On this Voyage of Discovery, overcast skies on Day Five nearly forced Ben and Brandon to abandon their celestial tracking project in favor of this topic. We got as far as setting up the experiment, but ultimately the sunlight broke through the clouds and the experiment was not used.
When we do conduct experiments in mechanical advantage, we rig a block-and-tackle system designed to lift a fixed weight -- often a lead ballast ingot (safely wrapped in canvas) -- a few inches off the deck, using from one to four pulleys to distribute the load. As students haul on the line, a spring scale measures how many pounds of force must be exerted to lift the weight. As an interesting side wrinkle, our spring scale can only measure up to 50 pounds, and the ingot weighs considerably more. Thus, students must extrapolate the ingot's true weight from their findings.
In theory, each down-pulling pulley doubles this simple machine's mechanical advantage. In practice, however, the friction of the lines and pulleys counteract this advantage. The effect of friction is negligable at first, but it gradually increases as more pulleys are added, ultimately canceling out any mechanical advantage gained -- thus placing limits on the machine's effectiveness, no matter how many additional pulleys are added.