As the substances are heated up they get bigger and expand in sizes. The liquid, gases and solid expansions occur when it is heated up. Things shrink when they get cold. If the things expand with the addition of the heat it makes sense that they contract when the heat is removed. If you remove enough heat from the gas it will become a liquid.
Examples of expansion and contraction:
- Railway tracks consist of two parallel metal rails joined together. Small gaps, called expansion gaps, are deliberate. Left between the rails as there is an expansion of the rails in hot weather.
- If we hold a very hot glass tumbler under cold water. it cracks. This is because the outer surface of the glass comes in direct contact with cold water and contracts more as compared to the inner surface.
- Water expands on heating try this with the help of an adult. Take a glass filled with water to its brim. Pour the water into a container and heat it does not boil. Now try to pour the water back into the same glass. The water overflows.
- We observed that water expanded on heating. Can you say what will happen if the water is allowed to cool down and the glass? It would not overflow this is because of concentration.
Expansion and contraction in daily life:
- Engines of motor vehicles run when gases expand.
- When telephone wires are made, they are not pulled
together tightly because on cold days they can contract and snap.
- When making steel rims for wheels.
- Space is left between rails on a railway line so that the rails
will not bend on a hot day.
- When the screw-cap of a bottle cannot be opened.
- Oil and steam pipes are made with loops at certain places
to provide for expansion and contraction of the pipes.