Wednesday - April 29, 2009

Trying to break Hooke’s Law

Are any of you BMEWSers physics types, or mechanical engineers? I’m trying to understand something about coil springs and levers, and the amount of energy they can impart over time. And it’s been a very long time since Calc III, so I’m hoping your explanation will involve only small amounts of math.

Given a set up like this ...




we have a hammer on a pivot, being propelled by a coil spring riding on a pivoted sliding rod. You pull back the hammer to the release point, which compresses the spring. Release the hammer and it zips down and whacks the little black nail which sticks out of the board.

BUT there is a red stop block in the way, so that the hammer can not go all the way to the board. The spring is never fully relaxed. Even if the hammer was able to hit the board, the spring would still have some compression. When the hammer is pulled back to the release point, the spring is not fully compressed. The spring is very strong, strong enough to move the hammer very quickly.

What I want to know is, if I put that little green spacer between the hammer and the nail, will the hammer impart more force to the nail? The spacer does not contact the red stop block.

Oh, and this is a NASA project, so gravity has no part to play here. Nor does pivot friction, and the spacer is made of unobtanium, that magic material that instantly transfers energy without absorbing any.

Yes, of course this is a “gun thingy” question. I’m trying to figure out if a thicker transfer bar (the green spacer) will cause the hammer to hit the nail (the firing pin) harder and/or sooner. I figure it ought to hit sooner because the spacer shortens the distance the hammer has to travel before it can transfer energy to the nail. And I think it might hit harder - transfer more energy - because the spacer gives it more time to do so - momentum? - before the little red block stops the hammer. But I’ve been told this idea is faulty, and I don’t see why. I’ve been told that making the red block thinner will make the hammer hit harder, but let’s assume that block is made out of some insanely hard material that I can’t carve down. So I came up with the spacer idea, which I think would have the same effect.

When I get an answer I can understand, this device will be used as a cartoon mousetrap.

Posted by Drew458     on 04/29/2009 at 05:36 PM   
Filed Under: • Miscellaneous •  
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