Water drops riding on steam
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Materials needed:
Stove
Frying pan
Spoon
Water
Oven mitt
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In this experiment you will observe what happens when a drop of water comes in contact with a hot metal surface.
Turn a heater to a high setting for about 10 minutes to allow it to become hot. Be careful not to touch the heater. Add a drop of water carefully to the heater. Do not add more than a drop of water at a time to the heater. Add more drops of water and observe their behavior. Turn off the heater and allow it to cool.

The boiling point of water, 212°F (1OO°C), is the temperature at which liquid water is changed to water vapor (steam). Since the temperature of the heater is probably more than 400°F (204°C), you might expect that a drop of water would instantly change to steam. Instead, the drop lasts a long time in the heater. You probably observe that the drop of water placed on the heater seems to skate around in the heater as it makes a sizzling sound. This surprising behavior of water drops on a hot surface is called the Leidenfrost effect.
As the drop of water comes in contact with the metal surface, the outer layer of the drop begins to vaporize (change from a liquid to a gas). This water vapor provides a layer of gas upon which the water drop floats. This gas also provides a barrier to the flow of heat from the heater to the cooler liquid water. As a result, the water drop does not immediately vaporize but instead may take several minutes to change completely to water vapor. The liquid changes to steam, and the drop gradually disappears.

In the Leidenfrost effect, only that part of the drop that touches the hot surface changes to steam. Heat does not flow through gas as well as it does through water. Therefore, the drop is insulated from the hot surface by the steam coming off the drop.

Have you ever seen pictures or movies of people walking across glowing hot coals? (Do not try to touch or walk on hot coals.) How do firewalkers keep their feet from getting burned? Let's discuss several reasons: First, the layer of coals has a high temperature, but the red-hot layer is quite thin. Therefore the total amount of heat energy along the top of a suitable bed of coals is not high. Second, tissue in feet is mostly water, and water can store a lot of heat energy. Therefore, a firewalker's feet can absorb a certain amount of heat without getting burned. Third, the Leidenfrost effect helps insulate the firewalker's feet. Perspiration or moisture on the feet changes to steam and absorbs energy. As you know from your experiment, this steam can act like a layer of insulation. This gas underneath helps protect feet from the effects of the heat. However, even though we understand the science of firewalking, it should only be done by those specially trained in this unique activity.