Heat is the energy transferred from one object to another attributed to a property of substance called temperature.
Heat energy actually causes the movement of tiny particles of the material to raise its temperature or change the phase of the material.
The SI unit of heat is Joules (j).
Heat is unidirectional and always flows from a body of higher temperature to a body of lower temperature.
Objects cool down by releasing energy to their surroundings in the form of heat. The object then raises its temperature by gaining energy in the form of heat from its surroundings. The higher the temperature of an object, the more likely it is to transfer heat.
A substance can absorb heat without raising the temperature by changing from one state of substance to another, from solid to liquid (melting), from solid to vapor (sublimation), and from liquid to vapor (boiling).
The process of heat transfer occurs mainly in three different ways:
Conduction: It is the process of heat transfer in the matter by communication of the kinetic energy of 1 particle to the next without the actual movement of particles of the medium.
Convection: It is the process of heat transfer through bulk particle motion in a medium.
Radiation: It is energy transfer through EM waves without the presence of a medium in between.