Here’s a balancing game, but with a bit of practice you will always win! Why? Because you’ve set up a clever trick.
In this game, take turns to put drops of water on your coins. Whoever spills their water first, loses!
Without anyone seeing, put a very small drop of detergent on your index finger.
Keeping the detergent away from the coins, put both coins on the palm of your other hand.
Put their coin on the table and secretly touch the top face of the coin with detergent from your index finger.
Choose an eye dropper each. Suck up some water with your eye droppers and start playing. Take it in turns to place a drop of water onto your coin. If you managed to get detergent on their coin, you should win every time!
You might be surprised to find how many drops of water you can fit on a coin without it spilling. With care, you can pile the water millimetres high. This is because water ‘sticks’ to itself. Attraction between water molecules causes the water droplets to clump together in a larger blob.
Detergent contains surfactants, chemicals that battle against water clumping. A surfactant molecule usually has two parts. One end is attracted to water, and the other end is attracted to some other chemicals.
Surfactants tend to move to the water’s surface. This makes the water more attracted to other substances, including air. This new attraction balances against water’s natural clumping.
The result is that drops of water don’t hold together as tightly with a surfactant around. So the coin with detergent won’t balance as much water on top.
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