Selina Solutions Class 9 Physics Solutions for Exercise 5A in Chapter 5 - Chapter 5 Upthrust In Fluids Archimedes Principle And Floatation

Question 1 Exercise 5A

What do you understand by the term upthrust of a fluid? Describe an experiment to show its existence.


Upthrust is an upward force that acts on a body when it is partially or fully immersed in a fluid.

Following is an experiment that demonstrates the existence of upthrust:

When an empty can, with its mouth sealed with an airtight stopper, is placed in a tub filled with water, it floats with a significantly larger portion of it above the water surface while only a small portion of it is present below the water surface.

If we try to push the can we feel an upward force opposing the push making it difficult to push further? In order to push it further, more force is required until it is fully immersed. Even when it is

fully immersed, a constant force is still required in order for it to remain static in the same position.

That is the maximum thrust on the can. At this position, if the can is released, it bounces back to the water surface and floats again.

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