LEVERS AND PULLEYS
Levers
Levers are the basic tools used in from historic times. Levers were first described by Archimedes (287-212 BC). A lever is a simple tool that makes work easier; it involves moving a load around a pivot using a force. Many of our basic tools use levers, including scissors, pliers, hammer claws, nut crackers and many more others. In a Type 1 Lever, the pivot (fulcrum) is between the effort and the load. In an off-center type one lever, the load is larger than the effort, but is moved through a smaller distance.
Levers are used to lift heavy weights with the least amount of effort. In the example opposite, the heavy weight on the left hand side is been lifted by the person because of the lever. The longer the ‘rod’ the easier it is to lift the weight. Under normal circumstances the person would not be able to lift the weight at all. The fulcrum is the place where the rod pivots (or rotates). The load is the scientific name for the weight. The effort is quite simply the amount of effort used to push down on the rod in order to move the weight.
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Ra = Fb |
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Ra = F(a + b) |
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R(a + b) = Fa |
Pulleys
Pulley systems are used to lift large masses to tall heights. The pulley system consists of one or more pulleys and a rope or a cable. The number of pulleys used may increase or decrease the mechanical advantage of the system. The higher the mechanical advantage is, the easier it is to lift the object.
The pulley is a simple machine that consists of a grooved wheel and a rope providing a mechanical advantage in lifting a heavy load. There is a direct relationship between the number of ropes that form the pulley and its resulting advantage.
There are two basic types of pulleys. When the grooved wheel is attached to a surface it forms a fixed pulley. The main benefit of a fixed pulley is that it changes the direction of the required force. A fixed pulley provides no concrete mechanical advantage. The same amount of force is still required, but just may be applied in another direction. Another type of pulley, called a movable pulley, consists of a rope attached to some surface. The wheel directly supports the load, and the effort comes from the same direction as the rope attachment. A movable pulley reduces the effort required to lift a load.
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F = RP = 2F cosα/2 |
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G = 2Fcosα / 2 |
Calculating forces in the pulley
See also: Propeller calculation
