Levers consist of an inflexible pole (bar) that pivots on a fulcrum. Levers come in three classes---first, second and third class---each requiring an effort force, a resistance force and a fulcrum positioned somewhere along the bar. For the lever to work correctly, the resistance and effort forces must be balanced. Where first, second and third class levers differ is the location of the fulcrum and the applied force with respect to the load. Consequently, they all act in a different manner and are employed for specialised tasks.
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Hammers act as a first-class lever, with the fulcrum between the effort and the load. When hammering a nail into wood, the arm is the lever, the hammer is the pivot and the load is the nail resisting being driven into a piece of wood at the other end. Reversing the hammer makes the claw end become the fulcrum, trying to remove the nail as it resists being pulled from the wood.
Scissors contains two first-class leavers with the fulcrum (pivot) in the middle. The load is the piece of paper or fabric being cut by the scissors.
Shovels operate as first-class levers. The pole is the lever, the load (resistance) is the rock being lifted from the ground, while the ground under the rock, which anchors the shovel for lifting the rock, becomes the fulcrum.
Wheel barrows perform as second-class levers, which move the fulcrum to the far end of the pole. The handles are the lever, the dirt container holds the load and the wheel is the fulcrum.
Bottle openers, also second-class levers, make a fulcrum out of the bottle cap end. The hand places effort force on the far end of the lever.
Staplers have two leavers---the lever containing the staples and the lever that bends the staple ends as they are being ejected from the other lever. The spring-loaded joint becomes the fulcrum, and paper acts as the load for the staple end.
Nut crackers consist of two second-class levers joined by a pivoting fulcrum at one end. The hands apply effort force to crush the nut between the two levers.
Fishing poles, like other third-class levers, have the fulcrum at one end and the load at the other end. The force is applied in the middle. The reel becomes the fulcrum, and the fish becomes the load, while the pole and line become the lever.
Tongs, another third-class lever, have two levers (bars) with the fulcrum at the pivot end. The load consists of the food being picked up.
The human forearm is also a third-class lever. The fulcrum is found at the elbow, and the load is whatever object is held by the hand.
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