Simple Machines Efficiency Comparison Quiz

Ideal and Actual Machines

• An ideal machine has no loss of energy in any form, and work output equals work input.
• An actual machine always has some loss of energy.

Levers

• In a Class II lever, the effort is between the fulcrum and the load, so the effort arm is always smaller than the load arm, resulting in a Mechanical Advantage (M.A.) < 1.
• In a Class III lever, there is no gain in force, but there is a gain in speed, with a longer displacement of the load obtained by a smaller displacement of the effort.

Examples of Levers

• A bottle opener is a Class II lever, with the load in the middle, fulcrum at one end, and effort at the other.
• Sugar tongs are a Class III lever, with the effort in the middle, load at one end, and fulcrum at the other.
• The human arm is a Class III lever, with the elbow as the fulcrum, biceps exerting the effort, and the load on the palm.
• Raising the weight of the body on toes is an example of a Class II lever, with the fulcrum at the toes, load in the middle, and effort by muscles at the other end.

Pulleys

• A fixed pulley is a pulley with a fixed axis of rotation, used to change the direction of the force applied.
• The ideal mechanical advantage of a single fixed pulley is 1, with no gain in mechanical advantage.
• A single movable pulley has a mechanical advantage of 2 in the ideal case.
• The efficiency of a single movable pulley system is not 100% due to friction and the weight of the pulley and string.

Machines

• A machine is a device that allows us to overcome a large resistive force or obtain a gain in speed.
• An ideal machine has no dissipation of energy, with an efficiency of 100%.
• Machines are useful for lifting heavy loads, changing the point of application of effort, changing the direction of effort, and obtaining a gain in speed.