Upside down water cup experiment | Fizzics Education


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Upside-down water cup

Upside-down water cup

Follow FizzicsEd 150 Science Experiments:

You will need:

  • One cup of water full to the brim with water.
  • One piece of card, larger than the cup rim. You can also use paper.
  • An area that you can get wet.


Upside down water cup science experiment - materials needed
1 Upside down water cup science experiment - placing paper on top of a filled cup of water

Fill your cup with water (try different levels each time!).

Gently place a dry card on top of the cup, making sure there is good contact over the cup rim.

If doing this inside have a tray, bowl or plate to catch the water spilling

2 Upside down water cup science experiment - water staying in an upturned plastic cup

Carefully turn the cup upside down, keeping upward pressure on the card with your hand.

When the cup is upside down, let go of the card.

Can you explain why the water doesn’t come out?

3 A blue balloon in bell jar under lights
4 Teacher showing how to do an experiment outside to a group of kids.

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– Help students learn how science really works

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5 A man holding a soda can with tongs and a bunsen burner heating the can base

Get the Unit of Work on Pressure here!

Want to dive into air pressure?

Get the 60-minute video + PDFs + curriculum links for your class here!

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Why Does This Happen?

Air molecules are constantly pushing into things, in every direction imaginable. In other words, air has pressure. If you look at your thumbnail, you have the equivalent of around 1 kg of weight pushing down on that body part alone!

Inside the cup there was no air, so the weight inside the cup was coming only from the water. Depending on the size of your cup, the weight of the water may have been around 250g. The air below the card was pushing up into the card. The upwards air pressure was much greater than that of the pressure of the water pushing towards the ground – keeping the water in the cup.

Variables to test

More on variables here

  • Try progressively larger cups. How big can you get? Try a bucket!
  • Does it matter which type of liquid is used? Try a variety of liquids of different densities.


Knowledge of how pressure works allow engineers to design structures. Airlocks, for example, are used by deep-sea divers leave and enter their submersible vehicles whilst completely underwater. The air inside the airlock is compressed at the same pressure as that of the water outside the airlock. The equal pressure stops the water from entering the airlock. NASA even uses airlocks during their underwater training!

A man with a glove above a liquid nitrogen vapour cloud

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