The fulcrum of the lever must be on the lever, because the lever is a contact force, so the center of gravity is not necessarily on the object. Gravity is a field force that can be left untouched, such as the center of gravity of a circle or balloon. A fixed point on which a lever acts to support an object. Fulcrum O: the fixed point around which the lever rotates.
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Lever is also called laborious lever, labor-saving lever and equal arm lever. The lever principle is also called "lever balance condition". To balance the lever, the two moments (the product of force and arm) acting on the lever must be equal. Namely: power × power arm=resistance × resistance arm, expressed as F1 · L1=F2 · L2. Where, F1 represents power, L1 represents power arm, F2 represents resistance, and L2 represents resistance arm. It can be seen from the above formula that to balance the lever, the power arm is several times the resistance arm, and the resistance is several times the power. From On the Balance of Plane Figures.
Lever balance means that the lever is at rest or rotates at a constant speed under the action of power and resistance.
There are two cases of lever force:
1. There are only two forces on the lever:
Power × distance from fulcrum to dynamic action line=resistance × distance from fulcrum to resistance action line
Namely, power × power arm=resistance × resistance arm
Namely, F1 × L1=F2 × L2
2. There are multiple forces on the lever:
The product of the force that makes the lever rotate clockwise and its corresponding arm is equal to the product of the force that makes the lever rotate counterclockwise and its corresponding arm.
This is also called the principle of the lever, which also applies to the case of only two forces.