Soap Powered Boats (PW + DS Pepper)

Adult supervision: liquids not for drinking

Materials

• Water (not included)
• Tray, sink, or long container to hold water (not included)
• 3 3-D Printed Boat Models
• Pepper
• Blue Dish Soap
• Pink Dish Soap
• White Vinegar
• 91% Isopropyl Alcohol
• Pipette
• 6 Cotton Swabs
• Styrofoam/Paper Plate
• Scissors

Procedure

  1. Fill a tray, sink, or long container with water.
  2. Sprinkle pepper over the surface of the water. Float the 3 boat models in the water (ensure that no water is on top of them).
  3. Using a cotton swab, pick up a small amount of dish soap and place it in the water behind each boat or in the middle of the ‘keyhole’ on the boat with the hole in the center. What do you observe? Why do you think the boats and pepper reacted the way that they did?
  4. Try using the pipette instead of the cotton swab. Is the result the same?
  5. Repeat step 3 with the other 3 liquids (Note: the water may need to be replaced with clean water). Which liquid works best? What does this tell you about the liquids? (See ‘Science Behind it!’) It may help to sprinkle more pepper over the water between each trial so that you can see what is happening.
  6. Try applying the liquids along the back edge of the boats, then placing them in the water. What do you notice?
  7. Using the scissors and the plate, design your own boat and cut it out of the bottom of the plate. Does it work as well as the other boats?

Science Behind it!

You have just propelled your way to the science behind it! Ready, set, go!
When you place pepper in the water, it just sits on the surface of the water. Why would it not sink to the bottom of the water? Pepper is hydrophobic, when means that water is not attracted to it. You think of “phobic” meaning “fear of” so the molecules are running away because they are afraid. Therefore pepper cannot dissolve in water. Why do they float on top? Molecules like to cling to each other, this is what is known as surface tension. As soon as you start placing dish soap on the water, what happens? The pepper goes to the side, fairly quickly because the dish soap is able to break down the surface of the water. As the soap moves into the water, causing the surface tension to change, the water no longer wants to cling together, the pepper does not want to float on top anymore. However, the water molecules still want to keep the surface tension going, so they pull back away from the soap, which does what to the pepper? Experiment with the different types of liquids? What happens each time? Which boat goes the fastest? Have fun propelling your way to the finish line!