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Increasing Speed with a Lever

by Ron Kurtus (revised 25 June 2016)

You can use a Class 1 or Class 3 lever to increase the speed that the load moves, according to where the fulcrum is located. To increase the speed, the length of the load arm of the lever must be greater than the length of the effort arm.

The equation for the speed of the load or effort relates to the speed mechanical advantage of the lever. From the equation, you can determine an unknown speed or length.

Questions you may have include:

This lesson will answer those questions. Useful tool: Units Conversion



Using Class 1 or Class 3 lever

You can increase the speed at which a load moves as compared to the speed of the effort by using either a Class 1 or a Class 3 lever. These levers can be used as a catapult to project an object at a high speed.

Increase the speed the load moves with a Class 1 lever

Increase the speed the load moves with a Class 1 lever

You could use such a lever to to project an object at a high speed. However, what you gain in speed requires a greater effort force. Thus in many cases, the Class 1 lever is used, because pushing down with your weight is easier than pulling up.

Increase the speed the load moves with a Class 3 lever

Increase the speed the load moves with a Class 3 lever

Since the load or output length (dO) is longer for a given lever length, the Class 3 lever would result in a greater speed mechanical advantage and be able to project the object faster.

Speed equation

The relationship between the effort speed and load speed is dependent on the ratio of the arms of the lever, according to the equation:

SO/SI = dO/dI

where

Note that SO/SI is the speed mechanical advantage of the lever.

(See Speed Mechanical Advantage for more information.)

Application

Suppose you wanted to project an object to a speed of 10 meters/second with a lever that is 2 meters long. The length of the load or output arm is 1.5 m and the length of the effort or input arm is 0.5 m. What effort speed must you use?

SO/SI = dO/dI

Solve for SI:

SI = SOdO/dI

Substitute values:

SO = 10 m/s

dO = 1.5 m

dI = 0.5 m

SI = 10*(0.5)/1.5 = 3.33 m/s

Summary

You can use a Class 1 or Class 3 lever to increase the speed of the load, according to where the fulcrum is located. To increase the load speed, the length of the load arm of the lever must be greater than the length of the effort arm.

The equation for the speed of the load or effort relates to the speed mechanical advantage of the lever. The speed equation is:

SO/SI = dO/dI

From the equation, you can determine an unknown speed or length.


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