Thermal Physics


How does clothing keep us warm?

Our skin is cooled primarily by convection currents in the air. Clothing, especially wool, traps air in small pockets, which reduces or eliminates convection. There can still be conductive cooling through the cloth, but cloth is a good insulator.

Home insulation, like styrofoam panels, fibreglass or blown-in cellulose act like clothing in reducing heat transmission by convection. Home insulation is rated by its R value of resistance to energy transfer. R is the inverse of conduction: R =1/U.

Air pockets within snow and ice function as excellent insulators. Many small mammals build snow dens to keep themselves warm, thereby taking advantage of the insulating properties of the snow. Natives of the Arctic build igloos that also keep the inhabitants warm by reducing loss by convection.

Many farmers protect their crops during sub-zero temperatures by spraying water on the crops, and when the water freezes, the plants are insulated by the poor conductive properties of the ice.

A tile floor feels cooler than a carpeted floor because tile is a better conductor, that is, mover, of heat. Both materials are actually the same temperature; however, because tile is a better conductor of heat than carpeting, when your hot foot makes contact with the tile it heats the top layer and the heat flows quickly through the tile. That makes the tile feel cool to your foot. The carpet is a poorer conductor. The top layer can remain warm while the lower layers stay cool. Much less heat flows from your foot to the floor, so the carpet feels warmer to your foot. This is another example of heat flow by means of conduction.


This is a web preview of the "The Handy Physics Answer Book" app. Many features only work on your mobile device. If you like what you see, we hope you will consider buying. Get the App