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Cornell 14-3. Mechanical advantage Actual mechanical advantage Ideal mechanical advantage Calculating mechanical advantage Efficiency. A nutcracker is a machine that converts the input force applied to it into a larger force capable of cracking a nut.

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Cornell 14-3


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cornell 14 3

Cornell 14-3

Mechanical advantage

Actual mechanical advantage

Ideal mechanical advantage

Calculating mechanical advantage

Efficiency

slide2
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.

slide3

Mechanical Advantage and Efficiency

    • Mechanical Advantage- 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.
slide4
Actual Mechanical Advantage- The mechanical advantage determined by measuring the actual forces acting on a machine.
    • The actual mechanical advantage (AMA) equals the ratio of the output force to the input force.
slide5

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.

slide6
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.
slide7

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.

slide8

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 mechanical advantage greater than 1.
slide9

Calculating Mechanical Advantage

    • Formula for AMA:
      • Suppose you exert an input force of 10 N on a hand-held can opener, and the opener exerts an output force of 30 N on the can. What is the AMA of the opener?
      • The can opener triples your input force.
slide10
Formula for 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 .3 meter, what is the ideal mechanical advantage of the wheel ramp?

The ramp decreases the amount of force needed to raise the car up .3m but you have to drive a longer distance.

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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?
slide12

Efficiency-The percentage of the work input that becomes work output

    • Because there is always some friction, the efficiency of any machine is always less than 100 percent.
    • 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.
slide13

Formula:

    • You do 250,000J of work to cut a lawn with a hand mower. If the work done by the mower is 200,000 J, what is the efficiency of the lawn mower?
slide15
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.
slide16

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.

slide18

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.
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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
slide20

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
slide21

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
slide22

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
slide23

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
slide24

Assessment Questions

  • The efficiency of any machine is less than 100% because of losses due to friction.TrueFalse
slide25

Assessment Questions

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

ANS: T