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Work_ Power_ _amp; Machines


 Define work and identify the units
 Describe the conditions that must exist for a force to
  do work on an object
 Calculate the work done on an object
 Describe and calculate power
 Compare the units of watts and horsepower as they
  relate to power
 Definition
     - quantity of energy transferred by a ______
  when it is applied to a body and causes that body to
  _________ in the ___________ of force

 Formula
     - ___________

 Units
     - Newton meter (____) or a joule (__)
               Work Continued
 Two factors
    1. size of _______, and ________ it is applied
          ex: pulling a suitcase

          * any part of a force that does not act in the
          direction of motion does no work on an
     2. ___________ of something by that force
                  Work Cont.
- weight lifter who holds a barbell weighing 1000 N
  does NO ________
- Why?
  - he may get very tired, but if the barbell is not
  moved by the force he exerts, he does no work on
  the barbell
  - work is done on his ________ when he raises the
               Work Problems
Q: A crane uses an average force of 5200 N to lift a
 girder 25 m. How much work does the crane do on
 the girder?

Q: While rowing in a race, John uses his arms to exert
 a force of 165 N per stroke while pulling the oar
 0.800 m. How much work does he do in 30 strokes?
           Work Problems Cont.
Q: Jake, a 235 N track athlete completes his race,
 which totals 15750 J, what is the total distance Jake

Q: Joey, performed 900 J of work, while lifting a box
 12 meters. What force did Joey exert on the box?

 Definition
     - a quantity that measures the ____ at which
  ______ is done

 Formula
     - P = ______

 Unit
     - Joule per second (____) or _______ (W)
     - Horsepower (___) = 746 W
              Power Problems
Q: Using a jack, a mechanic does 5350 J of work to
 lift a car 0.500 m in 50.0 s. What is the mechanic’s
 power output?

Q: Anna walks up the stairs on her way to class, She
 weighs 565 N and the stairs go up 3.25 m vertically.
 Calculate he power output if she climbs the stairs in
 12.6 s. What is her power output if she climbs the
 stairs in 10.5 s?
 Describe what a machine is and how it makes work
 Relate the work input to a machine to the work
  output of the machine
 Compare a machines actual mechanical advantage to
  its ideal mechanical advantage
 Calculate the ideal and actual mechanical and actual
  mechanical advantages of various machines
 Explain why efficiency of a machine is always less
  than 100%
 Calculate the machines efficiency
 Definition
     - a device that changes __________

 How does a machine change force
    - 3 ways a machine makes work easier to perform
         - change the _____ of _________ needed
         - the ________ of a force
         - the __________ over which a force acts
            Changing the Force
 Increasing the force you applied

  - small force exerted over a large distance becomes a
  ________ _______ exerted over a ________
           Changing the Distance
 Increasing distance

- small movement of oar at the hands makes a large distance
  the oar in the water will move.

*remember the trade off ________ distance _________ force*
          Changing the Direction
 Changing the direction of the applied force

     - pulling back on the handle of the oars causes its
  other end to move in the opposite direction.
                  Work Input
 Work Input
  - the _______ _______ on a machine as the _______
  ________ acts through the ________ ____________
      - input force: ________ exerted on a machine
      - input distance: _________ the input force acts
  - equals the input force multiplied by the input
            - input __________ < output ___________
            - input __________ > output ___________
                  Work Output
 Work Output
  - the ________ done by a machine as the output
  force acts through the output __________
      - output force: force exerted by a machine
      - output distance: distance the output force is
      exerted through

*due to friction the work done by a machine is always
  _______ than the work done on the machine
         Mechanical Advantage
 Definition
  - a quantity that measures how much a machine
      multiplies __________ or ___________
 Two types
    __________: measures the actual forces action on
     a      machine
      - AMA =

   __________: measures the mechanical advantage
    in the absence of _________
    - IMA =
     Mechanical Advantage Problems
Q: Alex pulls on the handle of a claw hammer with a force of 15
  N. If the hammer has a actual mechanical advantage of 5.2,
  how much force is exerted on a nail in the claw?


Q: If you exert 100 N on a jack to lift a 10,000 N car, what
  would be the jack’s actual mechanical advantage (AMA)

  Mechanical Advantage Problems
Q: Calculate the ideal mechanical advantage (IMA) of
 a ramp that is 6.0 m long and 1.5 m high?


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

         Efficiency of Machines
 Definition
     - a quantity, usually expressed as a
  ___________, that measures the ratio of _________
  work input
 Formula
     - Efficiency =

 - % of work input that becomes work output
 - due to friction, efficiency of any machine is always
 less than _________
            Efficiency Problems
Q: Alice and Jim calculate that they must do 1800 J of
 work to push a piano up a ramp. However, because
 they must also overcome friction, they must actually
 do 2400 J of work. What is the efficiency of the

Q: If the machine has an efficiency of 40%, and you do
 1000 J of work on the machine, what will be the work
 output of the machine?
 Name, describe and give an example of each of the
  six types of simple machines
 Describe how to determine the ideal mechanical
  advantage of different types of simple machines
 Define and identify compound machines
 Recognize simple machines within compound
              Simple Machines
 Definition
     - one of the six basic types of machines

 2 types or families
 Definition
  - a rigid bar that is free to move around a fixed point
- all levers have a rigid arm that turns around a point
  called the __________
- force is transferred from one part of the arm to
- original input force can be multiplied or redirected
  into output force
- levers are divided into __ classes, based on the
  locations of the input force, output force, and the
              Lever Family Cont.
 3 classes
      1. First class
             - fulcrum is in the ___________ of an arm
             - the input force acts on one end
             - the other end applies an output force
             - MA can be <1, >1, =1

      2. Second class
            - _________ is at one end of the arm
            - input force is applied to the other end
            - output force is in the __________
            - MA will always be greater than 1
       Lever Family Cont.
3. Third class
      - input force is in the _________
      - output force is one one end
      - fulcrum is on the other end
      - multiply distance rather than
      MA always ____ 1
            Wheel and Axis
 Definition
  - simple machines that consist of two ________
  or cylinders, each one with a different radius
- made of a level or a pulley (_________)
  connected to a shaft (______)
- small input force, multiplied to become a large
  output force
                Inclined Planes
 Definition
  - slanted surface along which a force moves an
  object to a different elevation
      ex. knife, ax, zipper, wedge, screw
- ramp __________ the force applied to lift object
- turns a small input force into a large output force by
  spreading the work out over a large ___________
  - wedge: functions as _____ inclined planes back to
      back, turning a downward force into two forces
      directed out to the sides
 Definition
   - a simple machine that consists of a rope that fits
   into a groove in a wheel.
- very similar to a lever
    - point in the middle of the pulley is like a fulcrum
    - rest of the pulley acts like the rigid arm

 3 Types of Pulleys
  - ________ pulleys
  - ________ pulleys
  - ________ system
              Types of Pulleys
- fixed pulleys: changes the ___________ of the input

- moveable pulleys: changes both the ________ and
  the _________ of the input force

- pulley system: made of both fixed and moveable
          Compound Machines
 Definition
     - a machine that is made of more than one simple

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