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Air pushes less on Mars

Air and fluids · level 3, lesson 6 of 6

A question to start

On Earth, the air can push water about 10 metres up a very long straw. How high could the thin air of Mars push it?

The idea

On Mars, there is far less air above each square metre, so the air pressure is far lower: on average, about 160 times less than at the seaside on Earth.

That changes everything air pressure does:

  • Straws: on Earth, air can push water about 10 metres up a straw. On Mars, only about 17 centimetres.
  • Suction cups: the Mars air would push a suction cup on only very weakly.
  • Sealed bags: a bag of crisps packed on Earth and taken outside on Mars would puff up hugely, and burst.
Earth: 10 mMars: 17 cmjust a stub
Air pressure Mars Earth
Average at the ground 636 Pa 101,400 Pa
Air above each square metre about 170 kg about 10,300 kg
How high air can push water up a straw about 17 cm about 10 m

A pascal (Pa) is a unit of pressure. You will meet it properly later.

Worked examples

1. How many times less? \(101{,}400 \div 636\) is about 160. So Mars's air pushes about 160 times less hard.

2. The straw. On Earth, air pushes water about 10 metres up. On Mars, two things change: the air pushes much less, but the water is also lighter, because gravity is weaker. Together, the water only goes up about 17 centimetres.

3. A space suit. Because Mars's air pushes so weakly, people there need suits that hold air in and push on their bodies, like Earth's air does.

Try it

  1. Is Mars's air pressure higher or lower than Earth's?
  2. About how many times lower?
  3. How high could air push water up a straw on Mars?
  4. What would happen to a sealed bag of crisps from Earth if it were taken outside on Mars?
Answers
  1. Lower.
  2. About 160 times.
  3. About 17 centimetres.
  4. It would puff up hugely and burst.

Common mistake

"No air means no pressure, so Mars has none." Mars does have air, and air pressure. It is just very small.

Where it leads