I need to split the cake so we can each have a piece.
This rock looks like a wedge. Maybe I can use it to split the cake.
Bob is celebrating his birthday.
Bob needs to solve his problem.
I could tie this rope around the rock to help lift it.
Bob looks around to see what he can use.
I'll put the rope over this branch like a pulley.
Bob found a heavy boulder. Can he lift it?
I could drop this heavy boulder on the wedge to split the cake.
Bob finds a rope.
Bob is using a pulley so he can use less force to lift the heavy boulder. He is using the mechanical energy from his arms to pull the rope. He pulls it slowly so he can use less power. The boulder has potential energy as it hangs over the cake.