A piece of wood if left under water, comes to the
surface. Explain the reason.
Describe an experiment to show that a body immersed in
a liquid appears lighter than it really is.
Will a body weigh more in air or in vacuum when weighed
with a spring balance ? Give a reason for your answer.
Answers
Explanation:
When a body is partially or wholly immersed in a liquid, an upward force acts on it. This upward force is known as an upthrust.
Upthrust can be demonstrated by the following experiment:
Take an empty can and close its mouth with an airtight stopper. Put it in a tub filled with water. It floats with a large part of it above the surface of water and only a small part of it below the surface of water. Push the can into the water. You can feel an upward force and you find it difficult to push the can further into water. It is noticed that as the can is pushed more and more into the water, more and more force is needed to push the can further into water, until it is completely immersed. When the can is fully inside the water, a definite force is still needed to keep it at rest in that position. Again, if the can is released in this position, it is noticed that the can bounces back to the surface and starts floating again.