Let’s Talk Rusty Iron

Sam Moore

8 November 2018 Farm Collector

Ancient principles drive

mechanical

advantage

Farm machines are full of levers. For example, everyone

knows that the cutter bar on a horse-drawn mower is raised

by a lever, but how about the eveners that equalize the load

between the two horses pulling the thing? Or, the mower

wheels that impart motion to the cutter bar knife that cuts

the hay – could they be levers as well? The mower is a com-

plex machine, but it’s made up of a lot of levers in one form

or another. The evener, wheels and gears are really just levers

in disguise, as we shall see.

Force arm is the key

The simple lever consists of a rigid bar that rotates around

a fixed object called a “fulcrum,” as shown in drawing No.

1 (opposite page). The hand provides the force by pulling

down on the one end of the lever. The lever rotates around

the fulcrum and causes the weight at the other end of the

lever to rise. The length of the lever between the weight and

the fulcrum is the weight arm, while the force arm is the

length of the lever between the hand and the fulcrum.

If the weight arm and the force arm are the same length,

the amount of force necessary to lift the weight will be equal

to the weight and there will be no mechanical advantage. If

the force arm is twice as long as the weight arm, twice the

weight can be lifted with the same amount of force. A ton of

weight can be lifted with a force of only 100 pounds if the

force arm is 20 times as long as the weight arm, assuming

the lever itself has no weight and there is no friction at the

fulcrum.

Levers, of course, do more than lift weights. Levers over-

come any resistance, such as sliding a gear horizontally

along a shaft, as in a tractor transmission, or application

of pressure upon an object, such as with a pair of pliers or

tweezers.

Class 1 levers

There are three classes of simple levers, depending upon

the relative positions of the fulcrum, weight and applied

force (see drawing No. 2 opposite page).

T

he ancient Archimedes of Syracuse

(a Greek mathematician, physicist,

engineer, inventor and astronomer,

287-212 B.C.) is supposed to have said,

“Give me a firm place to stand and I will move

the earth.” Archimedes was talking about the use

of a lever and a fulcrum to move a heavy object.