Soap Powered Boat
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Things You Will Need
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Instructions
If your boat is lightweight (not too many decorations), it should float and move forward quickly when you put the first few drops of soap into the notch.
Explore
Do you have a hypothesis on why the boat moves?
After the boat has stopped, repeat the experiment a few more times in the same pool of water and see what happens.
Are you able to prove or disprove your hypothesis?
Why
The boat moves because the soap alters the water’s Surface Tension.
Water molecules (the tiny little pieces of water) tend to stick to one another. The way they want to stick together is called Cohesion.
On the surface of the water, water molecules are more attracted to other water molecules than to the air resulting in Surface Tension.
In this experiment, the “boat” can float on water due to this surface tension.
Water has high surface tension, which means the molecules are pulling each other on the surface very strongly.
Soap (a Surfactant) breaks down water’s surface tension by giving water molecules something else to be attracted to.
When a drop of soap is placed in the notch, the surface tension of the water in that small area is reduced.
The high surface tension in the rest of the surface of the water pulls the water away from the area with low surface tension.
Thie boat moves forwar but, after repeating the experiment several times, the boat stops moving despite adding more soap.
By then, the surface tension in the entire pool of water has been broken.
When the surface tension difference between the front and the back of the boat disappears, the water will not be pulled and the boat will not move.
How can you make the Boat move forward again?
- Cut the styrofoam plate or cardboard into the shape of a boat.
- At the end of the boat, cut a small notch.
- (Optional) Decorate the boat how you want.
- Fill the container or the tray with a thin layer of water.
- Place the boat in the water.
- Using the toothpick or pencil, put a drop of liquid soap into the notch at the end of the boat.
- Watch what happens to your boat!
If your boat is lightweight (not too many decorations), it should float and move forward quickly when you put the first few drops of soap into the notch.
Explore
Do you have a hypothesis on why the boat moves?
After the boat has stopped, repeat the experiment a few more times in the same pool of water and see what happens.
Are you able to prove or disprove your hypothesis?
Why
The boat moves because the soap alters the water’s Surface Tension.
Water molecules (the tiny little pieces of water) tend to stick to one another. The way they want to stick together is called Cohesion.
On the surface of the water, water molecules are more attracted to other water molecules than to the air resulting in Surface Tension.
In this experiment, the “boat” can float on water due to this surface tension.
Water has high surface tension, which means the molecules are pulling each other on the surface very strongly.
Soap (a Surfactant) breaks down water’s surface tension by giving water molecules something else to be attracted to.
When a drop of soap is placed in the notch, the surface tension of the water in that small area is reduced.
The high surface tension in the rest of the surface of the water pulls the water away from the area with low surface tension.
Thie boat moves forwar but, after repeating the experiment several times, the boat stops moving despite adding more soap.
By then, the surface tension in the entire pool of water has been broken.
When the surface tension difference between the front and the back of the boat disappears, the water will not be pulled and the boat will not move.
How can you make the Boat move forward again?