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Name: Abdul H.
Status: student
Grade: N/A
Location: N/A 
Country: N/A
Date: 12/15/2005


Question:
A soap powered boat is a small boat that is made from polystyrene. To move it, I put a small piece of soap so that it can reduce the surface tension at the back of the boat and the boat can move. It would be simpler if we could think of this thin elastic layer like a balloon. Putting soap is like popping the balloon. You break the surface tension; the thin elastic layer breaks and pulls away to the sides. If there is something floating on these water particles, like the boat, it goes along for the ride.However I have done the experiment by using non detergent and detergent soap. The result that I obtained was the detergent soap has give the highest average velocity to the soap powered boat compared to the non detergent soap. Could you give the reason due to the result above.


Replies:
Abdul,

I think you have already stated the answer yourself. It is not so much the soap that is breaking the surface tension and propelling your boat, as the detergent. Detergent has 2 distinct effects to help cleaning; Firstly it tends to attach to and surround grease, causing it to 'bead up', and secondly it breaks the surface tension of water having the opposite effect to help the water rinse dirt away more effectively.

While non-detergent soaps may still be able to propel your boat, they do not have anywhere near the effectiveness.

Ryan Belscamper



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