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Physics "Quiz" Question 11:25 - Apr 5 with 3568 viewsBOjK

You are in a small rowboat in a large swimming pool (don't ask).

In the boat is a large rock. You throw the rock overboard and it sinks to the bottom of the pool.

What happens to the level of the water at the side of the swimming pool?

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Physics "Quiz" Question on 11:26 - Apr 5 with 1859 viewshype313

Presume it falls?

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Physics "Quiz" Question on 11:29 - Apr 5 with 1846 viewsclive_baker

There would be a ripple effect presumably from dropping the rock, so in that respect it would go up and down. But the non pedantic answer I suspect is 'nothing'.

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Physics "Quiz" Question on 11:30 - Apr 5 with 1838 viewsDarth_Koont

Goes down, I'd say.

The rock is heavier than water so it can displace more water in a larger boat than in the pool where it only displaces its own volume.

But I've probably thought about that wrong.

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Physics "Quiz" Question on 11:31 - Apr 5 with 1834 viewsGeoffSentence

http://www.twtd.co.uk/forum/384784/things-that-float-weigh-as-much-when-floating

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Physics "Quiz" Question on 11:31 - Apr 5 with 1827 viewsclive_baker

Physics "Quiz" Question on 11:30 - Apr 5 by Darth_Koont

Goes down, I'd say.

The rock is heavier than water so it can displace more water in a larger boat than in the pool where it only displaces its own volume.

But I've probably thought about that wrong.


on reflection I would go with this too.

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Physics on 11:32 - Apr 5 with 1815 viewslowhouseblue

edit - it depends on the relative density of the rock and the boat.
[Post edited 5 Apr 2017 11:33]

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Physics "Quiz" Question on 11:33 - Apr 5 with 1810 viewsMJallday

it goes up.

when the rock was in the boat being held by the person, the water level was only being affected by the displacement mass of the bottom of the boat , not the content of the boat

so when you drop something in the water, the water level will go up, because the water will be displaced by the mass of the rock. that mass is not directly linked to the displacement mass of the boat.

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Physics "Quiz" Question on 11:43 - Apr 5 with 1777 viewsITFC_Forever

Physics "Quiz" Question on 11:33 - Apr 5 by MJallday

it goes up.

when the rock was in the boat being held by the person, the water level was only being affected by the displacement mass of the bottom of the boat , not the content of the boat

so when you drop something in the water, the water level will go up, because the water will be displaced by the mass of the rock. that mass is not directly linked to the displacement mass of the boat.


So why do boats sit lower in the water when fully loaded and higher when empty if the displacement is only due to the bottom of the boat and not the boat's content?

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Physics on 11:47 - Apr 5 with 1766 viewsGuthrum

After the initial ripples from the splash, there will be a slight reduction, assuming the density of the rock is greater than that of water (which it must be, in order to have sunk). This being due to the boat no longer having to displace a mass of water equal to the mass of the rock in order to maintain bouyancy. The difference in displaced volume will be greater than the volume of the rock.

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[Post edited 5 Apr 2017 11:50]

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Physics "Quiz" Question on 11:47 - Apr 5 with 1751 viewsSteve_M

The loser's ribbons?

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Physics "Quiz" Question on 11:47 - Apr 5 with 1750 viewsDolly2.0

Physics "Quiz" Question on 11:29 - Apr 5 by clive_baker

There would be a ripple effect presumably from dropping the rock, so in that respect it would go up and down. But the non pedantic answer I suspect is 'nothing'.


Yep, this was my first thought.

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Physics "Quiz" Question on 12:00 - Apr 5 with 1717 viewsclive_baker

Physics "Quiz" Question on 11:47 - Apr 5 by Dolly2.0

Yep, this was my first thought.


Wrong though I reckon.

If the rock was taken out completely, taken out and left on the side of the pool, the water level would go down.

Then when dropped in, it would go up. Question is does it go back up as much as it goes down when it's out of the boat. Given it weighs more than water (hence sinking) I would say no. In the water it's only displacing the size / volume of water it's replacing. In the boat it's replacing it's weight (which is more).

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Physics "Quiz" Question on 12:04 - Apr 5 with 1700 viewsDolly2.0

Physics "Quiz" Question on 12:00 - Apr 5 by clive_baker

Wrong though I reckon.

If the rock was taken out completely, taken out and left on the side of the pool, the water level would go down.

Then when dropped in, it would go up. Question is does it go back up as much as it goes down when it's out of the boat. Given it weighs more than water (hence sinking) I would say no. In the water it's only displacing the size / volume of water it's replacing. In the boat it's replacing it's weight (which is more).


I think the answer is that my head now hurts.

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Physics "Quiz" Question on 12:08 - Apr 5 with 1680 viewsGeoffSentence

Physics "Quiz" Question on 12:00 - Apr 5 by clive_baker

Wrong though I reckon.

If the rock was taken out completely, taken out and left on the side of the pool, the water level would go down.

Then when dropped in, it would go up. Question is does it go back up as much as it goes down when it's out of the boat. Given it weighs more than water (hence sinking) I would say no. In the water it's only displacing the size / volume of water it's replacing. In the boat it's replacing it's weight (which is more).


It will go down surely.

When in the boat it will displace the same amount of water as its weight, as the rock weighs more than water it will displace a greater volume of water than when it is submerged, which only be the volume of the rock. So when it is chucked over the side the water level in the pool will drop.

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Physics "Quiz" Question on 12:12 - Apr 5 with 1665 viewswkj

I can safely say the water level would be wet... yeah I failed my A levels physics

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Physics "Quiz" Question on 12:13 - Apr 5 with 1665 viewsReuser_is_God

All depends on how deep into the water the rock caused the boat to float.

The boat would be higher in the water without the rock & the rock alone will cause the water level to rise but this rise in water level could just come from the boat being higher.

All depends on the size & said boat & said rock.

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Physics on 12:15 - Apr 5 with 1651 viewsReuser_is_God

Physics on 11:47 - Apr 5 by Guthrum

After the initial ripples from the splash, there will be a slight reduction, assuming the density of the rock is greater than that of water (which it must be, in order to have sunk). This being due to the boat no longer having to displace a mass of water equal to the mass of the rock in order to maintain bouyancy. The difference in displaced volume will be greater than the volume of the rock.

Bouyancy = a bloke who lives on the Norfolk coast.
[Post edited 5 Apr 2017 11:50]


Basically what I was trying to say.

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Physics on 12:20 - Apr 5 with 1643 viewsGuthrum

Physics on 12:15 - Apr 5 by Reuser_is_God

Basically what I was trying to say.

You're far too intelligent to be a painter buh.


I do have an A Level in Physics (tho not a very good one).

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Physics on 12:21 - Apr 5 with 1635 viewsReuser_is_God

Physics on 12:20 - Apr 5 by Guthrum

I do have an A Level in Physics (tho not a very good one).


I'd say any A level in Physics is a good one!

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Physics on 12:26 - Apr 5 with 1624 viewsNewcyBlue

Physics on 11:47 - Apr 5 by Guthrum

After the initial ripples from the splash, there will be a slight reduction, assuming the density of the rock is greater than that of water (which it must be, in order to have sunk). This being due to the boat no longer having to displace a mass of water equal to the mass of the rock in order to maintain bouyancy. The difference in displaced volume will be greater than the volume of the rock.

Bouyancy = a bloke who lives on the Norfolk coast.
[Post edited 5 Apr 2017 11:50]


Basically block co-efficient, the waterplane area, displacement of the vessel which will include lightship and deadweight.

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Physics on 12:28 - Apr 5 with 1603 viewsMJallday

Physics on 12:26 - Apr 5 by NewcyBlue

Basically block co-efficient, the waterplane area, displacement of the vessel which will include lightship and deadweight.


newcy - just the man

can you lob a container off the side, and see if the ocean goes up?

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Physics on 12:30 - Apr 5 with 1591 viewsGeoffSentence

Physics on 12:28 - Apr 5 by MJallday

newcy - just the man

can you lob a container off the side, and see if the ocean goes up?


I think we have it, it is the number of cargo ships sailing the oceans, not climate change, that is causing sea levels to rise. Anyone know Trump's thoughts on this?

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Physics on 12:36 - Apr 5 with 1570 viewsNewcyBlue

Physics on 12:28 - Apr 5 by MJallday

newcy - just the man

can you lob a container off the side, and see if the ocean goes up?


Sure. Can you employ me after I get sacked please? I will expect the same terms and conditions.

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Physics "Quiz" Question on 13:01 - Apr 5 with 1526 viewsclive_baker

Physics "Quiz" Question on 12:08 - Apr 5 by GeoffSentence

It will go down surely.

When in the boat it will displace the same amount of water as its weight, as the rock weighs more than water it will displace a greater volume of water than when it is submerged, which only be the volume of the rock. So when it is chucked over the side the water level in the pool will drop.


Aren't we saying the same thing?

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Physics on 13:04 - Apr 5 with 1513 viewsBOjK

Physics on 11:47 - Apr 5 by Guthrum

After the initial ripples from the splash, there will be a slight reduction, assuming the density of the rock is greater than that of water (which it must be, in order to have sunk). This being due to the boat no longer having to displace a mass of water equal to the mass of the rock in order to maintain bouyancy. The difference in displaced volume will be greater than the volume of the rock.

Bouyancy = a bloke who lives on the Norfolk coast.
[Post edited 5 Apr 2017 11:50]


Correct.

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