咩係internal energy?!

internal energy is the sum of kinetic energy and potential energy, ie the total energy stored in the object.

internal energy can be increased by 2 ways:
heating and doing work.

geneally, increase in KE implies an incease in the speed of the object, ie drop in KE implies drop in speed.
increase in PE implies rise in height and vice versa.
KE can be calculated by 0.5mv*2 and PE can be calculated by mgh.
also,even internal energy rises, KE does not have to rise provided that the increase in PE can compensate the drop in KE and also vice versa. So, if all these changes happen at constant temperature, they are all work done to increase internal energy of a body.

for heating, it will affect internal energy of a body microscopically. an object is made up of many molecules. the molecules move randomly inside the object. temperature increase can increase the speed of the randomly moved molecules and thus increase KE. change in state of the object like from solid to liquid to gas, PE is increased.

Internal energy is the total energy stored in a body. Whenever a body absorbs heat, its internal energy increases.
Since internal energy is the sum of energy of all the molecules in a body, it depends on:
1. the amount of molecules in the body (size of the body)
2. the temperature of the body (kinetic energy)
3. the material from which it is made (potential energy)