Conduction of Heat – Observing heat conduction within a metal rod.

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Thermal Conductivity
When an object is heated, thermal energy moves from hot to cold. This occurs as the particles within the object collide. In order for heat to move from one region to another, it must pass through all of the particles in between. The time it takes for this to occur is different in different materials and different states of matter. The ability of a material or matter to transfer thermal energy is called thermal conductivity.

Some materials allow heat to pass through them more easily than others. Materials that allow heat to pass through them easily are called good conductors of heat. The metal used to make the pot is a good conductor of heat. It allows heat to flow easily from the hotplate to the food.

Materials that do not allow heat to pass through them easily are called poor conductors of heat, or heat insulators. The plastic handle on the pot is a poor conductor of heat. Heat cannot flow through the plastic easily, so it does not get as hot as the metal.

Wool and fabrics such as fleece are good heat insulators. They are often used to produce clothing to keep people warm.

Generally, matter in a solid state are better conductors of heat than matter in a liquid state. This is because the particles in solids are more tightly packed together than the particles in liquids. Similarly, liquids are generally better conductors of heat than gases.

Transfer of Thermal Energy – Conduction
Thermal energy moves in three main ways – conduction, convection and radiation.

Think again how heat moved in the metal rod placed on a fire. The thermal energy moved from the hot part of the rod to the cooler part of the rod. This movement of heat within an object is called conduction. Conduction also occurs when objects are touching. If you were to hold the cool end of the rod, before too long it would feel warm as thermal energy moves by conduction to your hand.

Heat transfer from a hot cup to your hands and cooking a piece of fish in a pan are also examples of conduction.