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we all know about the experiment of the spinning bucket full of water. The water does not fall if the speed of the bucket is right (at least equal to the critical speed or larger than it).

If there was no bucket the water would not fall on our heads either if the water moved at the critical speed. But the water would move in a parabolic path. The higher the speed the larger the parabolic path would be an the farther it would fall. Like when a water jet comes out of a water hose and we don't get wet....

What the bucket does is to keep the water trajectory in a circular path of fixed radius: once the water made it beyond the highest point of its trajectory it would continue to move parabolically.The bottom of the bucket prevents the water from doing that and keeps it in the circular path...

The water does not fall on our heads because it is moving tangentially to the circular path faster than it is moving downward due to gravity. Gravity pulls it down but at a rate that is matching the tangential speed.

So the force of gravity, allowing the water to move in a circle is the main component of the actual centripetal force. If the speed is larger than the critical speed the contact force of the bottom of the bucket, pointing towards the center, helps the water stay in the circular path. Otherwise the water would climb up to follow its natural parabolic path....

So these two force, gravity and the contact force are what produce the circular path, hence they are together the net centripetal force....

Any flaw with my explanation?

thanks

fisico30

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# Water in a spinning bucket: a better explanation

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