# Energy, Work, and Simple Machines - PowerPoint PPT Presentation

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## Energy, Work, and Simple Machines

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### Establish a coordinate system Draw a vector diagram. ... W = Fd For constant forces in the direction ... of one or more of the six simple machines ... – PowerPoint PPT presentation

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Title: Energy, Work, and Simple Machines

1
Chapter 10
• Energy, Work, and Simple Machines

2
10.1 Energy and Work
• Energy is the ability to produce change in itself
or the environment.
• Energy of Motion
• Rearranging
• Substituting Newtons second law
• vf2 - vi2 2Fd/m

3
• Multiply both sides by ½ m
• ½ mvf2 ½ mvi2 Fd
• Kinetic energy
• KE ½ mv2
• Work-Energy Theorem
• ?KE W
• When work is done on an object, a change in
kinetic energy results.

4
• Work
• Through the process of doing work, energy can
transfer from the environment to the object and
back again!
• The equation for work is
• W Fd
• For constant forces in the direction of the
motion.
• Unit of work is the joule (J)

5
• Constant force at an angle
• Work (angle between force and displacement).
• W Fd cos ?

6
• Power
• The rate at which work is done
• P W/t
• Power is measured in watts (joule/second)

7
PSS
• Sketch the problem.
• Establish a coordinate system
• Draw a vector diagram.
• List known and unknowns.
• Use the basic equation for work when a constant
force is exerted in the same direction as the
displacement. Or the equation W Fd cos ? which
will work in all situations.

8
• Use the work-energy theorem to determine the
change in energy of the system.
• Use work and time to find power.

9
10.2 Machines
• Simple and Compound Machines
• The output work can never be greater than the
input work
• The machine simply aids in the transfer of
energy.
• The force you exert on a machine is called the
effort force Fe
• The force exerted by the machine is called the
resistance force Fr

10
• The ratio of resistance force to effort force, is
• MA Fr / Fe
• This equation can be rewritten using the
definition of work
• Wo Wi or
• Frdr Fede
• Rearranging this gives
• Fr/Fe de/dr

11
• We know that the mechanical advantage is given by
MA Fr/Fe
• For an ideal machine, MA de/dr
• Because this equation is characteristic of an
ideal machine, the mechanical advantage is called
• IMA de/dr

12
• Efficiency
• The efficiency of a machine is defined as the
ratio of output work to input work.
• Efficiency () Wo/Wi X 100
• An ideal machine has equal output and input work
and the efficiency is 100.
• In terms of mechanical advantage and ideal
• Efficiency () (Fr/Fe)/(de/dr) X 100
• Efficiency () MA / IMA X 100

13
• Simple machines
• Most simple machines are combinations of one or
more of the six simple machines.
• They are the lever, pulley, wheel and axel,
inclined plane, wedge, and screw.
• The IMA of all machines is the ratio of distances
moved.

14
• Compound machines
• A compound machine consists of two or more simple
machines linked so that the resistance force of
one machine becomes the effort force of the
second.
• The mechanical advantage of a compound machine is
the product of the mechanical advantage of the
simple machines it is made up of.
• MA MA machine 1 X MA machine 2