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Why does a tiny rock sink to the bottom of a lake, while a giant boat can stay afloat?
When any object hits water, it displaces some amount of water. To float, the object needs to be lighter than the amount of water it displaces.
Rocks are dense. They are small, so they don’t displace a lot of water, and they are relatively heavy for their size. This means they will sink.
Boats, meanwhile, are very large, so they displace a lot of water. Boats are also mostly hollow, so they are not very dense for their size. A boat is lighter than the amount of water it displaces, so it floats.
This is a scientific principle called buoyancy. Anything that floats can be called buoyant.
You can test this out yourself with a paper boat. All you need is a piece of letter paper.
Follow the steps below, adapted from Kyrin Crafts on YouTube, or watch the original video:
1. Fold your paper in half horizontally, or hamburger style. Keep the crease at the top.
2. Fold the top corners in so they meet in the middle.
3. Fold in the bottom corners so they meet the edge of your first fold.
4. Keeping the corners you just folded, fold the entire strip at the bottom of your paper up. Flip it over and do the same on the other side.
5. With two hands, grab the middle of your paper. Then pull it open. You should have a square piece of paper, with the middle parts you pulled becoming two corners.
6. Fold the bottom corner up toward the top corner. If you want to be able to see the “mast” of your finished boat, don’t pull the bottom corner all the way to the top.
7. Grab the middle of the bottom of the paper from both sides and pull it open again.
8. Two triangles should be on the sides of your paper. Pull them both open — it’s starting to look like a boat!
9. Look at the bottom of your boat and gently open it, creating empty space.
10. Fill up a sink or tub and set sail.