How your body keeps warm and cool
Why do you shiver when you are cold, and sweat when you are hot?
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Explain
You shiver when you are cold.
You sweat when you are hot.
Your body works best at about 37 °C. A part of your brain acts like a thermostat.
When you are cold, your muscles shiver to make heat, and your skin sends less blood to the surface.
When you are hot, you sweat. As sweat evaporates, it carries heat away from your skin.
Sweating cools through evaporation, because liquid water needs a large latent heat to become vapour.
Blood vessels near the skin widen to lose heat by radiation and convection, or narrow to keep heat in.
Example: evaporating 1 g of sweat removes about 2400 J from your body.
- Your brain senses temperature
- Too cold: shiver
- Too hot: sweat
Want the full story?
The sim uses rough thresholds, but the real responses depend on clothing, wind, humidity and the person. Sweating works less well in humid air, since evaporation is slower. Normal body temperature also varies a little.
Try it at home
You need a little water.
You need: a little water.
Blow on a wet hand. It feels cool!
- Wet the back of one hand.
- Wave both hands in the air.
- Compare how they feel.
What's happening: water evaporating from your wet hand carries heat away, which is how sweat works.
Physics is life
Your body
You sweat when you run.
Daily life
We wear clothes to stay warm.
Nature
Dogs pant to keep cool.
Space
Space suits keep astronauts cool.
Quick check
Question 1 of 3
Words to know
Evaporation: A liquid slowly turning into a gas at its surface.
- Evaporation
- A liquid slowly turning into a gas at its surface.
- Temperature
- How hot or cold something is.
- Heat
- Energy moving from something hotter to something cooler.