Saturday STEM Challenge: Raft Building
For New Hampshire’s April school vacation week, when none of us is actually going anywhere, we decided to focus on things we could do if we did have some sort of wild vacation adventure and ended up on a deserted island.
We’ve been stuck on this deserted island all week and have been learning lots of survival skills. We learned how to make a compass, how to use the sun to cook food and make drinkable water, how to use our senses to get a better idea of our surroundings, and how to use the stars for navigation. But now, we’ve had enough of island living and we want to get back home. To get off this island, we’ll need to build a raft.
For our raft to be successful, it needs to float, even when there’s a person sitting on it (since we’ll be making mini rafts, we’ll represent the weight of a person with coins). So before we construct our raft, it might be worth asking: how do boats float?
When an object is in water, there are two forces acting on it: the downward force of gravity and the upward force of buoyancy. The force of gravity is dependent on the weight of the object, and the force of buoyancy is dependent on the weight of water that was displaced by the object. An object floats if gravitational force is less than the buoyancy force—that is, if the weight of the object is less than the water it displaces.
So for our raft to float, we need to make sure it displaces as little water as possible. The challenge is figuring out how to do that!
Let’s say that that only thing we got stranded with on this island is 2 feet of string and 6 inches of duct tape. We can use anything that we find on our island to construct our raft (i.e. whatever you can find outside your home: sticks, leaves, etc.). Once you’ve done that, fill up your kitchen sink, your bathtub, or a bucket with some water and test your raft. See how much weight your raft can hold without sinking by placing pennies on it. Good luck!
