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I am learning about various types of simple machines like levers, pulleys, ramps at the moment. And in researching about them I see that in all of them even though the work performed stays the same, the way they offer an advantage in performing work ( meaning reducing force applied) is that either distance of work performed increases or the direction of force changes. This makes sense when I think of it mathematically in terms of the w= force * distance equation. But I feel like I am still not satisfied with this explanation and wanted to get a more conceptual explanation of how exactly these machines reduce the force/effort applied.

Like how does increase the distance of lever, ramp or rope pulled exactly reduce force? When the force I (as a human being) apply is reduced is something else like gravity or the rope or the fulcrum or the material of the lever compensating for the amount of force I didn’t have to apply? What is happening at the molecular level that if I push a load up a ramp more distance I don’t have to exert as much force as I would have to if I directly lift the load with my hands without the ramp? If anyone can add anything to this question, I would greatly appreciate it? Thanks.

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To keep some object at rest if some force is exerted on it (like the gravitational force), force of the opposite direction and the same size needs to be produced. If you do not supply all the force needed, the machine itself takes care of the rest.

Take for example lever. You can view the lever + object you wish to raise as being one rigid body. Then the overall force on this lever+object body at rest needs to be zero, otherwise the center of mass would had to accelerate. The lever in its rest state is supported by fulcrum and the ground (at the end that touches it). Both of these produce forces and the torque that compensates gravitational force, so that lever can stay at rest.

Now, once you start to rotate the lever around fulcrum, the fulcrum still supports the lever and produces the forces needed to make the movement just what you observe in practice.

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  • $\begingroup$ Hi. Thank you for the response. I was wondering about the last paragraph where you mention the fulcrum producing the force needed to make the movement. How does the fulcrum produce the force? Is it the opposing force aka the normal force (as dictated by Newton's third law) exerted by the fulcrum since you are pressing on top of it when trying to push down the lever? $\endgroup$ – TLo Oct 14 '20 at 16:45
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    $\begingroup$ @TLo Yes it is opposing force. It is similar to how ground exerts upward force. If it would not, you would fall under it. On molecular level, this is done through electromagnetical forces between molecules, but on macroscopic level you do not care about such details. The ground has simple property of forbidding anything to fall under it and thus the force it exerts is whatever it needs to be to achieve that. Similarly fulcrum keeps the point of contact with the lever at rest and produces forces through intermolecular interactions to achieve that $\endgroup$ – Umaxo Oct 15 '20 at 3:08
  • $\begingroup$ Ahhh... Okay. Thanks so much for clearing my doubts. $\endgroup$ – TLo Oct 16 '20 at 20:48

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