SCERT Kerala State Syllabus 8th Standard Basic Science Textbooks English Medium Part 1

On the basis of the given information, answer the Precautions to be taken following questions: while measuring length z The use of plastic carry bags having thickness While measuring the length of an below the stipulated level has been object, keep the scale close to the prohibited. In which unit is the thickness of object without any inclination, as such bags expressed? shown in Figure 8.9(b) z The distance from the earth to a planet in the u solar system is 4 AU. What do you mean by this? z Find out how many kilometre is one light year and write it down in your science diary. z Which is the convenient unit to express the Fig 8.9 (a) distance from the earth to the star thiruvathira? In order to measure the length of an object 9 accurately, we should be careful about certain points. Try to understand these points analysing Fig 8.9 (a) (b) (c). What will you do if the edges of a scale are broken Fig 8.9 (b) or if the markings are not clear? Note it down in The position of the eye is very important your science diary. while taking the measurement. Observe z Instead of measuring from the first marking the figure 8.9(c) and understand where on the scale start from another whole number. the position of the eye should be. $ Fig 8.10 Fig 8.9 (c) z What is the length of the pencil shown in Fig 8.9 (c)? Note it down. Now you might have understood the basic unit for measuring length and its smaller as well as bigger units. You might have also observed the situations in which length is to be measured. Have you ever bought sugar from a shop? In which unit do you get it? What does this measurement indicate? Fig 8.11 Basic Science VIII 107

Fig 8.12 (a) Fig 8.12 (b) Mass Fig 8.13 Observe the picture showing how sugar is weighed in a shop. l It is done after placing a weight block in one pan. What is the purpose of placing the weight? l How are the measurements in both the pans in the second picture? This is done to get the same amount of sugar as that of the matter in the weighing block. Mass of a substance is the measure of the quantity of matter contained in it. Observe the weight block shown in Fig.8.13 What is the marking on it? On each weight block its mass will be marked. The mass of the weight block shown in the figure is 2 kilogram. The basic unit of mass is kilogram. One kilogram mass The basic unit of mass is kilogram. Its symbol is kg. We consider one kilogram as In addition to the basic unit kilogram, we use other the mass of a cylinder made of smaller as well as bigger units to suit our convenience an alloy of 90% platinum and for measuring mass. milligram (mg), gram (g), quintal, 10% Iridium kept at the tonne etc., are some among them. From the table given International Bureau of below find out their relationship with kilogram. Weights and Measures in Paris. Measurements Value in kilogram(kg) A similar one is kept at the 1 mg 1/1000000 kg = 1 kg =10-6 kg National Physical 106 Laboratory in 1g New Delhi. 1 quintal 1/1000 kg = 1 kg =10-3 kg 1 tonne 103 100 kg = 102 kg 1000 kg = 10 3 kg Table 8.2 108 Basic Science VIII