Allowing and Blocking Heat
In the last lesson, we learned that heat is the transfer of thermal energy. But does heat travel through all materials at the same speed? Definitely not! Some materials let heat pass through them very easily, while others block the flow of heat. This property determines whether a material is a conductor or an insulator.
Thermal Conductors
A thermal conductor is a material through which heat can flow easily and quickly.
How it works: In a conductor, the particles are packed closely together, and in the case of metals, they have free-moving electrons. When one part of a conductor is heated, the particles gain energy and vibrate rapidly. They quickly bump into their neighbors, passing the energy along. The free electrons in metals are especially good at this, acting like tiny messengers that rapidly carry thermal energy from one place to another.
Examples: Most metals are excellent thermal conductors. This includes copper, aluminum, iron, and silver.
Everyday Use: We use conductors when we want heat to travel. A cooking pot is made of metal so that the heat from the stove can travel quickly through the pot to cook the food inside.
Thermal Insulators
A thermal insulator is a material through which heat flows slowly or not at all.
How it works: In an insulator, the particles are either far apart (like in a gas) or they are held in a way that they cannot easily pass vibrations to their neighbors. Insulators are good at trapping heat.
Examples: Materials like wood, plastic, cloth (like wool), and rubber are good insulators. Gases, including air, are also excellent insulators, as long as the gas is trapped and cannot move to create convection currents.
Everyday Use: We use insulators when we want to stop heat from traveling.
The handle of a cooking pot is made of plastic or wood so that the heat from the pot doesn't travel to your hand.
We wear a woolly sweater in the winter because the wool fibers trap pockets of air. This trapped air is a fantastic insulator that stops your body heat from escaping into the cold environment.
A cooler or a thermos is designed with insulating materials (like foam, which is mostly trapped air) and a vacuum layer to prevent heat from entering (to keep things cold) or leaving (to keep things hot).
Think about touching a metal chair leg and a wooden chair leg in the same room. The metal leg feels colder, right? This isn't because it's at a lower temperature (they are both at room temperature). It's because the metal is a good conductor, so it rapidly pulls heat away from your hand, making your hand feel cold. The wood is an insulator, so it transfers heat away much more slowly.