Wizard Science logoWizard Science
ExperimentsGamesSafetyAbout

← All experiments

The Upside-Down Water Card

Ages 6+ with an adult5 minutesMess: Medium: do it over a sink or bowl
Grown-ups: please supervise this experiment the whole time. Read the safety notes first.

Fill a cup, cover it with a card, flip it over and let go. The water stays put.

WOW FACT

Right now the air is pressing on every part of you. You don't feel it because the fluids inside your body push back just as hard.

🧰 What you'll need

A plastic cupAny cup from the cupboard works, as long as it isn't glass.
✔ You probably have this
WaterStraight from the tap.
✔ You probably have this
A postcard or stiff cardAn old birthday card or cereal-box card is perfect, as long as it's bigger than the cup's rim.
✔ You probably have this
A sink, bowl or trayWork over it in case the water escapes.
✔ You probably have this

✨ Want to go further? (optional)

Kids' science experiment kitLots more air-pressure and forces tricks in one box.
View on Amazon (amazon.co.uk)
Safety goggles for kidsGets children into good scientist habits, and keeps splashes out of eyes.
View on Amazon (amazon.co.uk)
Children's science experiment bookDozens of easy experiments for rainy days.
View on Amazon (amazon.co.uk)

💛 We may earn a small commission if you buy, at no extra cost to you. We only suggest things we'd use ourselves. How this works.

What to do

  1. Work over a sink or a large bowl.
  2. Fill the cup right to the brim with water.
  3. Slide the card over the top so it touches the rim all the way round.
  4. Hold the card flat with one hand and turn the cup upside down.
  5. Slowly take your hand away from the card.
  6. Try again with the cup only half full. What changes?

What's going on?

The air around us pushes on everything, in every direction. Pushing up on the card, the air holds it in place, and the water's surface tension helps seal the edge. It can fail sometimes, which is part of the fun: that's why we work over a sink.

Safety notes