Make a simple dish soap powered boat and watch it go.
- liquid soap
- rectangular baking dish or aluminum pan
- thin sheet of plastic or aluminum foil or construction paper
- fill the baking dish half full of water
- cutout the sheet of material in the shape of a flat boat about 7 cm long and 5 cm wide (see Fig. 1)
- make sure the sheet is smooth and flat
- place the boat on the water on one side of the baking dish
- now put only one drop of dish soap at the little notch at the end of the boat.
Observation and Results:
- What did you observe?
- What happens if you try to add another drop of soap?
- does the shape of the boat matter?
When the soap is placed behind the boat, the soap wants to spread quickly throughout the water. The only direction the soap can go is out the back of the boat (where the slot is). This creates a force that pushes the boat forward. Why? According the Newton’s 3rd law, for every action there is an equal and opposite reaction. Once past the back of the boat, the soap disperses across the entire surface of the water and in a short time the surface tension of the water is broken.
- Instead of foil, try a thin plastic sheet or paper or cardboard or a plastic fastener for a bread bag
- Try different widths and shapes of the notch on the back of the boat.