Conductors and insulators at work
Metals such as copper and silver are very good conductors. Diamond is the best natural conductor of heat of all. Wood, plastic, polystyrene and air are poor conductors, so they are insulators. We choose each material for its job. Cooking pans are made of metal so that heat passes quickly from the stove to the food, but their handles are plastic or wood so that heat does not burn the hand. Hollow clay bricks and polystyrene boards in walls trap air and cut the heat flow, so a house stays cooler in summer and cooling costs less. The computer and the phone need the opposite: a metal plate or paste carries the heat away from the chip. Air conducts so little that double glazing, with a layer of air or gas between two panes, also cuts heat loss. Insulating a building saves energy, which saves money and lowers pollution. But we should not say that any material is a perfect insulator: every material lets some heat through.
| Use | Material | Why |
|---|---|---|
| pan base | metal | passes heat quickly to the food |
| pan handle | plastic or wood | stays cool to hold |
| house wall | hollow brick | traps air, slows heat flow |
| phone chip | metal plate | carries heat away |
Which cup keeps warm longest? With a grown-up, fill three equal cups with the same amount of warm (not hot) tap water. Wrap one in a towel, one in foil and leave one bare. Read the temperature of each after 20 minutes and compare. Describe what you see. Write which material was the best insulator, and say which factors you kept equal.