First classification
The first type of leverage: the power F and the useful resistance W are on either side of the fulcrum. Such leverage
Not laborious and effortless. For example, scissors for cutting metal sheets have a very short edge and its mechanical advantage is much greater than one. This is because the metal plate is very hard, the knife edge is short, and the knife handle is long, that is, the power arm is larger than the resistance arm, and less force can be used. The levers that fall into this situation are also the nippers and the like. The scissors for household cutting cloth are basically the same length as the blade, that is, the power arm is equal to the resistance arm, which is a type that is not labor-saving and effortless. Because the thickness of the cloth is thin, it does not require too much force. The cloth should be straight and the knife edge should be longer. For this reason, the force is not large, and the cloth is cut straight. Also of this type are physical balances. Another example is the scissors for haircuts. The knife edge is very long, that is, the power arm is smaller than the resistance arm, and its mechanical advantage is less than one. This is because the haircut does not need much force, the knife edge is longer, and it can be cut faster and better.
The second type of leverage: the fulcrum and the power point are on either side of the useful resistance point. The power arm of this type of lever is larger than the resistance arm, and its mechanical advantage is always greater than 1, so it is always labor-saving. For example, using a sickle to scribble, a wheelbarrow, etc. are all such levers.
The third type of lever: the fulcrum and the useful resistance point are on the two sides of the power point. The power arm of this type of lever is smaller than the resistance arm, and its mechanical advantage is always less than 1, so it is always laborious. For example, the pedals of the sewing machine and the bamboo clips that sandwich the food belong to this type of lever.
Second classification
The first type of lever: it is a labor-saving lever, that is, the power arm is larger than the resistance arm. For example, claw hammers, woodworking pliers, wheelbarrows, soda boards, sickles, etc.
The second type of lever: it is a laborious lever, that is, the power arm is smaller than the resistance arm. Such as scorpions, fishing rods, scissors for haircuts.
The third type of leverage: a lever that is effortless and effortless, that is, the power arm is equal to the resistance arm. Its mechanical interest is equal to one. Such as å¤ flat, fixed pulley and so on.
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