Ancient Principles Drive Mechanical Advantage

As complicated as some farm machinery is, it all comes down to combinations of levers working together to make farm work more efficient.

| November 2018

  • farm machinery
    A McCormick-Deering No. 9 mowing machine, a device chock-full of levers. Even the double tree is actually a second class lever with the weight being the load (mower) connected to the center hole of the evener.
    Photo by Sam Moore
  • simple lever
    Drawing One: A simple lever. Another example is the pitchfork: The hay on the tines is the load, the fulcrum is the hand grasping the fork handle near its center, and the force is other hand pushing down on the handle end to lift the hay.
    By the Farm Collector staff
  • different lever classes
    Drawing Two: Top, a class 1 lever; middle, a class 2 lever; bottom, a class 3 lever.
    By the Farm Collector staff
  • bellcrank lever
    Drawing Three: An angular (or bellcrank) lever.
    By the Farm Collector staff
  • compound lever
    Drawing Four: A compound lever.
    By the Farm Collector staff
  • continuous wheel lever
    Drawing Five: A wheel, axle and gear as a continuous lever.
    By the Farm Collector staff

  • farm machinery
  • simple lever
  • different lever classes
  • bellcrank lever
  • compound lever
  • continuous wheel lever

The 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.

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 complex 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. 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 overcome 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.



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