Page 24 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

Chapter 1 Introduction to Mechanisms and Machines 5

FIGURE 1-2 Balanced first class lever with different forces

In order to balance the equation (and the seesaw), d must be 15 ft. Although Fido
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and Fluffy helped us illustrate this point, the forces F and F can be anything—boxes,
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birds, buildings . . . you name it.
So, the lighter cat can balance a dog five times her weight if she just scoots back
farther. You’ll also notice that if Fido and Fluffy start seesawing, or pivoting on the
fulcrum, Fluffy will go up higher because she is farther from the pivot point. I’ll call the
distance from the ground to Fluffy’s highest point the travel (see Figure 1-3).

So the lightweight cat can lift the heavy dog, but she must travel farther to do it. This
is how levers give us mechanical advantage: A smaller force traveling through a longer
distance can balance a heavier force traveling a shorter distance. We could also say
the lighter cat is using a 5:1 mechanical advantage to lift the heavy dog by being five
times farther from the fulcrum. In our example, the travel of the light cat Fluffy (F ) is
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five times that of the heavy dog Fido (F ).
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There are many places you can see levers at work every day. A hammer claw acts as a
first class lever when pulling a nail out of a board (see Figure 1-4). You pull at the far
end of the hammer handle with a light force, so a big force pulls the nail out with the
hammer claw that is just a short distance from the hammer head. The hammer head
creates a pivot point that acts as the fulcrum.