The Factors are Temperature and kinetic energy, the temperature is because the particles are going to move fast which means the particles in a solid container or in solid pattern they will actually vibrate and they will expand , when temperature increase, more kinetic energy between the particles .
examples is that in the steel when you heat a steel the particles inside it will vibrate then the particles speed up because the vibration increases, therefore the temperature increases so a a thermal expansion occurs that the vibration of the particles will take up more space so the steel bar expands slightly in all Direction if the temperature Falls the reverse happens and the material or steel contracts which means get smaller .
another example is the thermometer, the thermometer has a liquid inside it which is Mercury or alcohol this liquid expands when the temperature rises, the tube is made narrow so that a small increase in volume of the liquid produces a large movement along the tube.
examples is that in the steel when you heat a steel the particles inside it will vibrate then the particles speed up because the vibration increases, therefore the temperature increases so a a thermal expansion occurs that the vibration of the particles will take up more space so the steel bar expands slightly in all Direction if the temperature Falls the reverse happens and the material or steel contracts which means get smaller .
another example is the thermometer, the thermometer has a liquid inside it which is Mercury or alcohol this liquid expands when the temperature rises, the tube is made narrow so that a small increase in volume of the liquid produces a large movement along the tube.