Test your buoyancy understanding!

[xozzx]

Hey, just a bit of fun, test your understanding of buoyancy / diving related physics.

2 (easyish) questions for now...

- You have a canoe in a swimming pool with a rock inside the canoe. You throw the rock out of the canoe into the water. What happens to the level of the swimming pool?

- You have a canoe with a rock hanging off the front on a rope, completely submerged with water. If you cut the rope what happens to the level of the swimming pool?

Also explain your answer!

 

[SnorkelLA]

1. The level stays the same. Even if the rock was in or out of the canoe it doesn't change the fact that there's a rock and a canoe in the pool. Therefore the level will stay the same

2. Stays the same. Same reason as the first question

 

[Tigerman]

What happens is that you break the tiles on the bottomn of the pool, which makes the maintenance people VERY pissed off..

 

[xozzx]

1. The level stays the same. Even if the rock was in or out of the canoe it doesn't change the fact that there's a rock and a canoe in the pool. Therefore the level will stay the same

2. Stays the same. Same reason as the first question

Nope! Tho that is what most people would answer.

 

[The Chairman]

English or African rock?

 

[TMHeimer]

Nope! Tho that is what most people would answer.

That would've been my first guess. Does it have to do with the rock at first either being out of the water (in the canoe) or tied to the canoe which is not completely submerged--thus the end result being the water level rising? Displacement obviously has something to do with it, no? NO-- wait wait... When the rock is in or attached to the canoe the canoe plus rock is considerably heavier and thus displaces more water over a wide area than when the rock is on the bottom, so the water level goes down. The rock's water displacement is very small compared to the conoe's. How's that?

 

[sdeachoe]

Thank you, LOL!!! :laughing:

 

[diversteve]

In both instances the water level decreases slightly. The first because you're reducing the displacement of the canoe hull when you throw the rock overboard.

The 2nd is similar but the water level should decrease less because the weight of the rock in water will be slightly less as it's more buoyant (yes rocks are buoyant - just not very) so it is pulling the canoe hull down slightly less. It's less of a net change because the rock is already displacing it's volume in the water.

You have a canoe with a rock hanging off the front on a rope, completely submerged with water.

However, the way you wrote this - if the canoe itself is completely submerged in the water - the net change is zero...lol

 

[Insta-Gator]

What type of rock and it's related specific gravity?

 

[TMHeimer]

The rock's water displacement is accounted for no matter where is is, but the canoe's displacement decreases with no rock in it or attatched to it. So the water level decreases.