How is heat transferred

Learning Lesson: Melts in your bag, not in your hand. Conduction is the transfer of heat energy from one substance to another or within a substance.

Have you ever left a metal spoon in a pot of soup being heated on a stove? After a short time, the handle of the spoon will become hot. This is due to transfer of heat energy from molecule to molecule or from atom to atom. Also, when objects are welded together, the metal becomes hot the orange-red glow by the transfer of heat from an arc. This is called conduction and is a very effective method of heat transfer in metals. However, air conducts heat poorly.

Convection is the transfer of heat energy in a fluid. This type of heating is most commonly seen in the kitchen with a boiling liquid. Air in the atmosphere acts as a fluid. The sun's radiation strikes the ground, thus warming the rocks. As the rock's temperature rises due to conduction, heat energy is released into the atmosphere, forming a bubble of air which is warmer than the surrounding air. This bubble of air rises into the atmosphere. As it rises, the bubble cools with the heat contained in the bubble moving into the atmosphere.

As the hot air mass rises, the air is replaced by the surrounding cooler, more dense air, what we feel as wind. These movements of air masses can be small in a certain region, such as local cumulus clouds, or large cycles in the troposphere, covering large sections of the earth.

Convection currents are responsible for many weather patterns in the troposphere. The more motion the atoms or molecules have the more heat or thermal energy they will have. This is an animation made from a short molecular dynamics simulation of water. The green lines represent hydrogen bonds between oxygen and hydrogen. Notice the tight structure of water.

Hydrogen bonds are much weaker than covalent bonds. However, when a large number of hydrogen bonds act in unison they will make a strong contributory effect. This is the case in water shown here. Liquid water has a partially ordered structure in which hydrogen bonds are constantly being formed and breaking up. Because of the short time scale on the order of a few picoseconds few bonds What is temperature? From the video above that shows movement of atoms and molecules it can be seen that some move faster than others.

Temperature is an average value of energy for all the atoms and molecules in a given system. Temperature is independent of how much matter there is in the system. It is simply an average of the energy in the system.

Heat can travel from one place to another in three ways: Conduction, Convection and Radiation. Both conduction and convection require matter to transfer heat. Yet every process involving heat transfer takes place by only three methods:.

Figure 1. In a fireplace, heat transfer occurs by all three methods: conduction, convection, and radiation. Radiation is responsible for most of the heat transferred into the room. Heat transfer also occurs through conduction into the room, but at a much slower rate. Heat transfer by convection also occurs through cold air entering the room around windows and hot air leaving the room by rising up the chimney. We examine these methods in some detail in the three following modules.

Each method has unique and interesting characteristics, but all three do have one thing in common: they transfer heat solely because of a temperature difference Figure 1. Figure 2.