Simple problem?
In which direction will it rotate if they are equivalent distence from the center? (standard conditions!!!) In this picture: left-1kg iron, right- a 1kg feather pillow
Inspired by
Molnár Krisztián
. The video about this problem isn't in English. He was able to solve this problem, but he didn't prove that.
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2 solutions
As feathers have less density than that of iron, a kilo of feathers will definitely have more surface area than that of a kilo of iron
As pressure is higher on obiects with either greater force (which is what weight is) or less surface area, the balance will tend to turn on the direction of the iron, which is counter-clockwise
Formula of Pressure
area force
F = ρ a i r g V b o d y
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Can someone explain, why they are moving in the first place and how is pressure here?
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The orange force is the buoyancy
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I think it acts in liquids?
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@Vinayak Srivastava – Not only...
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@A Former Brilliant Member – I think it won't move.
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@Vinayak Srivastava – Buoyancy is caused by the pressure difference. We can observe pressure difference in the air too.
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@A Former Brilliant Member – OK, but iron and feather are solids.
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@Vinayak Srivastava – And what is the problem with this?
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@A Former Brilliant Member – They are both of same weight, so it won't move.
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@Vinayak Srivastava – F = ρ a i r g V b o d y and ρ i r o n > ρ f e a t h e r . Thus V f e a t h e r > V i r o n and F f e a t h e r > F i r o n
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@A Former Brilliant Member – P.S. We can't interpret the ρ f e a t h e r .
@A Former Brilliant Member – Buoyancy is not caused by the pressure difference. It is due to the force exerted by a fluid (liquid, vapour, gas, liquid crystal) on a body submerged in it which is displaced by the body
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@A Former Brilliant Member – And where is the plasma? :) I learned that : p t o p − p b o t t o m = p , where p > 0 . F = p ∗ A
@Hamza Anushath, i think your answer goes in wrong direction...its not all about surface area instead of it density is the keyfactor. Let us do a thought experiment consider i have two sheets of gold of same volume in which one have a large surface area and another have smaller surface area.Now,which sheet should feel greater buoyant force in a fluid.According to you,it should be larger one but,that will not happen buoyant force will be vdg and in both the cases v is same although one have greater surface area(I have neglected the quantum things and only try to light up macroscopic one)...
Hey Hamza, the bouyancy force does not depend on surface area but only on the volume.
What we call weight is the net force imbalance acting on a body due to gravity and buoyancy of air. The buoyancy of air is the weight of air displaced by the body, provided there is air surrounding the body. In vacuum, the arm of the balance will not be tilted at all. It will remain horizontal. In presence of air, buoyancy will depend on the volume of air displaced by the body. The force of gravity is the same for both the iron and the feather pillow. Since the volume of the pillow is much greater than that of the iron, buoyancy on the pillow will be much more, and the net downward force acting on it will be much less. Since a common balance compare the weights of the two bodies, and since the net downward force is more on the iron, the arm on the iron's side will go down, resulting in a Counterclockwise rotation .