- #1
Tlaloc86
- 2
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I was recently tutoring a first year student, and a question of her assignment was as follows:
Suppose that that you have a bucket of water over a scale. If you then partially submerge an iron rod in the water, while holding the rod so that it does not touches the bucket, will the reading on the scale change? The answer is that yes, the reading n the scale will increase. One possible explanation of this is that the water exerts a buoyant up force over the rod, and therefore the rod will exert a force down over the water, and this force will be registered in the scale.
I was then thinking what would happen in the same scenario, but this time the bucket is empty. After all, air is also a fluid, so it also exert a buoyant force on the rod. Will this also register on the scale? Of course if it does the increase will much smaller than in the previous case since air has much less density than water, but I'm curious if the effect will be there at all. The reason I think there may not be any increase here is that in the previous case we had two phases: water and air, whereas in this case we only have one phase: air, so the two scenarios are not completely analogous. Or maybe the water is "resting" over the bucket, while the air is not...
Anyway, just a rather silly question I cannot wrap my head around :) Thanks!
Suppose that that you have a bucket of water over a scale. If you then partially submerge an iron rod in the water, while holding the rod so that it does not touches the bucket, will the reading on the scale change? The answer is that yes, the reading n the scale will increase. One possible explanation of this is that the water exerts a buoyant up force over the rod, and therefore the rod will exert a force down over the water, and this force will be registered in the scale.
I was then thinking what would happen in the same scenario, but this time the bucket is empty. After all, air is also a fluid, so it also exert a buoyant force on the rod. Will this also register on the scale? Of course if it does the increase will much smaller than in the previous case since air has much less density than water, but I'm curious if the effect will be there at all. The reason I think there may not be any increase here is that in the previous case we had two phases: water and air, whereas in this case we only have one phase: air, so the two scenarios are not completely analogous. Or maybe the water is "resting" over the bucket, while the air is not...
Anyway, just a rather silly question I cannot wrap my head around :) Thanks!