Swinging mass M lifts mass 2M

The lifting force on mass A on the ground is +2mg(1-cos(θ)), so when θ is 60 degrees a mass of 500 g can lift a mass of 1 kg off the ground.
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All this equipment is commonly used. I suggest setting out a variety of masses so that professors can demonstrate other setups as desired. The 500 g mass barely lifts the 1 kg mass off the ground however it makes quite a loud noise that demonstrates that it does work.

Let them hold both masses and ask the question "can we lift the larger mass with the smaller mass without doubling over the ropes on the pulleys?" If you check this demo out take masses that are considerably less than the ones listed here if you intend to let the public anywhere near them. As always when you present a demo make sure you ask the participants questions before you demonstrate and after. Think about the concepts involved beforehand; having a friend ask you questions about it can be very revealing as to if you understand it well or not. Whenever you ask a question count to five (or at least three) in your head waiting for an answer before you stay anything else.