Block and tackle: Bosun's chair.

Block and Tackle: Professor in bosun's chair pulls himself up. The top part of a block and tackle (three pulleys each on both upper and lower parts) is attached near the ceiling of the classroom; the bottom part is attached to a canvas Bosun's chair which hangs a few feet above the ground. [Sailors use bosun's chairs to hoist themselves to the tops of masts.] The professor (or selected victim) sits and straps himself (or herself) in the bosun's chair, grabs the dangling rope, and pulls himself (or herself) up easily. The force required to pull a person up is 1/7 of their weight if the person is sitting in the chair and pulling himself up. However the force is 1/6 of the seated person's weight if a different person standing on the ground is pulling the rope. (For a proof of this, consult with Dr. Richard Packard (packard@socrates.berkeley.edu). NOTE: One must take care to NOT let go of the rope, especially when the person is hoisted high up in the air. Also, it is a good idea to NOT swing. Gloves (leather or cotton) should be worn to keep from getting blisters and abraded skin while handling the rope