Page 32 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

Chapter 1 Introduction to Mechanisms and Machines 13

FIGURE 1-14 Pulley arrangements that give a 3:1 mechanical advantage

weight being suspended. So in this case, each part of the rope carries one-third of the
weight, and that is the mechanical advantage we feel when pulling on the rope: It’s
three times easier to lift the weight using this arrangement than it would be to lift the
weight on our own. That’s a 3:1 mechanical advantage.

TIP If you count the number of parts of rope going to and from the
movable pulley that suspends the weight, you can figure out the mechanical
advantage. If there are three pieces of rope going to and leaving one
movable pulley, the mechanical advantage is 3:1.

Another way to get the same 3:1 mechanical advantage is by using three simple
pulleys, rather than one simple and one compound pulley. You can see this
arrangement in the right image of Figure 1-14. The more pulleys you add to the
system, the more mechanical advantage you can get.
Pulley systems can get pretty complex and allow you to do things like lift a piano to
guide it into a second-story window with significantly reduced effort (though you
might be pulling for a very long time).