Does cold radiate outwards? What’s the process by which a hot object becomes cold?
In: Physics
Cold is the absence of heat. Heat always flows from a hot region to a cold region. That is an idea so basic that they had to go back and make it a law after they had already named the first law (energy can not be created or destroyed) so the law that heat flows from hot to cold is called the “zeroth law of thermodynamics”
So we know that a hot object will give its heat to all the cold things around it. There are three ways that heat can move. It can be conducted from one object to another just because the objects are touching. Also, heat will be conducted from the hot part of an object to the cooler part of the same object. To feel this in action, get a copper wire and heat one end. Copper is a great conductor of heat: you will feel the cool end warm up quite quickly.
The second way heat can move is by convection. That is when a fluid, like air or water, flows past the hot object and picks up heat as it goes by. A hot fluid can also transfer heat to a cooler object that it is flowing past. In fact a car radiator is a good example of convection: hot water flows through the tubes of the radiator and heats up the metal. Then cool air flows over the outside of the radiator and picks up the heat and carries it away. Convection inside and outside.
The third way to transfer heat is by radiation, and oddly, a radiator does not use this method. Radiation is the way heat from the sun gets to Earth even though the space between is a vacuum. The heat is carried by electromagnetic waves, including good old light, and waves not quite long enough for humans to see, called infrared waves. Light can travel through a vacuum, and it carries the heat with it. It is worth noting that to get any decent amount of heat by radiation, the hot object has to be really hot.
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