from the sun. Examples of artificial sources of light are light bulbs, lamps and candles. The biggest source of light on the Earth is the Sun which radiates energy in various forms to the Earth. Light is a type of energy which the Earth receives from the Sun. 3.2 Property of light Light is very important for lives. It helps us see things around us. However, our vision is affected by the property of light. 1. Reflection of light This is an important property of light which is related to the travel of light to an object surface. The direction which light travels through the air to the object surface is called the incident ray while the direction which the reflected light travels from the object surface into the air is called the reflected ray. These 2 rays are on different sides of a straight line called the normal line which is drawn perpendicular to the object surface, starting at the point where the light falls and reflects.

175 Rays reflect in one direction Rays reflect in different directions Picture 6: Light reflection Light reflection on a flat surface (top) Light reflection on an uneven surface (bottom) In addition, there are 2 important angles created between the incident ray, the reflected ray and the normal line. They are the angle of incidence (θi) and the angle of reflection (θr). The measurement of the angle of incidence and the angle of reflection reveals that “if the incident ray, the reflected ray and the normal line are in the same plane, the angle of incidence and the angle of reflection will always be equal.” So, illustrations of the light reflection must be in line with the incident ray, the normal line and the reflected ray in the same plane and the angle of incidence must be equal to the angle of reflection. Studies show that different objects reflect light differently and the reflection varies with the type of object surfaces. Flat surfaces can reflect more light than uneven surfaces and glossy, flat surfaces can reflect light better than uneven, matt surface. Law of reflection  The incident ray, the normal line and the reflected ray are always in the same plane.  The angle of incidence always equals the angle of reflection.

176 normal line i = angle of incidence r = angle of reflection incident ray reflected ray flat surface incident ray reflected ray convex surface incident ray reflected ray concave surface Picture 7: Reflection of light on different flat surfaces 2. Refraction of light Refraction happens when light travels through materials of different density and bends from its original line. The light may bend towards or away from the normal line, depending on the refractive indexes of the materials which it passes through. The law of refraction is as follows: - If light travels from a less dense material to a more dense material, the ray will bend toward the normal line. - If light travels from a more dense material to a less dense material, the ray will bend away from the normal line.

177 Light A Material with the Material with the refractive index of n2 refractive index of n2 Material with the Material with the refractive index of n1 refractive index of n1 Light A Light A’ Light A’ A. Bend outward B. Bend inward Picture 8: Different types of light refraction Commonly, the density of transparent materials is directly related to their refractive indexes. That is, materials with high density have high refractive index and materials with low density have low refractive index. Refractive index α Density Important facts about light refraction - Light frequency remains the same but the wavelength and the speed of light change. - Light does not change direction if it falls perpendicularly on the surface of the material. Otherwise, it will change direction. Example of the application of the light refraction principle is lamp covers which are made of glass or plastic and control the lamplight to move towards the target directions. The lamplight originally radiates in all directions but the lamp cover bends the light rays towards the same direction as seen in, for example, headlamps of cars and motorcycles. 3. Dispersion of light When white light which consists of different frequencies enters a prism, the light will refract twice (at the first boundary when it enters the prism and at the second boundary

178 when it exits the prism.) As a result, the beams separate into colors based on the wavelength and frequency which is called a spectrum. Angle of deviation White light Red Orange Yellow Green Blue Purple Background Picture 9: Light dispersion 4. Interference of light Interference occurs when 2 light beams combine in the same direction or in opposing directions. If light waves travelling in the same direction meet up, the light will become brighter. If light waves travelling in the opposing directions, the light will become weaker. Light interference principle is applied to cameras and projectors for light reduction and to reflectors for light amplification. 3.3 Natural phenomena involving light 1. Mirage - It is an optical illusion. On a hot day, we may see an illusion of a puddle on a road. Mirage happens because the air near the road surface is hotter than the air above it (cooler air has more density). So, the light gradually bends more and reaches the hotter air near the road surface at an angle which is larger than the critical angle, creating a total reflection. 2. Rainbow - It is a natural phenomenon which occurs because white light bends when it enters water droplets and disperses into a spectrum. Then, the light undergoes a total reflection on the back of the water droplets and refracts again when it exits the water droplets. Because of this, the white light disperses into different colors. Due to its dispersion property, the light disperses when it hits the surface of things. This principle is useful for reducing the brightness of light bulbs with a clear plastic material and lamp covers.

179 Picture 10: Rainbow phenomenon 3. Sun halo and moon halo - These phenomena occur when the white light of the sun falls on ice crystals in the atmosphere which line in an arc and undergoes refraction and total reflection in the crystals. Picture 11: Sun halo

180 Topic 3 Sound energy 4.1 Source and movement of sound Sound is a form of energy produced by object vibration. The volume of sounds is directly related to the vibration intensity. Sound is a mechanical wave and travels through a medium. It can travel through the air, solids and liquids but not through a vacuum. We hear sounds because sound waves move through the air which is the medium from their sources to our ears. Speed of sound - Speed of sound is relative to the medium property such as density and elasticity. Commonly, sound travels best in solids, followed by liquids and gas. Temperature of medium also determines the speed of sound and sound travels faster in higher temperature. Gas Liquid at 25ºC Solid Substance V (m/s) Substance V (m/s) Substance V (m/s) Air (0ºC) 331 Water 1,490 Aluminum 5,100 Air (100ºC) 336 Sea water 1,530 Copper 3,560 Hydrogen (0ºC) 1,290 Methyl alcohol 1,140 Iron 5,130 Oxygen (0ºC) 317 Lead 1,320 Helium (0ºC) 972 Rubber 54 Table 1: Speed of sound in different types of medium 4.2 Sound property Sound is a wave and has all the properties of a wave. 1. Reflection of sound It is a phenomenon occurring when a sound wave travels from a medium and reaches a barrier or a medium which is more or less dense than the first medium. In such case, it will reflect and travel back to the first medium. Sound will reflect better when its wavelength is less than the obstacle. Sound reflection works on the same law of wave reflection:

181 1. The incident wave, the normal line and the reflected wave are always in the same plane. 2. The angle of incidence always equals the angle of reflection. When sound travels from a medium to another medium which has more density, the phase of the reflected sound wave will not change. If sound wave travels from a denser medium to a less dense medium, one portion of the sound wave will reflect at a 180 degrees phase change while another portion will travel back to the medium. 2. Refraction of sound Sounds refract when they move between media of different temperatures. The media can be of the same type or different types. Change in sound speed will alter the direction of the sound wave unless the sound wave reaches the medium in a direction which is perpendicular to it. 3. Interference of sound Interference occurs when 2 or more waves meet. The result is that their amplitudes will combine and change the sound volume. In constructive interference, compressions of the waves match and the waves will combine to create larger amplitude which makes the sound louder. In destructive interference, the compression of one wave meets a rarefaction of another wave and their amplitudes subtract, making the sound quieter or sometimes inaudible. 4. Diffraction of sound Diffraction is a property of wave. As sound also behaves like a wave, it can bend around opaque barriers, corners or slits. Sounds will become quieter after they go through barriers because the sound energy is lessened. This phenomenon of sound diffraction can be explained by using Huygens' principle that \"any point on a wave front may be regarded as a source of a secondary wave.\"

182 4.3 Sound volume and hazardous sound Audible sounds have different traits and can be distinguished by their volume. What are the dangers of sound? Human ears can generally hear sounds with frequencies between 20 - 20,000 hertz. The frequency range which is very important for our daily life is the speech sound frequency which ranges from 500 ‟ 2,000 hertz. Ears have a limited level of ability to hear and tolerate sounds. If sounds are too weak, they are inaudible to human ears. Sounds that are too loud can be hazardous and cause an earache. Being in an environment which is too noisy such as textile factories, metal press factories, markets or busy roads can accelerate the impairment of hair cells and auditory nerves, causing impaired hearing and hearing loss. Prolonged exposure to a noisy environment can cause severe hearing loss, permanent hearing disability and thus the inability to communicate. Such disability would make life more difficult. How to be safe from the dangers of sound? Noise-induced hearing loss cannot be cured. To preserve the hearing, it is important to protect against noise exposure and this requires cooperation from all involved parties. Employers should ensure the good quality of building structures and materials as well as ensure that employees are provided with and use hearing protection devices such as earmuffs and plugs. Employees should also be given information about hazardous noises and encouraged to prevent themselves from hazardous noise exposure. Employers should arrange pre-employment and annual audiometric testing for employees to support evaluations and preventive planning. Employees should strictly follow employers' instructions and rules on hearing protection.

183 Lesson 12 Relationship between the Sun, the Earth and the Moon Main learning essence The relationship between the Sun, the Earth and the Moon is the cause of natural phenomena humans experience in their daily life such as the waxing and waning of the Moon, solar eclipses and lunar eclipses which result from the Moon’s revolution around the Earth or tidal waves which are affected by the gravitational force exerted on the Earth by the Moon and the Sun Traditions and stars, influence of astronomical phenomena on cultures, national traditions and myths such as Loy Kratong, Songkran, religious ceremony and folktales are all related to stars. Expected learning outcome Be able to explain the influence of the Sun and the Moon on celestial phenomena affecting the Earth and its application Content scope Topic 1 Natural phenomenon 1.1 Occurrence of day and night 1.2 Waxing and waning of the Moon 1.3 Solar eclipse and lunar eclipse 1.4 Season 1.5 Land breeze and sea breeze

184 Topic 1 Natural phenomenon 1.1 Occurrence of day and night The Earth is a natural satellite of the Sun. The Earth rotates around the Sun in an orbit. It takes the Earth 365 days or 1 year to complete the orbit and 24 hours to rotate once around itself. The part of the Earth which faces the Sun will be the daytime and the part that is facing away from the Sun will be the nighttime. The cycle is continuous as the Earth spins around itself and causes the occurrence of days and nights. North pole Night Sunlight Day South pole 1.2 Waxing and waning of the Moon The Moon is a natural satellite of the Earth and an opaque body. The diameter of the Moon is about 1/4 of the Earth's diameter. As the distance between the Moon and the Earth is only around 30 times the Earth's diameter, the Moon is the closest natural object to the Earth. The Moon can be seen from the Earth because the Moon surface reflects sunlight. The illuminated side of the Moon which faces the Earth shifts every day because the Moon travels around the Earth and completes its orbit around the Earth in around 1 month. This results in the apparent change in the size of the Moon such as a crescent Moon which grows larger and becomes a full Moon days afterward. This is called a waxing phase which means that the Moon is expanding in illumination. The waning phase is when the visible size

185 of the Moon is shrinking from the full Moon to a half Moon and then a small crescent before it reaches the \"new Moon\" phase or the phase when the Moon becomes all dark. The waxing and waning of the Moon is called the lunar phase. The calendar which is based on the lunar phase is called a lunar calendar. According to the Thai lunar calendar, there are 12 months in a year and the months are classified into odd-number months and even-number months. An odd-number month has 29 days, starting from the first day of the waxing Moon to the fourteenth day of the waning Moon. Odd-number months are the first month, the third month, the fifth month and the seventh month etc. An even-number month has 30 days and the fifteenth day of the waxing Moon is the middle of a month while the fifteenth day of the waning Moon is the last day of a month. Even-number months are the second month, the fourth month, the sixth month etc. The waxing and waning of the Moon refers to the visibility of the Moon's illumination as a result of its orbiting around the Earth. The illuminated side of the Moon shifts all the time, depending on the position of the Moon to the Earth. Umbra Total solar eclipse (A) Penumbra Penumbra Partial solar eclipse (B) Umbra View from space Annular solar eclipse (C) View from the Earth surface 1.3 Solar eclipse and lunar eclipse Solar eclipse occurs when the Sun, the Moon and the Earth form a straight line and the Moon is in the middle between the Sun and the Earth, causing the Moon's shadow to fall on the Earth. As a result, people on the Earth (who are in the zone covered by the Moon's umbra) will see a partial eclipse or a total eclipse of the Sun. Generally, the duration of solar eclipses is not very long. On 24 October 1995, a total solar eclipse could be seen from

186 Thailand and the phenomenon, from the first contact to the last contact of the eclipse, took 3 hours to complete. Solar eclipse occurs during daytime and on the fifteenth day of the waning Moon or the first day of the waxing Moon only. A total solar eclipse can be seen from the Earth surface covered by the umbra of the Moon's shadow as the sky will temporarily turn dark. A partial solar eclipse can be seen from the Earth surface covered by the penumbra of the Moon's shadow. If a solar eclipse occurs when the Moon is farther from the Earth so that the tip of the Moon's umbra cannot reach the Earth surface but the continuation of the umbra reaches the Earth surface, an annular solar eclipse will be seen from that region. Actually, the Moon is much smaller than the Sun. However, as the Moon is nearer to the Earth than the Sun, its apparent size is big enough to cover the Sun's disk. Solar eclipse There are 4 types of solar eclipses: - Partial solar eclipse: The Sun's disc is blocked only partially. - Total solar eclipse: The Moon totally blocks the Sun's disc. - Annular solar eclipse: The Sun's outer edge is visible as a ring. This type of eclipse occurs when the Moon is farther from the Earth and its apparent size is smaller than the Sun. - Hybrid eclipse: Due to the curvature of the Earth surface, a solar eclipse is seen as an annular eclipse from some regions of the Earth and as a total eclipse from other regions which is nearer to the Moon.

187 Observing solar eclipse Viewing the Sun with naked eyes, even during solar eclipses, can damage the eyes. Solar eclipses are very interesting and educational phenomena which should be studied. However, using tools such as binoculars or telescopes to observe the Sun or solar eclipses will hurt the eyes more severely. To observe the Sun directly, it is necessary to use specifically-designed tools which can filter out rays from reaching the eyes. Sunglasses cannot protect the eyes from dangers and infrared ray, an invisible radiation which is harmful to the retina. The safest way to observe the Sun is to project an image of the Sun through tools such as binoculars or telescopes onto a white sheet of paper and view the image on the paper instead. However, it is very important to make sure that nobody observes the Sun directly through the tools because such direct observation of the Sun can severely harm the eyes of the viewer. Extra care must be taken to prevent children from using the tools. The Sun can be directly observed only during a total solar eclipse which is a beautiful spectacle and not harmful to the eyes. During a total solar eclipse phenomenon, the solar corona and sometimes prominences which are normally invisible to can be seen. It is important to stop viewing the Sun slightly before the solar eclipse ends.

188 Solar eclipse occurrence Motion of the Earth and the Moon The Moon's orbit around the Earth is inclined at an angle of around 5 degrees to the plane of the Earth's orbit around the Sun (ecliptic). Because of this, at a new Moon, the Moon will usually pass above or below the Sun. A solar eclipse can occur only when the Moon crosses the intersection of these 2 planes. As the Moon's orbit is elliptical, its distance to the Earth varies by about 6% from its average value and the apparent size of the Moon can be larger or smaller than average. This effect leads to the occurrence of solar eclipses. Generally, the apparent size of the Moon observable from the Earth is slightly smaller than the Sun. As a result, annular solar eclipses are more common than other types of eclipses. On the other hand, total solar eclipses occur when the Moon is closer to the Earth than average. The Earth's orbit is elliptical as well and the distance between the Sun and the Earth varies constantly. However, this has minor effects on the occurrence of solar eclipses. The Moon completes its orbit around the Earth in approximately 27.3 days and this is called a \"sidereal month.\" However, as the Earth travels around the Sun in the same direction, an interval between one full Moon and another full Moon which is called a \"synodic month\" is 29.6 days and longer than the sidereal month. The passage of the Moon to the intersection between the Moon's orbit and the Earth's orbit (node) from south to north of the ecliptic is called a \"draconitic\" month which is slightly shorter than a sidereal month because the Moon's orbit is tilted by the Sun's gravity. It takes 18.5 years to complete a circuit of the nodes. A passage from a perigee or the point where the Moon is closest to the Earth to the next perigee is called an \"anormalistic month.\" An anormalistic month is not equal to a sidereal month because the Moon's orbit precesses. The perigees complete a circuit in approximately 9 years. Frequency of solar eclipse The Moon's orbit intersects with the ecliptic at 2 nodes that are 180 degrees apart. Therefore, there are 2 periods each year when the new Moon phase occurs close to these nodes, causing solar eclipses. Sometimes, in a given year, the new Moon occurs close

189 enough to an ecliptic during 2 consecutive months and thus there can be as many as 5 solar eclipses in that year. However, as the umbra of the Moon usually passes either above or below the Earth while the penumbra reaches the Earth surface, a partial eclipse occurs and is visible only from the Arctic region. Path of solar eclipse A total solar eclipse covers a short period of time because the Moon orbits rapidly around the Earth and, at the same time, the Earth travels around the Sun, causing the umbra on the Earth surface to move swiftly from west to east. A total solar eclipse which occurs when the Moon is very close to a perigee can be seen in a wide range of approximately 250 kilometers and lasts approximately 7 minutes. A partial solar eclipse caused by the Moon's penumbra can usually be seen in a much larger area. Benefit of solar eclipse observation During a total solar eclipse, astronomers can observe the Sun's corona which is generally unnoticeable because the photosphere of the Sun is much brighter. Solar eclipses have an exact frequency or cycle. It is possible to predict an occurrence of a solar eclipse based on the orbital speed around the Sun and the position of the Moon in its orbit around the Earth. More about solar eclipse Solar eclipse before sunrise and after sunset - Occurrence of solar eclipse before sunrise or after sunset is possible. Before it occurs, the sky will appear much darker than normal and the inferior planets (Mercury and Venus) will be visible near the sunrise or sunset point of the horizon when it is normally invisible because of the sunlight. Solar eclipse caused by artificial satellite - A solar eclipse does not occur when an artificial satellite is in front of the Sun because an artificial satellite or a space station is, unlike the Moon, too small to cover the sunlight. An artificial satellite must be approximately 3.35 kilometers in size to block the Sun and cause a solar eclipse. So, artificial satellites and space stations, like Mercury and Venus, can only transit the Sun. These transits occur swiftly and are difficult to notice. In addition, they do not cause darkness.

190 Lunar eclipse A lunar eclipse occurs when the Earth blocks the Moon from the sunlight on the night of the full Moon (the fifteenth day of the waxing Moon). The Earth is between the Sun and the Moon in a straight line and its shadow falls onto the Moon. A lunar eclipse is a phenomenon which occurs on the night of the full Moon (the fifteenth day of the waxing Moon) when the Moon, the Earth and the Sun are aligned on the same plane. As a result, the shadow of the Earth falls on the Moon and people in some regions which should have seen the full Moon on the fifteenth night of the waxing Moon see a lunar eclipse of different types instead. A \"total lunar eclipse\" occurs when the Moon moves into the Earth's umbra and the full Moon will slowly become darker. A total lunar eclipse takes approximately 1.5 hours. Afterwards, the full Moon will be totally brick-red because the sunlight is refracted by the Earth's atmosphere and the red wave which is the longest wave strikes the Moon. A \"partial lunar eclipse\" occurs when the Moon is partially under the Earth's umbra. Because of this, one part of the Moon becomes dark while another part turns brick-red. Sometimes, the Earth's shadow in an arc shape can be seen during lunar eclipses and this is a proof that the Earth is round. Lunar eclipses have small effects on the natural environment because they occur at night. However, there is a mythical belief that eclipses, both solar and lunar eclipses, are caused by a celestial monster eating the Sun or the Moon and that they bring disasters to the Earth. According to traditional Thai and Chinese beliefs, loud noises can ward off the eclipse's evil. So, Chinese people will light firecrackers or hit cooking pans and Thai people will clash coconut shells together or hit pestles against trees to drive the evil away. Lunar eclipse Earth Sun Moon

191 1.4 Changing of seasons Seasons A year is divided into seasons according to changes in weather. The reason for seasons is that the Earth's axis slightly tilts at around 23.44 degrees to its orbital plane. When the Earth revolves around the Sun, some parts of the Earth face the Sun and are in summer while the other parts get less sunlight and experience winter. From the illustration of seasons caused by the Earth’s revolution around the Sun, we can see that the northern hemisphere and the southern hemisphere have opposite seasons. Different regions on the Earth have different seasons. Temperate regions and polar regions have 4 seasons which are spring, summer, fall, and winter. Tropical regions which are regions near the equator have 3 seasons which are summer (dry hot season), rainy

192 season (wet season), and winter (dry cool season). Thailand is located in the tropical region and has 3 seasons. This is the image of the Earth’s position viewed from the north. On the far right is the position of the Earth when it is farthest to the Sun in December. It is called “December solstice.” This is the image of the Earth’s position viewed from the south. On the far left is the position of the Earth when it is farthest to the Sun in June. It is called “June solstice.”

193 Each year, the Earth reaches the points which are farthest to the Sun twice. The one in December falls on 22 December and is called “December solstice” while another which is in June falls on 21 June and is called “June solstice.” In temperate and polar regions, the intensity of sunlight varies with season, latitude, and the proximity to bodies of water. For example, the winter in the South Pole region which is in the Antarctic continent and quite far from the southern oceans is much colder than the winter in the North Pole region which is in the middle of the Arctic Ocean. This is because the climate of the North Pole region is influenced by the Arctic Ocean which prevents the region from being too cold or too hot. In temperate zone, the intensity of sunlight in different seasons has minimal variation. Image of the Earth in different seasons 1. Different regions on the Earth have different climate, temperature, atmospheric pressure, prevailing wind, humidity and rainfall, etc. 2. Climate difference among regions on the Earth is caused by the Earth’s axial tilt and rotation around itself and the Sun. Because of this, each region is exposed to the Sun at different time and has different seasons.

194 Variable of season Seasons of regions are affected by the following 4 variables:  Temperature  Atmospheric pressure  Direction of prevailing wind  Humidity Temperature 1. Regions having high temperature - Southern hemisphere: January is the summer in the southern hemisphere. Regions experiencing the temperature above 30 degree Celsius are deserts in Australia and the southern region of the African continent. - Northern hemisphere: July is the summer in the northern hemisphere. Regions having the temperature above 30 degree Celsius are deserts in the North American continent (Mexico), Asia (the Arabian Peninsula and India), and the northern region of the African continent etc. 2. Regions having low temperature - High latitude climate zone which extends from the Tropic of Cancer to the North Pole and from the Tropic of Capricorn to the South Pole. - Highland and plateau such as the Himalayan range, Andes mountain range and Tibet plateau etc. Atmospheric pressure Atmospheric pressure is the weight of the air exerted on the Earth surface. The weight of air in each region varies. Hot air which is lighter rises and cold air which is heavier flows in to take its place. This results in the circulation of air. - A tool used for measuring the atmospheric pressure is called a barometer. Types of atmospheric pressure ‟ Climate conditions of each region vary with type of atmospheric pressure as follows: 1. High pressure means the air mass which is heavy and layers of the air presses against each other above the Earth surface. Generally, cold air mass is heavy. When the

195 high pressure passes an area, such area will experience cold weather. The high pressure is represented by “H” on a weather map. 2. Low pressure means the air mass which is light and floats in the upper layers of the air above the Earth surface. These air layers do not have much pressure on each other. Generally, hot air mass is light and has low pressure. The low pressure is represented by “L” on a weather map. 3. Equatorial region gains more heat when the sunlight strikes perpendicular to the Earth surface. As a result, it experiences low pressure and air from the surrounding area which has high pressure (at the latitude of 30 degrees north and south) flows into the equatorial region. 4. The convergence of the north wind and the south wind at the equator results in rainfall in the area which is known as the Intertropical Convergence Zone or doldrums or low pressure trough or monsoon trough. Direction of prevailing winds 1. Movement - Prevailing winds are seasonal and move from high pressure regions to low pressure regions. Examples include the northeast monsoon which originates in high pressure areas in Mongolia, which is in the north of China, and brings cold and dry air to Thailand. 2. Characteristics - Prevailing winds originating from high pressure regions, especially Siberia in Russia which is known to have highest pressure, bring with them coldness and dryness to all parts of Asia. However, they will pick up humidity when they slide across the sea and this causes rain to the regions they pass such as the southern region of Thailand along the Gulf of Thailand where rain is common in December. Humidity 1. Humidity means the amount of vapor in the atmosphere which varies with geological factors. 2. Humidity in the air can take the form of cloud, fog, snow, hail and dew.

196 Seasons in Thailand Thailand is located in the region which is affected by monsoon. As a result, there are 2 seasons which are prominent in Thailand: the wet season and the dry season. The dry season can be sub-divided into summer and winter. In conclusion, there are 3 seasons in Thailand as follows: 1. Summer Summer in Thailand ranges approximately from mid-February to mid-May when the northeast monsoon sweeps out and the southwest monsoon comes in (the season is changing from winter to rainy season). During this period, the North Pole is facing the Sun and April is when Thailand is perpendicular to the Sun’s ray at noon and receives maximum sunlight. As a result, the weather is generally hot and sultry. However, during the hot and dry summer in Thailand, cold air mass may descend from China to the northern Thailand and clash with the hot air mass which is prevailing in the area, resulting in storms, heavy rains and strong gusts of wind or even hails which can cause damage. Storms occurring in summer are commonly known as “summer storms.” 2. Rainy season Rainy season lasts between approximately mid-May and mid-October. It begins when the southwest monsoon which carries humidity and the low pressure trough (which causes rain) comes into Thailand. Because of this, rains are prevalent throughout Thailand. Generally, the low pressure trough passes the south of Thailand in April and ascends to the central region, the eastern region, the northern region and the northeastern region in May and June respectively. In late-June, the low pressure trough will flow up to southern China, resulting in a temporary period of less rain in Thailand which is called a “rain deficit period” and lasts for 1-2 weeks or, in severe cases, even a month or longer. Between August and November, the low pressure trough will move southward to Thailand, flowing from the north to the south and bringing heavy rainfalls which will be prevalent in the upper part of Thailand from August to September and in the lower part of Thailand from October to November. Throughout these periods, Thailand’s weather is also under the influence of the southwest monsoon and the severity of its influence depends on the position of the low pressure trough.

197 Around mid-October, the northeast monsoon or cold wind will begin to slide across Thailand and take the place of the southwest monsoon. This marks the beginning of winter in the upper part of Thailand. However, the south of Thailand, especially on the east coast, will continue to experience heavy rainfalls until December because the northeast monsoon descending from China across the South China Sea and the Gulf of Thailand will bring humidity to the region 3. Winter Winter begins around mid-October and continues until mid-February. The northeast monsoon which brings cold air with it passes Thailand in mid-October when the South Pole is facing the Sun. During winter, the Sun’s ray strikes the Earth’s surface in the Antarctic region at the right angle at noon while Thailand receives sunlight in non-perpendicular lines. Location of the low pressure trough, monsoon direction, and passages of tropical cyclones transiting Thailand are shown in the picture below. Illustration of low pressure trough, monsoon direction and passage of tropical cyclone Note: Low pressure trough may be weak and not obvious or deviate from the above plotting. 1.5 Occurrence of land breeze and sea breeze Occurrence of breeze When the air is heated, it expands, becomes less dense and rises. This causes “air current”. When hot air rises, cooler air will flow in a horizontal direction to replace it. The air which flows in a direction parallel to the Earth surface is called “wind”. Wind commonly

198 flows from an area with lower temperature or higher pressure to an area with higher temperature or lower pressure. During the day, the air temperature above the ground is higher than the temperature of air above water, though they both receive equal amount of heat from the Sun, due to their difference in heat capacity. At night, the land temperature is lower than the water temperature because it can release heat radiation faster than water. This principle is related to the occurrence of land breeze and sea breeze. - During the daytime, the air above the land surface is hot and rises. Then, the air above the water surface which is cooler blows in to replace it. This type of wind which flows from the sea to the land is called sea breeze. - At night, the warmer air above the water will rise and be replaced by the cooler air from the land. This type of wind which flows from the land to the sea is called land breeze. Knowledge about land breeze and sea breeze is useful for fishermen as the breezes help them sail out to the sea at night and return to shore in the morning.

199 Monsoon Monsoon is a seasonal wind and blows through specific regions. It covers a large area and is found only at a specific time of each year. Due to the Earth’s axial tilt, different regions on the Earth receives different amount of solar radiation. This results in the shift of temperature and air pressure which causes seasonal winds. There are 2 different types of monsoons: 1. Summer monsoon is a wind that blows from the sea to the land and forms in summer. Summer monsoon carries humidity or rain from the sea to the land. In Asia, this type of monsoon is also known as southwest monsoon and prevails in the region for 6 months, from April to September. 2. Winter monsoon flows from the middle of the continent which has high pressure to the ocean which has lower pressure and brings cool and dry air with it. This type of monsoon is also known as northeast monsoon and prevails in the region for 6 months from October to March. Wind direction You can tell the wind direction by observing natural surroundings such as the fumes of smoke, billowing tree leaves or waving flags. However, the wind direction suggested by these objects may not be exact. There is an invention called “wind vane” which can measure the direction of the natural winds. Wind vane Wind vanes should be placed at high spots such as the roof top. The arrow points toward the direction which the wind is flowing from. If the arrow is pointing towards the north and the west, it means that the wind is blowing from the northwest. If the arrow is pointing towards the south and the east, the wind is coming from the southeast.

200 Sometimes, the wind direction is measured in degree. The north (N) is at 0 degree (or 360 degrees) while other directions are measured clockwise from the north. The east (E) is at 90 degrees, the south (S) is at 180 degrees, and the west (W) is at 270 degrees. Northwest North Northeast West East Southwest Southeast South Nowadays, wind directions are reported in degrees for the purpose of weather mapping. For example, the wind coming from the east is called the east wind or the wind direction of 90 degrees while the wind coming from the southwest is called southwest wind or the wind direction of 225 degrees. Wind speed Winds blow at different speed. Winds blowing at higher speed can cause more serious damage. Natural winds can cause damage if their speed reaches 62 kilometers per hour or higher. At the speed of 89 kilometers per hour or higher, the wind can damage houses and buildings. Storms achieving the wind speed of higher than 118 kilometers per hour can cause widespread and serious damage. Thunderstorm A thunderstorm occurring in summer is generally called a summer storm. It is caused by a disturbed state of air which occurs rapidly and drastically and results in heavy rain, lightning, thunder, thunderbolt and sometimes hail. A thunderstorm which occurs in the