What is the condition for a body to sink?
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Archimedes principle is straightforward
Archimedes' principle states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces and acts in the upward direction at the center of mass of the displaced fluid.
But, why is it true? Imagine a body of water that has been left undisturbed for a long time. Eventually all of the inner currents will slow and stop. The water will be perfectly still.
Important: The water is not moving, it is still. there are no net forces on any section of water. The force pushing up is equal to the force pushing down.
Now, imagine the force of compression at any level below the surface. It is made of the weight of the atmosphere and the weight of the water above it. Call this force X. Picture a water molecule at this level, it is not moving. If it is not moving, then all of the forces on it are equal(within the weight of the one water molecule) and the force is caused by the weight of the atmosphere and the weight of the water above it.
So, if we submerge something lighter than water to this level, let’s say a cork. Then we add all the forces compressing the water from above, we come up with a force less than X. Why? because we add the atmosphere the weight of the water above the cork and the weight of the cork itself.
Now, the upward pressure of the water on the bottom of the cork is greater than the weight pushing down on the cork. Release the cork and it moves upwards.
Archimedes' principle states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces and acts in the upward direction at the center of mass of the displaced fluid.
But, why is it true? Imagine a body of water that has been left undisturbed for a long time. Eventually all of the inner currents will slow and stop. The water will be perfectly still.
Important: The water is not moving, it is still. there are no net forces on any section of water. The force pushing up is equal to the force pushing down.
Now, imagine the force of compression at any level below the surface. It is made of the weight of the atmosphere and the weight of the water above it. Call this force X. Picture a water molecule at this level, it is not moving. If it is not moving, then all of the forces on it are equal(within the weight of the one water molecule) and the force is caused by the weight of the atmosphere and the weight of the water above it.
So, if we submerge something lighter than water to this level, let’s say a cork. Then we add all the forces compressing the water from above, we come up with a force less than X. Why? because we add the atmosphere the weight of the water above the cork and the weight of the cork itself.
Now, the upward pressure of the water on the bottom of the cork is greater than the weight pushing down on the cork. Release the cork and it moves upwards.
sweetyverma595:
Thanks for this but I asked something else...
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The condition that is necessary for a body to sink is the weight of the body should be greater than the upthrust force, then it will sink.
hope it helps you
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