WHAT YOU NEED:
Hand sanitizer - that's it!
WHAT YOU DO:
- Pour a small amount of sanitizer into your hand and rub your hands together.
- Notice what happens - your hands feel colder and the liquid is going away.
- Repeat a second time by pouring a small amount of sanitizer into your hand and rub your hands together.
- This time wave your hands around in the air and notice what happens. Your hands feel even colder when you wave them around than they do when you hold them still.
WHAT'S HAPPENING:
The sanitizer comes out as liquid, but after you rub your hands together, it starts to disappear. It's not all soaking into your skin that quickly; it's evaporating! Changing from a liquid to a gas (evaporating) requires energy/heat to happen. It takes that energy from the air around it and from your hands. So while the evaporation is happening, your hands feel colder. Evaporating is a cooling process, which is why you sometimes hear us say "rain-cooled air." If the rain is evaporating, it cools the air around it. When you add wind into the mix (by waving your hands around), you feel the cold even more. This can help explain why wind chill on a cold winter day is so important. When your body is already losing heat and you add wind into the equation, you lose heat faster like what happened here with the sanitizer.
DISCUSSION IDEAS:
What do you feel during this activity?
Why do you think that's happening?
Where did the liquid go?
