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

A. B. C. D.

5%

86%

5%5%

A. 6

B. 2

C. 1200

D. 3

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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

A. B. C. D.

43%

4%

13%

39%A. 1

B. Less than 1

C. Greater than 1

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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

A. B. C. D.

5%0%0%

95%A. Force to mass

B. Output work to input work.

C. Force to friction

D. Friction to mass

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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

A. B. C. D.

4%

87%

9%

0%

A. 1 percent

B. 10 percent

C. 50 percent

D. 100 percent

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If tight scissors have an efficiency of 50 percent, how much of your

work is wasted overcoming friction?

A. B. C. D.

0%5%

90%

5%

A. All of it

B. None of it

C. One half of it

D. 10 percent of it

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Without friction there would be

A. B. C. D.

30% 30%

9%

30%

A. Less machine efficiency.

B. Greater output work than input work.

C. Greater input work than output work.

D. Equal input and output work.

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