1. labor-saving lever:

Labor-saving lever, the lever with power arm larger than resistance arm, has the advantage of labor saving, but the disadvantage is that it needs a long distance. For example: nut clips, doors, staplers, diving boards, wrenches, bottle openers (for beer) and trolleys (for transporting cement and bricks). Examples: tweezers, arms, fishing rods, paddles, jaws of kayaks, shovels, brooms, clubs, hair clippers and other appliances with one hand as the fulcrum and the other hand as the power.

2. Equal arm lever:

Power arm is equal to the lever of resistance arm. Example: seesaw, balance, etc.

3. laborious lever:

The power arm is smaller than the lever of the resistance arm, which has the advantage of saving distance and the disadvantage of being laborious. Examples: tweezers, arms, fishing rods, paddles, jaws of kayaks, shovels, brooms, clubs, hair clippers and other appliances with one hand as the fulcrum and the other hand as the power. But all levers are not labor-saving, so there is no machine with mechanical efficiency greater than 1.

Application of lever:

1. Cut hard objects. It takes a lot of force to cut hard objects, which shows that there is a lot of resistance. Use scissors with longer power arm and shorter resistance arm.

3. Paper-cutting or cloth can cut soft objects such as paper or cloth with less force, indicating that the resistance is small, and at the same time, in order to speed up the cutting speed, the knife edge should be longer. Scissors with short arm and long arm.

3. When cutting branches, on the one hand, the branches are hard, and the power arm of scissors is required to be long and the resistance arm is short; On the other hand, in order to speed up the trimming and trim neatly, the cutting edge is required to be longer. Use scissors with longer power arm, shorter resistance arm and longer blade.

Reference to the above content: Baidu Encyclopedia-Lever