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Simple Machines: Pulling with Pulleys

Everyday Einstein explains how simple machines like pulleys can become force multipliers, helping you do twice as much work…but for a price.

By
Lee Falin, PhD,
April 19, 2013
Episode #051

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Simple Machines: Pulling with Pulleys

“Force multiplication” is a term used by the military to refer to a technology or skill that makes a military force more effective. Guided missiles, physically fit troops, combat drones, body armor, and even good spirits are all examples of military force multipliers.

Well, it turns out that you use force multipliers every day, even if you’re not in the military. You see, a special set of force multipliers have been studied by scientists going all the way back to Archimedes. These force multipliers are called simple machines. A simple machine is a basic mechanical device that changes the magnitude or direction of a force. 

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Quite the Advantage

Simple machines are considered force multipliers because they actually let you…multiply your force. Remember that force is equal to mass times acceleration, so a machine that lets you multiply your force will allow you to move heavier loads than you’d normally be able to, or to move them faster than you’d normally be able to. Just how much of a multiplication the machine gives to your force is called the mechanical advantage of the machine.

Wait a second; does this mean you’re getting something for nothing? Am I talking about some magic machine that can do your work for you? Unfortunately, no. Remember back when we were talking about work and we said that work is equal to force times distance? In other words, the amount of work you do is equal to the amount of force you apply to an object, multiplied by the distance the object moves.

A simple machine can’t change the amount of work you do, because work is equivalent to energy, and the law of conservation of energy doesn’t allow for energy to come from nowhere. Instead, a simple machine lets you trade distance for force.

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