Conduction

Conduction is the transfer of thermal energy with no overall transfer of matter. Conduction occurs within a material or between materials that are touching. To understand conduction, look at the Newton's cradle in Figure 5. When a ball is pulled back and released, you might expect all of the balls to move to the right after the impact. Instead, most of the kinetic energy is transferred to one ball on the end. Similarly, in conduction, collisions between particles transfer thermal energy, without any overall transfer of matter.

Recall that forces are weak among particles in a gas. Compared to liquids and solids, the particles in gases are farther apart. Conduction in gases is slower than in liquids and solids because the particles in a gas collide less often. In most solids, conduction occurs as particles vibrate in place and push on each other. In metals, conduction is faster because some electrons are free to move about. These free electrons collide with one another and with atoms or ions to transfer thermal energy.

Figure 5 Conduction is the transfer of thermal energy without transferring matter. This device, called Newton's cradle, helps to visualize conduction. After one ball strikes the rest, most of the kinetic energy is transferred to one ball on the end.