a lever of the third class has mechanical advantage less than one.Why then do we use it?

Question

the differences in the other lever oders

Answer 1

The force times the distance remains constant when you use a machine. So if a machine multiplies your force, it will decrease the distance you move the object. For instance jacking up a car makes the force large, but the car moves very little.

A 3rd class lever does the opposite, it makes the force smaller (so its mechanical advantage is less than one), but it makes the distance moved greater.

An example would be a hockey stick. Very lttle force is actually delivered to the puck, but it moves a large distance quickly when it is swung.

Answer 2

Mechanical advantage less than unity simply means the output motion is magnified with respect to the input motion.

This has a lot of common applications, such as the hockey stick example given by Thomas G in his answer. Some others include: bourdon tube pressure measuring meters, which amplify with levers and gears the small motion of the bourdon tube to drive a meter dial; all mechanical clock movements using spring-stored energy to drive the clock hands; trebuchets and catapults. In the case of the latter, a mechanical “advantage” of less than one results in a faster moving projectile.

Now that we’ve jogged your mind, I’m sure with a little reflection you can think of many more examples.

Answer 3

increased distance.

If advantage is 1/10, then distance traveled is 10 times.