Radiation, for example, is the only method by which internal energy can be transferred through a vacuum. So when a hot object is near a cold one in space, 100% of the heating is by radiation. All of the energy we receive from the Sun comes to us that way.
Convection heating involves the mixing of fluids (liquids and gasses) of different temperatures. No convection, therefore, occurs between or within solids. A hot copper cube in contact with a cold iron cube would, for example, heat it primarily by conduction (and some radiation).
Conduction occurs when the vibrating atoms of the copper transfer some of their energy to the iron atoms they come in contact with. The energy lost by the copper atoms results in a lower temperature, while the energy gained by the iron atoms translates to a higher temperature for that object.
All three heat transfer methods can occur simultaneously, or only one of the three might occur, depending on circumstances. A vacuum (Thermos) bottle is designed to minimized all three
forms of heat transfer--a vacuum reduces conduction, mirrored sides minimize radiation, and a tight lid minimizes cooling of the air above the liquid's surface by convection.
Answered by: Paul Walorski, B.A., Part-time Physics/Astronomy Instructor
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