One of the fundamentals needed in science is an idea of what hot and cold are. Without this knowledge, working in a lab is difficult. So many things need heated or cooled in science labs and without the basics of hot or cold, these processes are difficult to complete.
This is a great experiment to show that even though something feels warm or cold to the touch, they may actually be the same temperature.
To begin, gather a variety of materials. Include items of metal, wood, Styrofoam, glass, plastic, and cardboard. Each item should have a flat surface that is larger than a hand. A thermometer, such as a liquid crystal thermometer card, is also needed. All the materials need to set out long enough to come to room temperature.
The students need to come and place a hand flat on each surface to compare how cold or warm each item feels. Then have the students list, on paper, the order of items from coldest to warmest.
Next, place the thermometer on the surface of each item and have the students record the actual temperatures. All the surfaces should have the same temperature.
Discuss with the students why some items feel cooler than others to the touch. The nerve endings in the skin are temperature sensitive, so they can differentiate between the temperature inside and outside the body. As the skin cools down, the nerves send the message to the brain that the item it is touching is cool. This occurs when the touched item is cooler than the body and it carried body heat away from the body. This causes the skin to cool down.
All the items start at room temperature, so they are cooler than the body. However, items like wood and Styrofoam feel warmer than glass or metal. Styrofoam and wood are insulators, so they conduct heat very poorly. When they are touched, the heat from the hand transfers to the wood and Styrofoam and warms their surfaces. The heat remains on these surfaces longer than the glass or metal. Because little heat leaves the hand, the surface feels warmer.
Metal and glass do carry away the heat quickly, they are good conductors or heat. When the hand touches these surfaces, heat travels from the hand to the metal. This means that the surface feels cool.
As metal only takes a few moments of touching to warm the surface above room temperature, it is a good idea to let it cool for a few seconds between each touch, or have several metal surfaces.