Mechanical Advantage and Efficiency

Mechanical Advantage A machine’s MA is the number of times a force exerted on a machine is multiplied by the machine. The MA is a ratio between the output and input force MA = Output Force / Input Force

If you exert a force of 20 N on a can opener, and the opener exerts a force of 60 N on the can, the ideal mechanical advantage of the can opener is 6 2 1200 3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Mechanical Advantage > 1 A machine with a mechanical advantage of greater than 1 multiplies the input force. Examples: can opener a ramp

Mechanical Advantage < 1 A machine with a mechanical advantage of less than 1 does not multiply the force but increases the distance and speed. Example: Hockey Stick Paper Fan

Mechanical Advantage = 1 A machine with a mechanical advantage of 1 means that a machine changes the direction of the force. Example: Rope

The mechanical advantage of a machine that changes only the direction of force is 1 Less than 1 Greater than 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Efficiency of Machines To calculate the efficiency of a machine, divide the output work by the input work and multiply the result by 100 percent. Efficiency = Output work * 100% Input work

The efficiency of a machine compares Force to mass Output work to input work. Force to friction Friction to mass 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Actual Mechanical Advantage The actual mechanical advantage is the mechanical advantage that a machine provides in a real situation.

Ideal Mechanical Advantage The ideal mechanical advantage is the mechanical advantage of a machine without friction. The more efficient a machine is, the closer the actual mechanical advantage is to the ideal mechanical advantage.

An ideal machine would have an efficiency of 1 percent 10 percent 50 percent 100 percent 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

If tight scissors have an efficiency of 50 percent, how much of your work is wasted overcoming friction? All of it None of it One half of it 10 percent of it 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Without friction there would be Less machine efficiency. Greater output work than input work. Greater input work than output work. Equal input and output work. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32