What shows the direction of energy transfer?

Energy can be in a multitude of forms and transferred in many ways, but for the purpose of this answer, I will focus on a main way that energy is transferred-- as heat.

The direction of energy transfer is always from objects that are hotter to objects that are colder.

There are three types of energy transfer:

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  Radiation: Radiation is the transmission of energy through empty space. Example: Energy from the sun is transferred by radiation.

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  Conduction: Conduction occurs when energy is transferred by collisions between particles. Materials that are good at transferring energy by conduction are called conductors. Example: Energy is transferred in copper metal through contact between individual copper atoms.

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  Convection: In convection, heat is transferred by the movement of mass within a fluid. The fluid can be a gas or a liquid. Example: In the atmosphere, warm air rises and cold air sinks.

When energy is transferred to an object, it becomes warmer. In order for an object to cool, energy must be removed.