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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
direction of force.
• You pull down on a rope
• and the flag moves up.

11
• Mechanical Output Force

12
• 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
• 40 N / 10 N
• MA 4

13
• 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