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Q & A: Simple machines

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Most recent answer: 02/22/2015
Q:
I'm struggling to understand the reasoning behind categorizing an inclined plane as a simple machine. Pulley, lever, wheel&axel, Wedge Screw Inclined plane... I get the first five - and I understand that a it's easier to go up a ramp (inclined plane) than a wall - But ...the ramp doesn't DO anything.Levers lift, pulleys pull, wheels/gears turn axels, wedges separate, screws push aside...ramps sit there. The best answer I've had so far is that all these things make it easier to lift things (in which case, why not include a balloon?)...But I thought the definition had to do with ACTING on a force and I don't understand how a ramp acts on anything.Thanks in advance.
- Karen (age 40)
Westminster, CO 80031
A:

From your perspective, none of the machines actually 'do anything' and in fact that is indeed somewhat true. All the simple machines are simply bound by the laws of physics, including energy conservation. δE = F.δx, that is neither force nor the distance that this force acts on the object needs to be separately conserved during the process: however the integral should be. Simple machines ideally do not convert any energy into mechanical energy or vice versa, as opposed to a train engine which converts the chemical energy of diesel into mechanical energy. An inclined plane simply reduces the force needed to be applied, but the distance that you push something to elevate it to the same height also increases with the same factor, so that the energy to be supplied is the same. Similarly for pullleys, you need to pull the rope twice, thrice ...

Of course, this was assuming that there is no friction. You will be at a slight disadvantage in real inclined planes due to frictal heat dissipation. And here is where the wheels come into play: because they can rotate, wheel and floor surfaces are 'motionless' with respect to each other at the contact point. This means δx=0, so no energy loss due to friction.

Tunc

 


(published on 02/22/2015)

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