Page 128 - Active Science 5 Ebook and Activity

This process is called melting. Upon heating, some solid molecules move apart which
cause the wax to expand.

Upon heating a gas, the molecules expand because they move very fast.

Activity 11.3

Aim : To show that air expands upon heating.

Materials Required : A hard plastic bottle with a lid, modelling clay, transparent drinking
straw, a pair of scissors, tap water

Procedure : • Take the bottle. Cut its lid to make a hole with
the help of a pair of scissors.
• Put a drinking straw in the bottle through the
Clay
hole.
• Fill the bottle halfway with cold water. Food Colour

• Add a few drops of food colouring and mix.
Straw
• Make sure that the straw does not touch the
base of the bottle. Water

• Seal the hole in the lid using clay, so that the
straw gets fixed in place. The seal must be Bottle expands

completely airtight.
• Place one hand on the upper part of the bottle.

Observation : The heat from your hand will heat the air inside the bottle. The air
expands and allows the water to rise in the straw.

Cooling of Solids, Liquids and Gases

When a solid cools down, the molecules move slowly and come closer to each other. This

is called contraction.

When we cool a liquid, the movement of molecules slow down. On further cooling, the
molecules come closer and rearrange to transform into a solid. This is called freezing,
i.e., when liquid changes into a solid.

When a gas cools down, the molecules come closer and rearrange to transform into a
liquid. This is called condensation. Some common examples of condensation are dew

drops on a leaf, water droplets on a glass of cold water.

C hanges in States of Matter

There are two changes in the states of matter:

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