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www.GOALias.blogspot.com4HeatIn Chapter 3 you learnt that woollenclothes are made from animal fibres.You also know that cotton clothesare made from plant fibres. We wearwoollen clothes during winters when itis cold outside. Woollen clothes keep uswarm. We prefer to wear light colouredcotton clothes when it is hot. These giveus a feeling of coolness. You might havewondered why particular types ofclothes are suitable for a particularseason.In winter you feel cold inside thehouse. If you come out in the sun, youfeel warm. In summer, you feel hot eveninside the house. How do we knowwhether an object is hot or cold? Howdo we find out how hot or cold an objectis? In this chapter we shall try to seekanswers to some of these question.4.1 HOTAND COLDIn our day-to-day life, we come across anumber of objects. Some of them are hotTable 4.1: Hot and cold objectsObjectIce creamCold/Coolool√Warm/Hototand some of them are cold. Tea is hotand ice is cold. List some objects youuse commonly in Table 4.1. Mark theseobjects as hot or cold.Do not touch objects which are toohot. Be careful while handling acandle flame or a stove.We see that some objects are coldwhile some are hot. You also know thatsome objects are hotter than otherswhile some are colder than others. Howdo we decide which object is hotter thanthe other? We often do it by touchingthe objects. But is our sense of touchreliable? Let us find out.Activity 4.1Take three large mugs. Label them asA, B and C. Put cold water in mug Aand hot water in mug B. Mix some coldMake sure that water is not so hot thatyou burn your hand(A) (B) (C)Spoon in atea cupFruit juiceHandle of afrying pan Fig. 4.1 Feeling water in three mugs