EasyChemistryHigh School (9–10)GeneralStates of Matter › Evaporation and CoolingConceptualBoard Exam
Why are cotton clothes better than polyester clothes on a hot summer day? …
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
- Why are cotton clothes better than polyester clothes on a hot summer day?
- Why does a wet cotton cloth on the forehead help to bring down a fever?
Need a reminder? The key ideaShow
Evaporation cools: the fastest particles leave, and the liquid takes the heat it needs from its surroundings, . At skin temperature each gram of sweat takes about . Power is heat divided by time, and .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) Cotton soaks up sweat and spreads it over a large surface, where it evaporates fast. The evaporation takes heat from the body. Polyester soaks up little sweat, so the sweat stays on the skin, evaporates slowly, and we feel hot and sticky.
Step 2. (b) The water in the cloth evaporates, and it takes its latent heat from the forehead. This carries heat away from the body.
Answer: (a) Cotton holds the sweat and lets it evaporate quickly, which cools us. (b) The evaporating water takes heat from the forehead.
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