Have you ever taken a spoon out of a mug of hot cocoa or tea or some other hot drink?
Did you find that the spoon was too hot to hold, so that you had to drop it?
Did you burn your fingers?
If you have never done this, don’t try it now.
But if you have done this, then you found out the hard way that heat can travel through some solid materials, such as metals. When heat travels in this way, we say that the heat is conducted. In the hot drink, the heat is conducted from the liquid into the metal spoon.
Why was the handle of the spoon so hot?
Atoms in the bowl of the spoon move faster and bump harder into each other as they heat up. The faster the atoms vibrate the hotter the spoon becomes. The atoms in the lower part of the spoon then bump into the metal atoms a little farther up the spoon. These atoms then bump against their neighbors even farther up and start them vibrating. Soon, all the atoms in the spoon are vibrating faster.
When the handle of the spoon is cold, the atoms in the metal vibrate slowly.
When the handle of the spoon is hot, the atoms vibrate quickly and bump into each other.
A material that allows heat to travel through it, like the metal spoon, is called a conductor. Some materials are better conductors of heat than others. Metals like iron, steel, and copper are good conductors. They also allow electricity to flow easily through them. Other materials, such as rubber, wood, glass, and some plastics, are poor conductors. A material that does not conduct heat or electricity easily is called an insulator.
Protection from heat and cold
Insulators are useful materials. The handle of a saucepan, for example, is often made of plastic or wood. This stops the conduction of heat from the pan to the handle. Fire fighters wear clothes made from another good insulating material called fiberglass. The fiberglass prevents the heat of a fire from reaching the fire fighter’s body.
Air is a good insulator, too. This is why we wear wool clothes to keep warm in cold weather. Wool traps plenty of air between its fibers. Special insulated underwear provides air spaces that help retain body heat. Can you think of any other ways m which we use insulators to keep away heat, or keep it in?