Work and energy - Higher

Pressure can be increased by:

  • increasing the temperature - this increases the freqency and force of collisions
  • decreasing the volume - this increases the frequency of collisions but not the force

A force applied to the particles in a gas causes a transfer of energy.

A piston closes the end of a cylinder with some gas molecules inside. The pressure applied to the piston is doubled and the volume inside the cylinder halfs.

When a person presses a piston down on a column of gas, they apply a force to move the piston a certain distance.

Work is done on the gas to compress it:

work done (J) = force (N) × distance (m)

curriculum-key-fact
Mechanical work transfers energy from the person or machine's store of chemical energy to the thermal energy store of the gas.

The volume of the gas decreases so the pressure increases. This is because the gas particles are moving in less space, so they collide with the container walls more often.

The temperature of the gas is not fixed in most applications, and the increased pressure leads to an increase in temperature. Temperature is a measure of the average kinetic energy of particles, so an increase in the energy store of the gas (as kinetic energy of the particles) means that the temperature must increase.

This process explains why a bicycle pump gets warm when it is used to inflate a tyre.