Originally Posted By: paul

now suppose we move the earth and put the pipe there , the pipe would feel the same 4000N force?

Of course.

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if so then how could the mass moving through the turn apply a 8000N force to the pipe?

Because the turning mass isn't just stopping, it's turning around. It's a whole different situation.

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have you ever considered that the 4000N force is distributed evenly to the turn?

Of course, that's been a fundamental assumption throughout. Sure it doesn't have to, but why complicate things with varying forces.