physics notes

Bicycle Pump

When the piston is pushed into the cylinder, the air in the cylinder is compressed.

According to Boyle's Law, the air pressure inside the cylinder will increase.

This causes the air pressure in the cylinder to become higher than the pressure inside the tyre. Therefore, the air can flow into the tyre.

2. Hot-air baloon

When the air in a balloon is heated at atmospheric pressure, its temperature will increase.

According to Charles' Law, the volume of gas in the balloon will increase when its temperature increases.

Thus, the upward thrust on the balloon will increase when the volume of air displaced by the balloon increases.

Therefore, the balloon will climb upwards if the upward thrust exceeds the weight of the balloon.

3. Car Tyre

When a car is moving, the car tyre will experience frictional force and compression. This condition causes the temperature of the air inside the tyre to increase.

According to the Pressure Law, the rise in tyre temperature will cause the pressure inside the tyre to increase until an optimum level. Therefore, it is wise to pump the tyre just slightly below the recommended level. Anyway, we must also adjust the pressure of the tyre according to the temperature when we pump the tyre.