EXPANSION AND CONTRACTION OF GASES
• Gases that are heated expand in their containers.
• The energy of the gas particles increase by heating.
• The particles of warm gases hit the walls of the container and they hit it harder.
• If the walls of the container are flexible, the walls expand.
• If the walls are not flexible and cannot expand, then the pressure inside the container increases.
• A few examples of gases that expand and contract are:
(i) Air in balloons
(ii) Air in tyres
(iii) Air in an air mattress
(iv) Air in a football, volleyball, etc
• The helium gas in a balloon expands when we move a balloon from the cold outdoors to a warm room.
• At a low temperature, the average kinetic energy of the particles in the balloon is low.
• The particles do not collide as often with the walls of the balloon, and hit the walls with less force. So, the balloon contracts.
• As the temperature of the gas inside the balloon rises, the particles move faster and hit the wall of the balloon more often. So, the balloon expands.
Cars and bicycles:
• When cars and bicycles travel, their tyres rub on the road.
• This makes the tyres get hot. The air inside the tyres will expand.
• If the tyres are too full, they could burst.
• Sports balls such as footballs are also filled with air.
• If we leave a football out in the cold, the air inside the ball will contract. The ball will get soft and it will become unusable.