Frostbite Theater

Here's a Question! - A Boat on Water

A boat is placed in a partly filled aquarium. What happens to the level of the water?

Announcer: Frostbite Theater presents... Cold Cuts! No baloney!

Joanna and Steve: Just science!

Joanna: Hi! I'm Joanna!

Steve: And I'm Steve!

Joanna: Here's a question for you...

Steve: An aquarium is partly filled with water and the water level is marked.

Joanna: A boat of dubious construction is placed on the water.

Steve: What happens to the level of the water?

Joanna: Does the level rise?

Steve: Does the level fall?

Joanna: Does the level stay the same?

Steve: Or, does it depend on whether the boat sinks or floats?

Joanna: Pause the video now if you'd like to think it over before we show you what happens.

What happens to the level of the water when the boat is added?

The level rises.

Adding the boat is just like pouring more water into the aquarium.

It takes up space and the only direction that is available is up, so the level of the water rises.

Steve: Now, the amount that the water rises depends on whether the boat sinks or floats.

If the boat sinks, then the boat displaces a volume of water that's equal to the volume of the boat, where 'the volume of the boat' is the volume of all of the pieces of the boat that the water can't flow into.

If the boat floats, then the boat displaces a volume of water with a weight equal to the weight of the boat.

But, in either case, sink or float, the level rises.

Joanna: Thanks for watching. I hope you'll join us again soon for another question!