This spooky idea takes almost no time, requires a dime and a bottle, and has the potential for creating quite a stir in your next magic show.  The idea is basically this: when you place a coin on a bottle, it starts dancing around. But there’s more to this trick than meets the scientist’s eye.


Here’s how you do it:


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Materials:


  • coin
  • freezer
  • plastic bottle (NOT glass)


Download Student Worksheet & Exercises


Remove the cap of an empty plastic water or soda bottle and replace it with a dime and stick the whole things upright in the freezer overnight. First thing in the morning, take it out and set it on the table. What happens?


Attention:  Magicians

If you’re a budding magician, here’s how to modify this experiment to use in your next show.  Get a glass container of soda and stick it in the coldest part of your fridge overnight. I know they are getting harder to find these days, but the glass will keep its temperature longer than plastic and enable you to do this trick.  In a pinch, you can refill a cleaned glass bottle from a previous use if you can’t locate a fresh glass soda bottle.


As soon as you’re ready to do your trick (practice first!), take it out of the fridge (have it in an ice chest if you’re on stage) and chug the whole thing. (You can ask your audience for help on this – you just want an empty cold bottle for the next part.)


When the bottle is empty but still cold, cap it with a wet dime. Place both hands on the bottle while you “wax eloquent” (make up an engaging story, like “North Winds, come have a taste of soda…”) but be sure to keep your hands on the bottle to warm it up. In about 20 seconds or so, the dime will click up and down, dancing around mysteriously.  Keep your hands on the bottle for another 20 seconds or so, and then set it gently on the table with it still dancing, and you’ll find it dancing right on without your hands being there.


How does that work? Was the bottle really empty when you placed it in the freezer? Actually, no… it had air inside of it. The air in the bottle shrank down a bit as it cooled, allowing more air to go into the bottle. When you remove the bottle from the freezer and cap it with the coin, you now have a bottle with more air in it than you started. The air warms and expands, pushing the excess air out the top, making the coin dance. Learn more about air with this Air Expands experiment.


Variations to try:

  • Is a plastic bottle or glass bottle better for this experiment?
  • What if you get the coin wet first?
  • Does a cold or warm coin work better?
  • What about a penny? Quarter?
  • Does the size of the bottle matter?

Exercises


  1. When a gas turns into a liquid, this is called:
    1. Convection
    2. Conduction
    3. Absorption
    4. Condensation
  2. When water boils, what happens to the bonds between its molecules?
  3. What is the best way to describe how the bonds between water molecules behave when in a liquid state?
    1. Solid bridges
    2. Rubber bands
    3. No bonds
    4. Brittle like chalk
  4. The crystalline shape of a solid is referred to as:
    1. a matrix
    2. a vortex
    3. a crystal
    4. a cube

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Comments

One Response to “Ghost Coin”

  1. tuhin_zaman says:

    we enjoyed this project very much thank you