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Lever

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Lever

1. 1. Lever By: Group 2
2. 2. Did you know that pliers, scissors, and the crowbar are examples of a lever? A lever is a simple bar that can rotate about a point called a fulcrum.
3. 3. Do you know that certain parts of human act as levers?
4. 4. Levers are force multipliers as well as distance multipliers. In pliers, a small force handle produces a large force at the jaw. In the human arm, a small movement of a muscle causes a large movement of the hand. Some levers also change the direction of the force applied.
5. 5. A lever is a machine consisting of a beam or rigid rod pivoted at a fixed hinge, or fulcrum. It is one of the six simple machines is identified by Renaissance scientists. The word comes from the French lever, "to raise". A lever amplifies an input force to provide a greater output force, which is said to provide leverage. The ratio of the output force to the input force is the ideal mechanical advantage of the lever.
6. 6. 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:
7. 7. 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.
8. 8. 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.
9. 9. 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.
10. 10. The mechanical advantage for various levers can be calculated by measuring the force applied and the force produced using the equations previously given. The mechanical advantage can also be calculated by measuring the effort arm ( the distance from the fulcrum to the effort, De) and the resistance arm (the distance from the fulcrum to the resistance, Dr). This is the theoretical mechanical advantage.
11. 11. It will be good to remember as well some properties of MA for the different type of levers. First-class levers (fulcrum between the forces) MA can be <1,= 1, or >1. Second-class levers (resistance force between effort force and fulcrum): MA always >1. Third-class levers (effort force between resistance and fulcrum): MA always <1.
12. 12. Look at the system below. A load of 30N is supported by a 10 N effort. What is its mechanical advantage