Matter will transfer thermal energy in one of three ways: through conduction, convection, and radiation. When two objects of differing temperatures are put together, the objects will endeavor to reach thermal equilibrium. That is, heat will be transferred from the higher concentration to the lower concentration—from hot to cold. In other words, the hotter object will transfer heat to the cooler object until both objects have the same temperature. Once the objects reach equilibrium, they will tend to stay there unless there is some sort of external change.
The molecules in an object with higher thermal energy vibrate faster than an object with low thermal energy. The moving molecules can then bump into other molecules, causing them to move as energy is transferred. Conduction is what happens when objects transfer thermal energy by molecules bumping against each other. This can be seen when a metal spoon is dipped in hot tea. The molecules from the tea vibrate against the molecules in the spoon, causing the molecules to speed up and thus causing the spoon to heat up.
Another way to move thermal energy is convection. Convection has to do with heat being transferred through the movement of fluids. There are two types of convection: natural and forced convection. Forced convection uses objects like a pump or a fan to move fluids and transfer heat. Examples of forced convection include convection ovens and fluid heat radiator systems.
Natural convection occurs when a fluid has two different temperatures causing differing densities. An example of natural convection is water being heated on a stove. The heat from the stove heats up the bottom of the water, causing the molecules to vibrate faster. When molecules vibrate, they expand and lose density, causing the warmer water to rise and the cooler water to sink. The cooler water will then heat up and rise to the top. The circular current this process produces is called a convection current and is responsible for many aspects of the weather.
The last method the world uses to transfer thermal energy is radiation. With radiation, objects can transfer thermal energy through a vacuum. This is the type heat transfer by which the sun warms the earth. In this process, thermal energy is transferred in the form of infrared rays. Though thermal energy can be transferred through radiation, we feel the heat when the infrared rays strike an object, like air, and cause the molecules to move faster, thus heating up.
