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Ever wondered what would happen to your body in space? This activity will give you some idea. It shows how a marshmallow expands dramatically when normal atmospheric pressure is reduced, so students can understand what would happen to a human body in its place!

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Follow these steps…

You will need: a glass bottle, small marshmallows, a drink vacuum pump and its rubber stopper

  1. Put four or five marshmallows into a glass bottle.
  2. Push the rubber stopper into the bottle, put the pump on top and use it to remove the air until you see a change in the marshmallows.
  3. Look at what has happened to your marshmallows.
  4. Take the rubber stopper out of the bottle and watch your marshmallows closely.
  5. Look at your marshmallows now!
  6. See what happens if you try other things in the bottle.

Think and talk about…

  • What do you see happening?
  • What makes the marshmallows expand?
  • What do you think might happen to humans in a similar environment, such as in space?


  • What happens if you use a plastic bottle instead of a glass one? Why do you think there’s a difference?
  • Try putting other items in the bottle – such as grapes, shaving cream or jelly sweets – and see what happens. Was it what you expected?

Did you know?

If your body were exposed to the near vacuum of space, your blood would quickly boil and your eyes would explode.

What’s the science?

The atmosphere stretches for a few hundred kilometres above our heads. The weight of all that air pushes on every surface. Trapped inside marshmallows are thousands of tiny bubbles, and the air inside those bubbles is at atmospheric pressure – the same as the air outside. Reduce the pressure around the marshmallows, by removing air from the bottle, and the air pressure inside those pockets is now greater than the air pressure outside, so the marshmallows puff up dramatically. Allow air back into the bottle, and atmospheric pressure squashes the air pockets again, so the marshmallows shrink back to normal.

Science in your world

Popcorn kernels expand in a similar way to the marshmallows in the activity – but in that case it’s because of the pressure inside the kernels becoming much greater than atmospheric pressure, as water inside them turns to steam and expands. A vacuum cleaner makes an area of low pressure, creating suction as atmospheric pressure causes air to rush in, bringing dust and debris with it.