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Simple Machines

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A washing machine with the highest energy rating may not always save ... Machines Have you ever tried to open a door by turning the doorknob s shaft instead of ... – PowerPoint PPT presentation

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Title: Simple Machines


1
Simple Machines
  • Chapter 14

2
What do All These Things Have in Common?
3
Questions
  • What is the function of the machines?
  • How many moving parts do they have?
  • How do the parts work together?
  • How does this machine make work easier?

4
Machines change the Way Force is Applied
  • A machine is any device that helps people do
    work.
  • They change the way in which work is done.

5
How Could we Move this Couch Easier?
6
Machines
  • If machines do not reduce the amount of work
    required, how do they help people do work?
    Machines make work easier by changing
  • The size of the force needed to do the work and
    the distance over which the force is applied.
  • The direction in which the force is exerted.

7
Have you ever tried to open a door by turning the
doorknobs shaft instead of the handle?
  • The doorknob allows you
  • to use less force to turn
  • the handle instead of the
  • shaft.

8
Machines Changing Size Direction
  • The doorknob is a machine. It allows you to
    apply a smaller force over a greater distance.
  • The boy using the rake
  • is a machine. He moves
  • his hands a short distance
  • to move the end of the
  • rake a large distance,
  • Allowing him to rake more
  • Leaves.

9
Machines
  • Input Force is the force exerted on a machine.
  • Output Force is the force that a machine exerts
    on an object.
  • Picture on page 450

10
Changing Direction
  • Machines also help you work by changing the
    direction of force.
  • You pull down on a rope
  • and the flag moves up.

11
Mechanical Advantage
  • When machines help you work, there is an
    advantageor benefit to using them?
  • Mechanical Output Force
  • Advantage Input Force

12
Mechanical Advantage
  • For machines that allow you to apply less force
    over a greater distance such as a doorknob the
    output force is greater than the input force.
  • Therefore, the mechanical advantage of this type
    of machine is greater than 1.
  • For example, if the input force is 10 newtons and
    the output force is 40 newtons, the mechanical
    advantage is
  • 40 N / 10 N
  • MA 4

13
Mechanical Advantage
  • Sometimes changing the direction of the force is
    more useful than decreasing the force or
    distance.
  • Therefore, the mechanical advantage of the
    machine is 1.

14
Practice Problem
  • The output force of a machine is
  • 600 N and the input force is 200 N. What is
    the mechanical advantage of the machine?
  • MA Output force 600 N 3
  • Input Force 200 N

15
Work Transfers Energy
  • Machines transfer energy to objects on which they
    do work!

16
Energy
  • When you lift an object, you transfer energy to
    it in the form of gravitational potential energy
    that is, potential energy caused by gravity

17
Work
  • When you use a machine to do work, there is
    always an exchange, tradeoff, between the force
    you use to do the work and the distance over
    which you apply that force.

18
Mountain ClimbingPage 453
  • Short Route Climbing straight up covers a
    shorter distance but more force must be applied
    against gravity
  • Long Route Climbing a gentle slope, the climber
    covers more distance but uses less force.

19
Efficiency
  • The work you put into a machine will always be
    greater than the work done by the machine. Some
    input work is always lost in overcoming friction.
  • Efficiency () Output work x 100
  • Input work

20
Efficiency and Energy
  • Work transfers energy and that machines make work
    easier.
  • Work transfers energy and that machines make work
    easier.

21
Energy Efficiency
  • Many appliances come with energy guides that can
    help a buyer compare the energy efficiency of
    different models.
  • A washing machine with the highest energy rating
    may not always save the most energy, because
    users may have to run those machines more often.

22
Review Questions
  • In what ways can a machine change a force?
  • By changing the size of a force, changing its
    direction, or both
  • How is a machines efficiency calculated?
  • Efficiency () Output work x 100
  • Input work
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