Physics students work through a lot of homework problems involving compound pulleys, but I don’t think most people ever get hands-on experience with one. For the latest round of visits to Baltimore Talent Development High School, Nuala and I built something to give students a memorable appreciation for mechanical advantage. Using one strong rope, five pulleys, and two wooden bars, this contraption gives one side a 5 to 1 advantage over the other. One girl easily dragged five bodily struggling high school boys across the room.
Props to these guys for really throwing their weight into it, but they were no match. If you try this: Make sure you shell out for thick rope, solid pulleys, and rods that won’t snap. I attached the pulleys to the bar using carabiners held in place by wood screws.