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14.3.1 Compare a machine’s AMA to its IMA. 14.3.2 Calculate the AMA and IMA of various machines. 14.3.3 Explain why the efficiency of a machine is always less than 100%. 114.4.4 Calculate a machine’s efficiency. Objectives.

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objectives
14.3.1 Compare a machine’s AMA to its IMA.

14.3.2 Calculate the AMA and IMA of various machines.

14.3.3 Explain why the efficiency of a machine is always less than 100%.

114.4.4 Calculate a machine’s efficiency

Objectives
slide2

How does the actual mechanical advantage of a machine compare to its ideal mechanical advantage?

The mechanical advantageof a machine is the number of times that the machine increases an input force.

Because friction is always present, the actual mechanical advantage of a machine is always less than the ideal mechanical advantage.

Mechanical Advantage

slide3

Mechanical Advantage

Actual Mechanical Advantage

The mechanical advantage determined by measuring the actual forces acting on a machine is the actual mechanical advantage.

The actual mechanical advantage (AMA) equals the ratio of the output force to the input force.

slide4

Mechanical Advantage

A loading ramp is a machine used to move heavy items into a truck.

The mechanical advantage of a ramp with a rough surface is less than that of a similar smooth ramp because a greater force is needed to overcome friction.

slide5
A nutcracker is a machine that converts the input force applied to it into a larger force capable of cracking a nut.

Because it increases force, the nutcracker has a mechanical advantage greater than 1.

slide6

Mechanical Advantage

Ideal Mechanical Advantage

The ideal mechanical advantage (IMA) of a machine is the mechanical advantage in the absence of friction.

Because friction reduces mechanical advantage, engineers often design machines that use low-friction materials and lubricants.

slide8

Calculating Mechanical Advantage

The cable supporting the gondola forms an inclined plane, a type of machine. The inclined plane is used to move people up to the top of the mountain.

slide9

Calculating Mechanical Advantage

The gondola uses the inclined plane formed by its supporting cable to more easily move people uphill.

  • The increased horizontal distance (input distance) is greater than the vertical gain in height (output distance).
  • The inclined cable gives the gondola a ideal mechanical advantage greater than 1.
  • A ramp is an inclined plane.
slide10

Calculating Mechanical Advantage

Calculating IMA

A woman drives her car up onto wheel ramps to perform some repairs. If she drives a distance of 1.8 meters along the ramp to raise the car 0.3 meter, what is the ideal mechanical advantage (IMA) of the wheel ramps?

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Calculating Mechanical Advantage

Read and Understand

What information are you given?

slide12

Calculating Mechanical Advantage

Plan and Solve

What formula contains the given quantities and the unknown?

Replace each variable with its known value and solve.

slide13

Calculating Mechanical Advantage

Look Back and Check

Is your answer reasonable?

The IMA must be greater than 1 because the input distance is greater than the output distance. The calculated IMA of 6 seems reasonable.

slide14

Calculating Mechanical Advantage

1.A student working in a grocery store after school pushes several grocery carts together along a ramp. The ramp is 3 meters long and rises 0.5 meter. What is the ideal mechanical advantage of the ramp?

slide15

Calculating Mechanical Advantage

1.A student working in a grocery store after school pushes several grocery carts together along a ramp. The ramp is 3 meters long and rises 0.5 meter. What is the ideal mechanical advantage of the ramp? Answer: IMA = Input distance/Output distance

IMA = 3 m/0.5 m = 6

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Calculating Mechanical Advantage

2.A construction worker moves a crowbar through a distance of 0.50 m to lift a load 0.05 m off of the ground. What is the IMA of the crowbar?

slide17

Calculating Mechanical Advantage

2.A construction worker moves a crowbar through a distance of 0.50 m to lift a load 0.05 m off of the ground. What is the IMA of the crowbar? Answer: IMA = Input distance/Output distance

IMA = 0.5 m/0.05 m = 10

slide18

Calculating Mechanical Advantage

3.The IMA of a simple machine is 2.5. If the output distance of the machine is 1.0 m, what is the input distance?

slide19

Calculating Mechanical Advantage

3.The IMA of a simple machine is 2.5. If the output distance of the machine is 1.0 m, what is the input distance? Answer: Input distance = (IMA)(Output distance)

Input distance = (2.5)(1.0 m) = 2.5 m

slide20

Why is the efficiency of a machine always less than 100 percent?

The percentage of the work input that becomes work output is the efficiencyof a machine.

Because there is always some friction, the efficiency of any machine is always less than 100 percent.

Efficiency

slide21

Efficiency

Efficiency is usually expressed as a percentage.

For example, if the efficiency of a machine is 75 percent, then you know that 75 percent of the work input becomes work output.

slide22

Efficiency

If a machine requires 10.0 J of work input to operate, then the work output is 75% of

10.0 J.

slide23

Efficiency

Reducing friction increases the efficiency of a machine.

Roller bearings reduce the friction of the rotating wheels because rolling friction is less than sliding friction.

To further reduce the rolling friction, the roller bearings are also lubricated with grease.

slide24

Efficiency

Engineers analyze the flow pattern of a smoke trail to determine the fluid friction forces (air resistance) acting on the vehicle. Engineers use these data to optimize a vehicle's shape for maximum fuel efficiency.

slide25

Assessment Questions

  • Which statement about the actual mechanical advantage of a machine is true?
    • The actual mechanical advantage is greater than one if the input force is greater than the output force.
    • The actual mechanical advantage of a machine is greater than its ideal mechanical advantage when the output force is greater than the input force.
    • The actual mechanical advantage of a machine is always less than its ideal mechanical advantage.
    • The actual mechanical advantage of a machine is never affected by friction.
slide26

Assessment Questions

  • Which statement about the actual mechanical advantage of a machine is true?
    • The actual mechanical advantage is greater than one if the input force is greater than the output force.
    • The actual mechanical advantage of a machine is greater than its ideal mechanical advantage when the output force is greater than the input force.
    • The actual mechanical advantage of a machine is always less than its ideal mechanical advantage.
    • The actual mechanical advantage of a machine is never affected by friction.ANS: C
slide27

Assessment Questions

  • If a lever raises a large rock 0.1 meters when the other end of the lever moves downward 2 meters, what is the ideal mechanical advantage of the lever?
    • 0.05
    • 0.5
    • 2
    • 20
slide28

Assessment Questions

  • If a lever raises a large rock 0.1 meters when the other end of the lever moves downward 2 meters, what is the ideal mechanical advantage of the lever?
    • 0.05
    • 0.5
    • 2
    • 20ANS: A
slide29

Assessment Questions

  • A machine is used to accomplish 300 J of work. If the efficiency of the machine is 60 percent, what is the necessary work input?
    • 180 J
    • 360 J
    • 500 J
    • 750 J
slide30

Assessment Questions

  • A machine is used to accomplish 300 J of work. If the efficiency of the machine is 60 percent, what is the necessary work input?
    • 180 J
    • 360 J
    • 500 J
    • 750 JANS: C
slide31

Assessment Questions

  • The efficiency of any machine is less than 100% because of losses due to friction.TrueFalse
slide32

Assessment Questions

  • The efficiency of any machine is less than 100% because of losses due to friction.TrueFalse

ANS: T