Science Sunday for Kids – Thermal Expansion (The Coin Jumping Trick)

Science Sunday for Kids – Thermal Expansion (The Coin Jumping Trick)

Welcome to another instalment of Science Sundays for kids! This quick little experiment is one of Molly’s favourites. Not only because it’s “magic” but because it’s easy enough that she can do the whole thing by herself. I love also love it because there’s no mess to clean up! The only thing you need to do ahead of time is put your bottle in the freezer so it’s good and cold when you are ready to do the experiment.

The Coin Jumping Trick


  • One glass bottle with a small mouth (like a wine bottle)
  • One quarter
  • Water

coin jumping trick


Put your bottle in the freezer well ahead of time – at least an hour (I just leave one in there all the time). You need it to be good and cold.

Dip your finger in the water:

science for kids

Now run your finger over the top of the opening on the bottle to get it wet:

thermal expansion experiment

Now place your quarter on top, covering the opening:

coing jumping trick

Make sure the quarter is centered and covering the entire opening!

Now place your hands firmly around the bottle and watch the magic!


How does it work?

Thermal expansion baby! Thermal expansion happens when heat is applied to matter. When you place your warm hands around the cold bottle the matter (in this case the air in the bottle) changes its volume – it expands. When you wet the top of the bottle and then put the quarter on you created a seal. The warmed, expanding air breaks that seal and pushes the quarter up to escape.

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