Science | Science Experiment of the Week 10 | 303 - Obedient Coin

Now comes the trick. The dime is under the glass. You want the dime to be outside the glass, but you are not allowed to touch or move the glass.

This Week's Experiment - #303 Obedient Coin

These experiments are from Robert Krampf - The Happy Scientist

If you have been on this list for long, you know how much I like experiments that deal with food. I also like experiments that double as magic tricks. I have never been very good at high dexterity tricks, so the easy success of science based tricks makes them my favorites. To try this one, you will need:

a clear drinking glass
2 thick coins (US quarters or nickels)
1 thin coin (US dime)
a table covered with a table cloth or towel

Place the two quarters on the table far apart enough so that they will support the glass if it is turned upside down. Place the dime on the table between them. Turn the glass upside down and place it onto the two quarters.

Now comes the trick. The dime is under the glass. You want the dime to be outside the glass, but you are not allowed to touch or move the glass. You cannot stick anything under the glass. Because the glass is supported by the other coins, there is just enough room for the dime to slide under the edge and come out to you. Easy, right? All you need to do is convince the dime to do that. How?

It is really quite simple. Pretend that the table itches just in front of the glass. Use your fingernail to scratch the tablecloth, just as if it itched. Watch the dime carefully as you do this. The coin begins to slide towards you. Soon, the dime will be out from under the glass.

How does this work? The trick is the similar of the old trick of jerking the tablecloth out from under the dishes. As you scratch the cloth, you stretch it towards you. This moves the coin forward slightly. When you lift your finger to scratch again, the cloth snaps back. Because this movement is so quick, the coin does not move back with it. Inertia causes the coin to resist the rapid change in movement. With each scratch, the coin moves forward with the slower movement of your scratch, but is left behind with the faster movement as the cloth snaps back in place.

To make the illusion better, make a big deal about calling the coin, just as if you were calling a pet. Once you have impressed your friends with your magic trick, you can impress them again by explaining the science behind it. Have a great week.

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