Ellen had to build a boat for physics class. The boat had to be able to hold a 5 pound bag of sand and float for 1 minute, but when the sand was removed and the boat was filled with water it would sink (completely submerged). The teacher also specified that the boat couldn't be box shaped with square corners.
Think about it. The physics is pretty straight forward - although I had to explain it to Ellen about 10 times. What is the major criteria of the boats design to allow it to float carrying 5lbs of sand but sink when full of water?
Figured it out yet? No. Ok, I'll tell you. The hull of the boat has to be capable of holding a volume of water that weighs more than 5lbs. If it holds less than that ,then the boat won't sink. So we know that a gallon of water (or milk) weighs roughly 8.5 lbs. So any boat what would hold a gallon would float with 5lbs of sand and sink when filled with water. So with no specifications on the construction of the boat other than the limit on box shapes, we moved onto the next step.
What can I use to make this boat that won't dissolve in water and requires the least amount of work? A plastic gallon jug! Ellen and I drove to the grocery store and bought a gallon jug of juice. Nathan started drinking large volumes of juice while Ellen cut a hole in the side of the jug large enough to allow the sand to be loaded. We tested it in the kitchen sink and Voila! Floated with a 5 lb bag of sugar (conveniently packaged in that size already) sank like a stone when filled with water. After one final adjustment (attached a weight to the bottom as ballast to reduce rolling if the load wasn't exactly centered) and it was finished.
$5 of juice + 10 minutes = one successful physics boat
Ellen's teacher didn't believe it would work and actually mocked the design. Fool! Bow to the magnificence of it's simplicity. It worked like a charm. A+
