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Coin Tower

Use stacked coins as an immaculate kids’ science demonstration in inertia, friction, and movement.

When it comes to scientific muses, Sir Isaac Newton is definitely near the top of our list. Our favorite laws to break involve physics, movement, and motion! That’s why we came up with the Coin Tower demonstration. Using a butter knife, you’ll remove the bottom coin from an entire tower of coins. What’s the secret? Perform the project to find out!

Experiment Materials

  • Coins
  • Butter knife
  • Adult supervision

Experiment

  1. Stack the coins into an even and straight tower.
  2. Use the dinner knife to swipe a coin out from the bottom of the tower.
  3. See how many coins you can swipe out before the tower topples!

How Does It Work?

The key to safely removing a coin from from the bottom of a stack comes from friction and inertia. Inertia comes from Newton's first law of motion, stating that an object in motion (or at rest) tends to stay in motion (or at rest). This means that the balanced coins wants to stay in their stacked position, in the spot they are stacked. However, when you attempt to remove the bottom coin, you apply an outside force that causes the stack of coins to topple over.

This is where friction becomes a factor. There is friction between the bottom coin and stack above it. There is so much friction that the bottom coin brings the next coin with it, that coin drags the next coin, and so on.  To overcome the amount of friction, you swing the knife at the bottom of the stack. This process is fast-moving, but there is plenty of force to remove the bottom coin. The amount of force applied to the coin is enough that the friction isn’t allowed to tip the tower over. Instead, the tower drops, almost perfectly, into the spot that it was before.