Temperature and Particles
When you add heat energy to a substance, for example heating up the air in a hot air balloon, then you are adding more thermal energy to the particles of the substance.
This makes the particles of the gas, liquid or solid move faster.
So in a gas, if you add thermal (heat) energy, then you will make those particles move faster in straight lines so that they collide with each other and the walls of the container with more force.
If you add more thermal energy to a liquid, then the particles will move faster around each other (remember that liquid particles are close together but can slide around each other).
If you add more thermal energy to a solid, where the particles are held in position by strong solid bonds, then you make the vibrations of the particles about their fixed positions much larger.
As we add more thermal energy, the temperature of the material will increase. Temperature is simply a measure of the thermal energy of a substance.
The higher a substance's temperature, then the faster its particles move if it is a liquid or gas, or vibrate if it is a solid.
This means that hotter particles have more internal energy. Internal energy is the sum of the thermal energy of the particles (i.e. their total kinetic energy) and the potential energy of the particles due to the bonds between the particles.
In a solid, the bonds are strong, so the bond energy makes up a significant part of the internal energy of the solid*
In a gas, the bonds between particles are almost non-existant, so the internal energy of a gas is equal to the thermal (kinetic) energy of the particles.
*N.B. Physicists actually define the potential energy of gas particles to be zero. This 'reference' point means that the potential energy of solid particles becomes negative because energy must be put in to break the bonds.
GCSE Physics Keywords: Temperature, Particles, Vibration, Internal Energy