Matter is made of tiny particles (atoms and molecules)
These particles are always in motion.
The kinetic energy of the particles remains constant if the temperature
and pressure of the substance remains constant.
Kinetic energy = 1/2mv2 (m=mass and v=velocity)
Temperature is a measure of the average kinetic energy of the atoms of a substance. Higher
average kinetic energy = faster moving molecules or atoms = higher temperature.
Pressure is related to the impacts of molecules. Higher avearge molecular kinetic energy
= Increased number of impacts and increased speed of impacts = higher
pressure.
See the Flash plugin below to see demonstration of Kinetic Molecular
Theory: