Museum of Science and Industry

Build a Lever

See how simple machines like a lever can help us do work.

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Lesson at a glance

The simplest of machines are designed to make work easier. In the realm of mechanical energy (energy of movement), machines make it easier for us to move something across a distance. Students investigate how a lever, a type of simple machine, makes work easier.

Students Will Know:
Mechanical advantage (MA) - A number that tells how much help using a simple maching provides. The larger the number, the more efficient the machine is at helping to do the job.

Students Will Be Able To:
Construct a lever and label its fulcrum, effort arm and resistance arm
Explain how the position of the fulcrum affects the work required to raise the resistance arm
Extension: Calculate the mechanical advantage using the length of the effort and resistance arms.

Illinois Learning Standards

Late Elementary:
State Goal 11: A.2b; A.2d
State Goal 12: D.2b
State Goal 13: A.2b; A.2c; B.2a; B.2b; B.2c
Middle / Junior High School:
State Goal 11: A.3a-g
State Goal 12: C.3a; D.3a
State Goal 13: A.3c

Extension

Calculate: How Much Help? The <i>mechanical advantage</i> (MA) of a simple machines tells us how many times the machine multiplies the effort we put into doing the work. You can calculate the MA by dividing the length of the effort arm (E) by the length of the resistance arm (R). Try this for the experiments you did and record your results in the table below. Measure the length of the effort arm – the distance from the 30 cm end of the ruler to the fulcrum (pencil) – and record it in the table. Measure the length of the resistance arm – the distance from the 0 cm end of the ruler to the fulcrum – and record it in the table. (Hint: the sum of the effort arm and resistance arm always equals 30 cm.)

What do you notice about the relationship between the MA and the number of pennies needed to lift the load each time?

The greater the mechanical advantage number, the easier it is to lift the object. This is because the MA tells us how many times the machine multiplies the effort we put into doing the work. For example, an MA of 3 means the machine is providing three times the effort that we put in to lift the object. The larger the number, the more help we get!