Cold Metal - "Cold" metal and "warm" wood may be the same temperature.

Cold Metal

 

"Cold" metal and "warm" wood may be the same temperature.

Your hand is not always a good thermometer. When you touch a variety of materials, some will seem warmer or colder than others, even when they are at the same temperature. 

 

• Various materials (metal, wood, Styrofoam, glass, plastic, cardboard, etc.) with one flat surface larger than the size of your hand.
• A thermometer (liquid crystal thermometer cards work well).

 

(15 minutes or less)

There is no actual assembly. Be sure that there are many different surfaces and that they are large enough for you to touch easily. Allow the materials to come to room temperature before you begin. 
 

(15 minutes or more)

Place your palms flat on the various surfaces and compare how cold they feel. Arrange the materials in order from cold to warm. Then place the liquid crystal thermometer, or regular thermometer, on each surface. Notice that all the materials are at the same temperature.

The temperature-sensitive nerve endings in your skin detect the difference between your inside body temperature and your outside skin temperature. When your skin cools down, your temperaturesensitive nerves tell you that the object you are touching is cold. An object that feels cold must be colder than your hand, and it must carry your body heat away so that your skin cools down.

Styrofoam and metal are two materials that work well for this Snack. They both start at room temperature and are both colder than your hand. They do not feel equally cold because they carry heat away from your hand at different rates.

Styrofoam is an insulator, a very poor conductor of heat. When your hand touches the Styrofoam, heat flows from your hand to the Styrofoam and warms the Styrofoam surface. Because this heat is not conducted away quickly, the surface of the Styrofoam soon becomes as warm as your hand, so little or no additional heat leaves your hand. There is no difference in temperature between the inside of your body and the outside of your skin, so the temperature-sensitive nerves detect no difference in temperature. The Styrofoam feels warm.

The metal, in contrast, carries heat away quickly. Metal is a good conductor of heat. Heat flows from your hand into the metal and then is conducted rapidly away into the bulk of the metal, leaving the metal surface and your skin surface relatively cool. That's why metal feels cool.

Metals will warm to above room temperature after just a few rounds of being touched. The surfaces should be allowed to cool for a few moments between each person's turn. It might be useful to have multiple metal samples. While you are using one sample, the extras have time to cool back to room temperature.

Posted in: Science Snacks