Levers

A lever is a machine that consists of a bar or plane pivoting on a fulcrum. Levers have three main parts: The load, the fulcrum and the effort. The load is the object that is to be moved. The fulcrum is the point at which the lever pivots. The effort is the force that is used to move the lever.

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Levers work under the principle of conservation of energy. Remember that a joule of energy or work is equivalent to a newton times a metre. Since the amount of energy is the same for all forces on the lever, if the distance the object is required to move is greater, the force required to move it is smaller.

First and second class levers

In a first class lever, the fulcrum is located between the load and the effort. Some examples of first class levers are pliers, scissors and see-saws. In first class levers, the direction of the effort is opposite the direction of the load. In other words, the effort must push down on the lever to move the load upwards.

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In a second class lever, the load is located between the effort and the fulcrum. Some examples of second class levers are wheelbarrows, nutcrackers and bottle openers. In second class levers, the direction of the effort and the load are the same. In order to move the load upwards, the effort must be applied upwards as well.

First and second class levers are both force multipliers. Force multipliers reduce the force required to move an object. Force multipliers are said to provide mechanical advantage because they decrease the force that needs to be exerted. In a first or second class lever, the mechanical advantage can be increased by moving the load closer to the fulcrum and the effort farther away from the fulcrum.

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The mechanical advantage of a first or second class lever can be measured in two ways:

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Levers provide mechanical advantage by changing the distance over which force must be applied to move an object. If the distance between the fulcrum and the effort is increased, the distance that the effort must move the lever increases as well. Conversely, if the distance between the fulcrum and the load is decreased, the distance that the lever must move also decreases. Since work is directly proportional to force and distance, the greater the distance needed to move the lever, the smaller the force necessary to move the load.

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Third class levers

In a third class lever, the effort is between the load and the fulcrum. Some examples of third class levers include fishing rods, cricket bats and chopsticks. Third class levers are different from first and second class levers because instead of force multipliers, they are speed multipliers. This means they do not provide a mechanical advantage. In fact, more force is required in a third class lever to move an object.

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Third class levers are used in applications where speed is important. Because a larger force is applied by the effort, the load travels a further distance. Since the load travels a further distance, its speed is also multiplied.

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