For example, rain. Do we pull the raindrops towards the ground? No, they are pulled towards the ground by some other force. In the same way, the ball that we throw up comes back without anyone pulling it. The force that pulls objects towards the Earth is called gravity. FRICTION raindrops ball thrown up We have learnt that force is needed to stop a moving object. comes down Now, roll a ball slowly. After some time, the ball stops rolling on its own. Think, when your bicycle’s tyre goes flat, is it easy to pull the cycle to reach home? Why is it so tough? It is because of friction. Friction is a force that stops the movement of two things flat tyre of the bicycle touching each other. Friction can be thought to be caused by bumps on two things. On smooth surfaces, things move longer distances. On rough surfaces, the movement stops soon. This is because things with a rough surface cause more friction. When we hold anything with our hands, there is friction acting between our fingers and the object. Due to the friction, the object does not slip out of our hand. Friction helps us hold things tight. Have you noticed that oil on our hands makes it more slippery? Oil forms a layer over the surface and reduces its roughness. So, the friction becomes low. Train My Brain 1) Which force pulls objects towards the Earth? 2) Name a force that acts to stop a movement. I Apply When we apply force on an object to move it, stop it from moving or change its shape, we do work. Force and Work 47
For example, we pick up a box from the ground. lifting a box hitting a ball The box moves from its original position. The force with a bat we put on the box made it move. So, we did work. When we hit a ball using a bat, the force we apply makes the ball move to another position. So, we can say that some work is done. Be Amazed Have you observed that tyres of vehicles have tyre with a rough surface grooves and spikes in them? This is to make the surface rough and increase friction. Tyres with good friction prevent skidding when you apply the brakes. I Explore (H.O.T.S.) In our daily life, we do many activities and say that we have done some work. But in science, work is not done in every activity. Here are a few pictures. Identify the objects that are moving and those that are not moving. Tick mark the pictures where some work is done. Work is done when things move from their place. falling leaf moving car girl sitting with books on her head Measuring work can sometimes be tricky. For the work to be done, the position of the object should change from one point to other. 48
If you push the wall with all your energy but the wall doesn’t move, no work has occurred. This is because the wall did not change its position. Sometimes, we may apply a lot of force to move something. But if things don’t move on putting force, then it means that no work is done. pushing the wall Connect the Dots English Fun Super An acrostic poem is a kind of poem in which the first, last or Cool any other letter of each line together forms a word. Look at the Happy example of acrostic poem for the word ‘school’. On time Outdoor play Write an acrostic poem, where the first letters of the lines form the Learning word WORK. W________________________________________________________ O________________________________________________________ R_________________________________________________________ K_________________________________________________________ Maths Fun During the sports day at school, Riya participated in a 200 metre race. The track for the race was a circle. What is the work done? racing track A Note to Parent Try out the different activities given in the lesson with your child at home. Help them understand the concept of force and work using these activities. Force and Work 49
Lesson Forms of Energy 17 I Will Learn About R energy and its sources. u forms of energy. a uses of energy. h saving energy. I Think We need energy to do any work. We get energy from the food we eat. Have you ever wondered what energy is? Where does this energy come from? I Remember boy kicking football with force Do your parents tell you to drink milk or eat vegetables to get energy? We hear the word energy often. What do you do to kick a football? We have learnt in the last lesson that we need force to move, stop or change the shape of an object. We put force on the ball to move it. To put force, we need energy. So, all types of forces have some energy linked with them. 50
Where does the food we eat get the energy from? The Sun is the basic source of energy plants using solar energy kid eating food for energy on the Earth. The energy we get from the Sun is called solar energy. We can feel the solar energy in the form of light and heat. Plants use this energy to make their food and store it in different plant parts. Some energy is used for the growth of the plant. When we eat plant parts, we get the energy stored in plants. Other than Sun, there are some other energy sources. Let us recall what they are: • Where do vehicles get the energy to run? They get the energy from fuels. • The wind is another source of energy. • Moving water is also an important source of energy. fuel as energy source trees swaying due to the wind flowing water as an energy source Some sources of energy like the Sun, wind and water are not The Sun, wind, water limited, while other sources like fuels are limited. They may get and fuels are natural over someday. We must save all kinds of energy sources. sources of energy for us. Think, can we hold energy in our hands? Try to hold wind energy or running water from the tap. We cannot hold energy. Energy has no shape. Forms of Energy 51
I Understand We have learnt that we get energy from different sources. Now, let us learn about different forms of energy using some examples. 1) Do you find any difference between day and night theatre with few lights when there are no bulbs or tube lights? It is the presence of light. When you go to the theatre to watch a movie, is it easy for you to find your seats? It is dark until the movie starts. Light is the form of energy we can see. 2) Rub the palms of your hands 10–15 times. Now, quickly touch your eyes with your palms. What do you feel? We can feel the warmth. This form of energy is heat. 3) Try blowing on a notebook from the side. What rubbing the palms place palms on eyes happens to the pages of the notebook? Think, about what you do when you want to blow a balloon. The wind energy from your mouth made the pages move and the balloon expand. 4) Look at the electric bulbs and fans in your wind used to blow a balloon classroom. Where do they get the energy to work? They use electricity or electrical energy. 5) Throw your eraser slowly towards the roof. Did it stop near the roof or the floor? Gravity pulls everything down. Train My Brain 1) What do plants use solar energy for? 2) Which form of energy can we see? 52
I Apply We need energy to do work, whether sitting, standing, running or sleeping. We need energy: • for our body to do different work. • to light up bulbs, tube lights and so on. • to use phones, televisions, computers and so on. • to cook food. • to cool or heat homes and offices using fans, heaters and coolers. • to run vehicles. Be Amazed Have you seen lightning during the rainy lightning season? It is the natural form of electricity. It is very powerful. It can burn everything on its way. During lightning, we should avoid standing under a tree. I Explore (H.O.T.S.) It is important to save or conserve energy. Some of the easy ways to save energy are: 1) Turn off fans, lights and other electrical devices when not in use. 2) Lots of energy is used in making paper and plastic. So, we should recycle these things to make newspapers, bottles and so on. We should not waste paper from our notebooks. We should also try to use less plastic. We should use jute and paper bags instead of plastic bags. 3) We should use renewable energy more than non-renewable energy. Forms of Energy 53
Connect the Dots English Fun Adjectives are describing words. Make adjectives using the following nouns: 1) heat: _________________________________________________________________________ 2) Sun: _________________________________________________________________________ Social Studies Fun Archimedes, a Greek mathematician, used solar energy to defeat his enemies. He used ‘heat rays’ to burn the enemies' ships. Find out how. (Hint: using a mirror to focus the sun’s rays onto the ships) A Note to Parent Help your child to identify different sources and forms of energy used at home. For example, a solar cooker uses solar energy, a television and the computer use electric energy and so on. 54
Inside the Lab – C Make sure you do these activities only with the help of a teacher or an adult. Activity C1: Building a Shelter You will need: chart papers, cardboard boxes, coloured/crepe papers, crayons or colour pencils, glue or tape, craft paper You need to: 1) Make groups of students, and provide them with cardboard boxes. 2) They need to build a model shelter using the materials provided. 3) For making a shelter using cardboard boxes, the following steps can be helpful: Step 1: Take a cardboard box. Step 2: Draw the outlines for doors and windows on it. Step 3: Cut the doors and windows, and stick craft paper as you need. (Teacher should help the students while cutting.) Step 4: Make a roof for your cardboard house by cutting small pieces of cardboard as shown in Step 4. Step 5: You can make different types of houses as shown in Step 5. step 1 step 2 step 3 step 4 step 5 55
4) For building a shelter using chart papers, you can use the following steps: Step 1: Draw the outline of the house on the chart paper. Cut the paper along the borders. (Teacher should help the students while cutting.) Step 2: Fold the paper on the outlines. Step 3: Cut the windows. Step 4: Stick the border as shown in Step 4. Step 5: Paint it or use craft papers to decorate this shelter. You can even put lights in it. step 1 step 2 step 3 step 4 step 5 Activity C2: Power of Solar Energy Let us use sunlight and a magnifying glass to make a fire. You will need: paper, small pieces of dry wood, a magnifying glass, a bucket of water to put out the fire You need to: 1) take a piece of paper to an open ground where you get bright sunlight. (Carefully select a place where the fire cannot spread and burn anything else) 2) take a small piece of dry wood, and place the paper over it. 3) hold the magnifying glass in such a way that the sunlight falls on it and all the light is focused on the paper. A small, bright dot will appear on the paper. 4) wait for some time. After a while, you can see that the paper catches fire. 5) put off the fire as soon as it ignites by pouring water on it. (Take help from the teacher.) 56
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