HOW HEAT BLOWS UP A BALLOON
Stretch a rubber balloon over the neck of an “empty” bottle. Put the bottle into hot water, or light a candle and hold the bottle over the flame.
You will see that: The balloon blows up.
When heat is added, the molecules of air in the bottle move faster and farther apart and therefore the gas (air) occupies more space. As more and more air flows into the balloon from the bottle, the walls of the elastic balloon are pushed out by the air.
Heat has caused the air to expand. What do you think will happen when you remove the heat? Try it. Now you know why it is necessary to check balloon tires during hot weather.