When you heat a substance, you are transferring energy into it by placing it in contact with surroundings that have a higher temperature

Example:

When you place a pan of cold water on a stove burner - the burner is at a higher temperature than the water, and so the water gains energy. 

What is HEAT?

Heat is defined as form of energy which’s transferred across the boundary of a system due to a temperature difference between the system and its surroundings.

Heat can change the state of substances 

When

heated

Unit of  HEAT

Heat is measured in Joule (J) or calorie (cal).

1 Joule  = 0.24 calorie   1 calorie = 4.2 Joule. 

If an object has become hotter,
it means that it has gained heat energy.

If an object cools down, it means it has
lost energy