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What does air weigh?

So, what does air weigh? It’s weightless isn’t it?

You walk around, you can’t feel it pushing down on you…Air is invisible but it’s not weightless, it’s a mixture of different gases made up of lots of different molecules, all of these have mass.

What is Air Pressure?

We call the force exerted by air – “Air Pressure”- it’s the weight of all the air molecules pressing down on the Earth. Scientists use the term one atmosphere to describe the pressure at sea level. The weight of the air at sea level is approximately 6.6 kilograms per square inch, so for every inch of our body we are carrying 6.6kg!

The reason we are able to move is because the pressure is equal on all parts of our body, we are not crushed by the weight of the pressure because there is equal pressure inside and out of our bodies. But, what would happen if this wasn’t the case? What if the pressure inside us was lower…let’s find out…

Let’s explore….

You’ll need two bowls of water (one warm and one icy cold), a towel and a bottle with a lid.

  1. Fill your bottle with warm water and leave for a couple of minutes

2. Empty out the water and pop the lid back on

3. Now place the bottle into the bowl of icy cold water- what happens to the bottle?

4. Pop the bottle back into the bowl of warm water- what happens now?

Why did the bottle get squashed?

When we add hot water into the bottle, the air inside warms up, increasing the air pressure. We then trap the warm air inside the bottle by putting the lid back on. By adding the bottle to the icy water we cool the air rapidly, lowering the pressure inside the bottle. This means the air pressure outside the bottle is greater than the pressure pushing back from inside the bottle so the bottle gets crushed. The same would happen to us if the pressure inside our bodies wasn’t the same as the pressure outside of it.

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