How Does a Wrench Work?
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Wrench Head
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A wrench works using the principles of leverage and mechanical advantage. It's a process by which all machines work. The wrench applies direct force to an object, usually a bolt. This force is more direct because the wrench is formed to fit perfectly on the bolt head. If you tried to use your hand to loosen the wrench, you wouldn't get very far. That's because your fingers are soft, and can not grip the bolt head. A wrench has straight sides that lock onto the head of the bolt, gripping without give.
Applying Force
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Once a wrench is securely mounted to a bolt, you need to apply force to the wrench in order to loosen the nut. This force is generally applied by a person pushing or pulling the wrench in an arc in a counterclockwise motion. This motion and force transfers down the wrench to the head of the bolt, causing it to turn and loosen.
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Mechanical Advantage
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A wrench supplies mechanical advantage in two ways: the first is better grip as explained in section one; the second is leverage. This leverage is gained by the length of the wrench arm. You may have noticed that when you hold you hands at the end of the wrench arm it is much easier to turn a bolt, but if you choke up on your grip near the head of the wrench, that same bolt won't budge. That's because the farther away you get from the bolt, the more mechanical advantage you have. The end of the wrench arm is actually moving farther (in a larger arc) than the head of the wrench, so more power is being applied to the center, which is moving in a smaller arc.
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