# The Naked Scientists Forum

### Author Topic: When I have a bath...?  (Read 4509 times)

#### Seany

• Neilep Level Member
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##### When I have a bath...?
« on: 14/12/2007 23:20:43 »
When I have a bath.. Is it the density or volume of my body that makes the water level rise?

If I get a bowling ball with a really heavy density and a bowling ball with a lower density, when the more dense one is placed in a bath, does the water level rise more?

OR was I correct in thinking that it is the volume, and not the density?

#### another_someone

• Guest
##### When I have a bath...?
« Reply #1 on: 15/12/2007 02:03:29 »
It is both.

Density determines whether the thing will float or sink, and to what portion it will sink; but insofar as it does sink, it will be the volume of the object that is beneath the water that will determine how much the water will rise.

BTW, welcome back Seany.

#### lyner

• Guest
##### When I have a bath...?
« Reply #2 on: 15/12/2007 22:15:41 »
Archimedes sorted this out a long time ago. You displace water when you get into it. The upthrust which you experience is equal to the weight of the water you have displaced. If you are less dense than water, you will sink deeper until the weight you displace equals your own weight - you will float. If you are more dense, even when you are under the water, the weight of displaced water is not enough to overcome your weight; you will sink. It's all a matter of density relative to the fluid in which you are immersed.

#### another_someone

• Guest
##### When I have a bath...?
« Reply #3 on: 16/12/2007 07:39:46 »
Archimedes sorted this out a long time ago. You displace water when you get into it. The upthrust which you experience is equal to the weight of the water you have displaced. If you are less dense than water, you will sink deeper until the weight you displace equals your own weight - you will float. If you are more dense, even when you are under the water, the weight of displaced water is not enough to overcome your weight; you will sink. It's all a matter of density relative to the fluid in which you are immersed.

But the point I was making is that it is all a matter of density relative to the fluid, until to exceed the density of the fluid.  When that point is reached, then any further increase in mass (and thus is density) will not cause any increase in displacement, since you have already sunken to the bottom whatever increase in mass you have.  At that point, the only variable that matters is volume (until a further increase in volume causes a sufficient decrease in density as to cause partial floatation).

#### lightarrow

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##### When I have a bath...?
« Reply #4 on: 16/12/2007 18:22:48 »
But the point I was making is that it is all a matter of density relative to the fluid, until to exceed the density of the fluid.  When that point is reached, then any further increase in mass (and thus is density) will not cause any increase in displacement, since you have already sunken to the bottom whatever increase in mass you have.  At that point, the only variable that matters is volume (until a further increase in volume causes a sufficient decrease in density as to cause partial floatation).
That's correct.

#### The Naked Scientists Forum

##### When I have a bath...?
« Reply #4 on: 16/12/2007 18:22:48 »