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Question:
A man, or woman, for that matter, is in a very large, calm pool of water. There is also a large ship, a super tanker, maybe. My question is, Could the person in the pool, with back against the wall and legs against the hull of the ship, push hard enough to actually move the ship? I have a class of 27 students (and mysely) who are as curious as can be to know the answer. P.S. Is Ian Tasker still about??



Replies:
Robert,

Yes. Any force the person applies to ship will accelerate the ship according to Newton's law, F=ma. The acceleration, a, will be given by a=F/m. Since F is relatively small and m, the mass of the ship, is very large, the acceleration will be extremely small. Since you said the pool is calm, I assume the person's legs are the only force acting on the ship, so the ship will accelerate. The distance the ship moves can be calculated from the acceleration and time. Of course, as soon as the ship begins to move, there will be hydro- and aerodynamic drag forces acting to slow the acceleration. In a real world, the water will not be calm, the force exerted by the heaving water will vastly overpower the pitiful force of the person, and the hapless swimmer would likely be squashed like a bug.



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