Which of the following machines does not apply the lever principle?

Analyze the question: We need the machine that does not work on the lever principle (a rigid bar turning about a fixed pivot/fulcrum, with effort and load applied at different points).

Explain the concept: A lever has three parts: the fulcrum, the effort, and the load. Levers come in three classes:

• First class: fulcrum between effort and load (e.g. scissors, seesaw)
• Second class: load between fulcrum and effort (e.g. wheelbarrow, nut cracker)
• Third class: effort between fulcrum and load (e.g. sugar tongs, forceps, fishing rod)

Solution, option by option:

• A. Claw hammer: When pulling out a nail, the hammer pivots on its head. This is a lever (first class).
• B. Wheelbarrow: The wheel is the fulcrum, the load is in the middle, and the effort is at the handles. This is a second-class lever.
• C. Single pulley: A fixed single pulley is a wheel with a rope running over it. It only changes the direction of the effort and gives a mechanical advantage of 1. It is classed as a pulley system, not a lever, in the usual WASSCE treatment. (Strictly, a pulley can be modelled as a lever with equal arms, but it is not one of the standard "lever" machines.)
• D. Sugar tong: Two arms are joined at one end (the fulcrum), with the effort in the middle and the load at the other end. This is a third-class lever.

Answer: The single pulley is the one that does not apply the lever principle, so the answer is C.

Tip: For "which is not a lever" questions, look for a pivoting bar. Pulleys, inclined planes, screws, and gears are different simple machines, while hammers, barrows, tongs, scissors, and pliers are levers.