Classes of Levers
Levers are classified by the relative positions of the fulcrum and the input and output forces. It is common to call the input force the effort and the output force the load or the resistance. This allows the identification of three classes of levers by the relative locations of the fulcrum, the resistance and the effort:
- Class 1: Fulcrum in the middle: the effort is applied on one side of the fulcrum and the resistance on the other side, for example, a crowbar or a pair of scissors.
- Class 2: Resistance in the middle: the effort is applied on one side of the resistance and the fulcrum is located on the other side, for example, a wheelbarrow or a nutcracker or a bottle opener.
- Class 3: Effort in the middle: the resistance is on one side of the effort and the fulcrum is located on the other side, for example, a pair of tweezers or the human mandible.
These cases are described by the mnemonic "fre 123" where the fulcrum is in the middle for the 1st class lever, the resistance is in the middle for the 2nd class lever, and the effort is in the middle for the 3rd class lever.
Read more about this topic: Lever
Famous quotes containing the words classes of, classes and/or levers:
“There were three classes of inhabitants who either frequent or inhabit the country which we had now entered: first, the loggers, who, for a part of the year, the winter and spring, are far the most numerous, but in the summer, except for a few explorers for timber, completely desert it; second, the few settlers I have named, the only permanent inhabitants, who live on the verge of it, and help raise supplies for the former; third, the hunters, mostly Indians, who range over it in their season.”
—Henry David Thoreau (1817–1862)
“We deny your internationalism, because it is a luxury which only the upper classes can afford; the working people are hopelessly bound to their native shores.”
—Benito Mussolini (1883–1945)
“There are two levers for moving men—interest and fear.”
—Napoleon Bonaparte (1769–1821)