Have you ever seen a boat powered by soap? No? Now you can make one!

What you need:

Thick, smooth card paper or cardboard, a tub, water, liquid dishwashing soap and a toothpick.

What to do:

1. To make your boat, cut the card into the shape of a rectangle. Then diagonally trim off the upper corners to make a triangular head. To make the rear end, cut out a small triangle inside like the one shown in the figure:

2. Fill the tub with water.

3. Dip the toothpick into the liquid soap. Use the toothpick to delicately coat the sides of the rear triangle with the soap.

4. Now place the boat in the water.

What happens?

Once the boat touches the water, it shoots across the water for a few seconds.

Why?

The answer lies in surface tension.

Surface tension is the force that keeps the molecules of a liquid bound to each other at the surface of the liquid. This makes the top of a liquid act like an elastic sheet, one you need to push through if you want to go deeper into it. Try dipping your finger into water and you’ll understand. Soap is a surfactant. A surfactant is a substance which can reduce the surface tension of a liquid. By that it means, that it can loosen the bond between the molecules at the surface of the liquid. That’s exactly what the soap does.

Once the boat is put into the water, the soap on its rear end starts separating the surface molecules and reducing the surface tension. However, there is no soap on the front part of the boat. Which means a sort of difference is created in the surface tension between the front and back zones. The higher surface tension zone pulls the boat towards itself and the boat shoots forward! Once the soap spreads through the water, the surface tension equals out and the boat stops moving. To make it shoot forward again, you’ll need a tub of fresh water.

Picture Credit : Google

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