NCERT Book Class 7 Science Chapter 3 Heat

3 Heat

Y
ou know that woollen clothes are and some of them are cold. Tea is hot
made from animal fibres. You and ice is cold. List some objects you
also know that cotton clothes are use commonly in Table 3.1. Mark these
made from plant fibres. We wear woollen objects as hot or cold.
clothes during winters when it is cold
Do not touch objects which are too
outside. Woollen clothes keep us warm.
hot. Be careful while handling a
We prefer to wear light coloured cotton
candle flame or a stove.
clothes when it is hot. These give us a
feeling of coolness. You might have We see that some objects are cold
wondered why particular types of while some are hot. You also know that
clothes are suitable for a particular some objects are hotter than others
season. while some are colder than others. How
In winter you feel cold inside the do we decide which object is hotter than
house. If you come out in the sun, you the other? We often do it by touching
feel warm. In summer, you feel hot even the objects. But is our sense of touch
inside the house. How do we know reliable? Let us find out.
whether an object is hot or cold? How
do we find out how hot or cold an object Activity 3.1
is? In this chapter we shall try to seek Take three small tubs/containers. Label
answers to some of these questions. them as A, B and C. Put cold water in
3.1 HOT AND COLD container A and hot water in container
In our day-to-day life, we come across a Make sure that water is not so hot that
number of objects. Some of them are hot you burn your hand
Table 3.1: Hot and cold objects
(A) (B) (C)
Object Cold/Cool Warm/Hot
Ice cream 
Spoon in a
tea cup
Fruit juice
Handle of a
frying pan Fig. 3.1 Feeling water in three containers