Homework Help: Does a cube of aluminum yield in the sea?

hermtm2 · Aug 31, 2012

1. The problem statement, all variables and given/known data

A cube of aluminum is suspended deep in the ocean. Will it yield if it is placed deeper and deeper in the ocean?

2. Relevant equations

3. The attempt at a solution

I guess that it will yield since the pressure from water will be stronger as it goes deeper.

Thanks,
Ryan.

CWatters · Aug 31, 2012

No.

This is a solid block of aluminium right? The pressure inside is going to be the same as outside. You might be able to compress the aluminium very very slightly I suppose. However I think the temperature difference down there is likely to have a bigger effect on the volume of the cube than the pressure.

hermtm2 · Aug 31, 2012

So the cold temperature prevents changes in volume?
I did not think about that.

Thanks,
Ryan.

Mark44 · Sep 1, 2012

CWatters said: ↑

No.

This is a solid block of aluminium right? The pressure inside is going to be the same as outside.

Not necessarily. If the pressure exerted by the water is greater than the repulsive force of the aluminum molecules, then the compressive force of the water will cause the aluminum to be compressed to some degree. As the molecules of aluminum get closer together, the repulsive force between them would be increased, until the outer force and inner force reached equilibrium.

That's how it seems to me.There must be tables somewhere of the compressive strength of aluminum - the number of pounds per sq. in. (or newtons per sq. cm.) it takes to deform it. You could also calculate the pressure at various depths, say at the bottom of the Marianas Trench, which is around 30,000 below sea level.

CWatters said: ↑

You might be able to compress the aluminium very very slightly I suppose. However I think the temperature difference down there is likely to have a bigger effect on the volume of the cube than the pressure.

Hard to say. I'm sure there are tables of the water temperature at various depths. I don't believe it's too much below 0° C.

CWatters · Sep 1, 2012

Mark44 said: ↑

Not necessarily. If the pressure exerted by the water is greater than the repulsive force of the aluminum molecules, then the compressive force of the water will cause the aluminum to be compressed to some degree. As the molecules of aluminum get closer together, the repulsive force between them would be increased, until the outer force and inner force reached equilibrium.

That's what I meant. Sorry if not clear.

CWatters · Sep 1, 2012

hermtm2 said: ↑

So the cold temperature prevents changes in volume?

No, what I meant was the block might "shrink" more due to the lower temperature than due to the increased pressure. However I haven't looked for the figures for aluminium.

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Homework Help: Does a cube of aluminum yield in the sea?

hermtm2

CWatters

hermtm2

Mark44

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CWatters

CWatters