Other Free Encyclopedias » Science Encyclopedia » Science & Philosophy: Linear expansivity to Macrocosm and microcosm » Simple Machines - Levers, Mechanical Advantage, Pulleys, Wheel And Axle, Inclined Planes, Screws, Compound Machines - Wedges

Simple Machines - Levers

force fulcrum effort resistance

A lever is a simple machine that consists of a rigid bar supported at one point, known as the fulcrum. A force called the effort force is applied at one point on the lever in order to move an object, known as the resistance force, located at some other point on the lever. A common example of the lever is the crow bar used to move a heavy object such as a rock. To use the crow bar, one end is placed under the bar, which is supported at some point (the fulcrum) close to the rock. A person then applies a force at the opposite end of the crow bar to lift the rock. A lever of the type described here is a first-class lever because the fulcrum is placed between the applied force (the effort force) and the object to be moved (the resistance force).

The effectiveness of the lever as a machine depends on two factors: the forces applied at each end and the distance of each force from the fulcrum. The farther a person stands from the fulcrum, the more his or her force on the lever is magnified. Suppose that the rock to be lifted is only one foot from the fulcrum and the person trying to lift the rock stands 2 yd (1.8 m) from the fulcrum. Then, the person's force is magnified by a factor of six. If he or she pushes down with a force of 30 lb (13.5 kg), the object that is lifted can be as heavy as 180 (6 x 30) lb (81 kg).

Two other types of levers exist. In one, called a second-class lever, the resistance force lies between the effort force and the fulcrum. A nutcracker is an example of a second-class lever. The fulcrum in the nutcracker is at one end, where the two metal rods of the device are hinged together. The effort force is applied at the opposite ends of the rods, and the resistance force, the nut to be cracked open, lies in the middle.

In a third-class lever, the effort force lies between the resistance force and the fulcrum. Some kinds of garden tools are examples of third-class levers. When you use a shovel, for example, you hold one end steady to act as the fulcrum, and you use your other hand to pull up on a load of dirt. The second hand is the effort force, and the dirt being picked up is the resistance force. The effort applied by your second hand lies between the resistance force (the dirt) and the fulcrum (your first hand).


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over 3 years ago

i need the pictuers of levers please

and this is good information

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over 2 years ago

i'm looking for the resistance

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over 3 years ago

nice discription

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over 5 years ago

this is very good information

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over 3 years ago

thank you

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about 5 years ago

I'm looking for thrid class levers?

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over 5 years ago

very good and useful info!! :]

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over 6 years ago

this is good information good job

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over 1 year ago

paki bigay po ang efr nila :tweezer nutcracker pliers grass shear wheel barrow bread tong claw hammer fruit peller lemon squeezer tnx

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over 1 year ago

I need pics

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over 1 year ago

did not help at all

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over 1 year ago

Not imformative

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over 1 year ago

paki bigay po ang efr nila :tweezer nutcracker pliers grass shear wheel barrow bread tong claw hammer fruit peller lemon squeezer tnx

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over 1 year ago

paki bigay po ang efr nila :tweezer nutcracker pliers grass shear wheel barrow bread tong claw hammer fruit peller lemon squeezer tnx

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over 1 year ago

paki bigay po ang efr nila :tweezer nutcracker pliers grass shear wheel barrow bread tong claw hammer fruit peller lemon squeezer tnx

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over 1 year ago

paki bigay po ang efr nila :tweezer nutcracker pliers grass shear wheel barrow bread tong claw hammer fruit peller lemon squeezer tnx

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over 1 year ago

paki bigay po ang efr nila :tweezer nutcracker pliers grass shear wheel barrow bread tong claw hammer fruit peller lemon squeezer tnx

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over 1 year ago

paki bigay po ang efr nila :tweezer nutcracker pliers grass shear wheel barrow bread tong claw hammer fruit peller lemon squeezer tnx

Vote down Vote up

over 1 year ago

paki bigay po ang efr nila :tweezer nutcracker pliers grass shear wheel barrow bread tong claw hammer fruit peller lemon squeezer tnx

Vote down Vote up

over 1 year ago

paki bigay po ang efr nila :tweezer nutcracker pliers grass shear wheel barrow bread tong claw hammer fruit peller lemon squeezer tnx

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over 2 years ago

hahahaha what do you think this is too much about a lever this paragraph needs me too cry them a river