Heat can move from one place to another. There are three ways in which this can happen: by conduction, convection, and radiation. Both conduction and convection can occur only if there is matter present, because they involve moving molecules. Radiation, however, include heat traveling through vacuum on empty space. When a solid object is heated, the molecules close to the source of the heat start to vibrate more rapidly than when the object is cool. These energized molecules collide with nearby molecules and pass on some of their energy to them. These collisions continue, and eventually the whole object becomes heated as more molecules tend to vibrate more rapidly than before. This process by which heat spreads through solid objects is called conduction. In general, when two objects are brought in contact with each other, the object with greater temperature will transfer heat to the one with lower temperature. This is again due to conduction ---- the molecules at the surface of the hotter body in contact will transfer kinetic energy to the molecules at the surface of the other body, thus, heating it up.

      For example, consider the time that you pour boiling water into a cup with a metal teaspoon in it. After some time, you feel the teaspoon handle, which is not even submerged in the water, warming up. That's because heat from the water transferred to the spoon and spread all over until  the molecules of the spoon handle was "energized" as well. Some materials, especially metals, are good conductors of heat. Materials that do not conduct heat well such as rubber, wood, and glass are called insulators.

      Gases and liquids (except mercury, which is a liquid metal) are poor conductors of heat. Heat travels through them by convection. For example, when a saucepan of cold water is heated, the water near the heat source becomes warmer than the rest of the liquid; it expands and becomes less dense than the water above. This causes the water below, near the heat source to rise and the water above which is denser to sink to the bottom to take its place. Eventually, the water below gets heated up again and the water above cools down since it got farther away from the heat source. This difference in temperature causes a difference in densities, in a way that warm water is less densr than cold water. And this causes movement of water molecules within the water sample because warm water, which is less dense, always rises above cold water which is denser. These movement is called convection currents. Convection is a way of transferring heat all throughout the material by making the molecules move through distances, carrying the heat energy with them. In effect, convection is heat transfer by mass transport.

      In the earth's atmosphere, huge convection currents cause winds to blow. When the sun warms the earth, the air above the land is heated. As the warm air rises, cooler air rushes in to take its place. Convection currents in the oceans transfer heat from the hot regions around the equator to cooler parts of the world.

      The sun radiates off heat and a portion of this reaches the earth after traveling 147 million km through empty space. Heat radiation was discovered in 1800 by William Herschel an English astronomer. He noticed that when sunlight passed through a prism and was split into its component colors, the red light gave off heat, which he detected with a thermometer. He concluded that the sun's rays carried energy other than light, and he named the rays of heat energy infared.

      Infared rays are electromagnetic waves equivalent to heat. It travels through empty space at the speed of light. Heat therefore, may also travel from one point to another in the form of electromagnetic waves called infared rays. This method of heat transfer is called heat radiation.