You will believe a coin can fly

The next time you're bored in a coffee shop, here's a little something to do. All you need is a coin, a straw, a cup, and a willingness to be made the object of many admiring looks — for you are the pennymaster.

Making a penny hop has been done in all kinds of situations, but most of them involve a cup. Sometimes the penny is placed on the rim of the cup and will hop over the far rim of the cup. Sometimes the cup is tilted just slightly upwards on a table, the penny is placed in front of it, and the penny hops up into the cup. Whatever happens, the penny briefly takes flight.


All you need to do is take a straw and blow a short jet of air above the penny. In comes Bernoulli's Principle — which states that if air is set in motion on one side of an object, it will cause a drop in air pressure. The still air on the other side of the object will stay at a steady pressure. So the moving air from the straw will lower the air pressure on one side, but the pressure on the other will stay the same, and the penny will experience an overall push upwards. It will rise up and "hop".

Practice a few times, and you can get some very dramatic jumps from the penny. Also annoyed looks from the counter staff.

Image: PD Photo.

[Via The University of Iowa, Josh Klug]


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