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Tony Sandy

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Is there an advantage of spin over percussion, when it comes to moving objects through space?

I've noticed that frisbees*, drills, javelins, propellers (planes, submarines, helicopters), arrows, rifling in gun barrels all cause spin or spin naturally. Is this because forward momentum creates displacement (pressure at the front/ vacuum at the back or in the case of deliberate propulsion as in jet engines, vacuum at the front, forward momentum from the back as the sucked in air expands at the back, pushing the craft forward)?
Also does percussion as in hammer drills and the rocket that was supposed to be propelled by minor nuclear explosions (staccato versus smooth flow), have any advantage over spin (think also of nail versus screw or saw versus axe)?

*discs show lack of resistance all round, by transferring what part of the edge is facing forward as pointed objects keep the narrowest part of themselves in the forward position - likewise spheres spin in the same way as discs, being rotated by friction, I believe.


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  • Feb 29 2012: Actually I don't quite.

    What I was trying to get at, was that there's a common principle at work, to do with displacement (That 'Eureka!' moment). Apart from the objects mentioned, I also see it in windmills and swimming - where forward motion is obtained by scooping what is in front of you, behind. In fact I now realize it's the law of motion, about movement in one direction causing equal movement in the opposite direction.

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