Floating and sinking seems pretty straight forward. Wood floats and rocks sink. Light things float and heavy things sink. Although this is a pretty proven fact, there are some exceptions to that rule that get us to start thinking. Why do somethings float and others sink?
For the tinfoil boat, I started with the picture above. It ended up working really well and I was able to put around 150-160 pennies in it before it sunk to the bottom.
I tried one more boat to see if that would make any difference in the final result. This one was a little smaller with higher walls.This boat was less successful in that it only held around 90 pennies in comparison to the 150ish that the previous boat was able to hold.
I tried to make a flinker out of a styro-foam cup, tape, and then either pennies or marbles. I got close at one point, but never was successful. I tried placing the pennies on top of the cup just to increase the weight a little bit but the cup just kept flipping over. I also tried taping some marbles inside of the cup which is when I was the closest. It would slowly go down and then come back up but only to sit back on the surface.
After doing some exploring and then reading the article on how an ocean liner of steel can float, I found support for the idea that things float when they are less dense then the water as well as when they displace as much water as they weigh. The more surface area the object has, the more water it will displace, causing it to float. The article talked about clay. If the clay is in a ball, it will sink. If it is shaped like a boat, it will float. The density hasn't changed because it is the same amount of clay, but the surface area has grown so it is displacing more water than the ball was which caused it to float.
This made me come to these conclusions:
Rocks can float in water if their density is less than the water or if the rock displaces enough water that the buoyant force is equal to the gravitational force.
Wood can sink if the density of the wood is greater than the density of the water.
Excellent thoughts, Heidi! I also tried making two different boats. One held 35 pennies and the other held 150 pennies. Interestingly, like yours, my boat with a greater surface area was the one that was able to hold more weight before sinking. Since I noticed this, I came to a same conclusion that you did on the sinking wood and floating rock.
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