Download energy,work, power, and machines

ENERGY,WORK, POWER,
AND MACHINES
IPC Spring 2008
Energy, Work, Power &
Machines
1. Energy is the ability to do work.
Potential energy – stored energy
or energy due to position
 PE=m g h
 m is mass (kg)
 g is gravity (9.8 m/s2)
 h is the height of the object (m)
Energy, Work, Power,&
Machines
 Kinetic energy – energy of
motion
 KE=1/2 mv2
 m is mass (kg)
 v is velocity (m/s)
Energy, Work, Power, &
Machines
 2. Energy conversion is a changing of
one form of energy to another.
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 3. The Law of Conservation of
Energy states that energy cannot be
created nor destroyed, but is only
changed from one form to another.
Energy, Work, Power, &
Machines
 4. Work is done when a object
moves through a distance because
of a force acting upon the object.
 5. The following formula is used to
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calculate work:
W=Fd.
W stands for the work done (J)
F stands for the force (N)
d stands for distance (m)
The SI unit for work is the joule (J).
Energy, Work, Power, &
Machines
 6. Power - the rate at which work is
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done.
7. Power can be calculated by using the
following formula:
P= W
or
P= Fd
t
t
P stands for power (W)
W stands for work (J)
t stands for time. (s)
The SI unit for power is the watt (W).
Energy, Work, Power, &
Machines
 8. A simple machine is a device
that changes the size or the
direction of force that is being
used to do work.
 9. The six classes of simple
machines are: inclined planes,
wedges, screws, levers, pulleys,
and wheels and axles.
Energy, Work, Power, &
Machines
10. An inclined plane is a machine that
has a sloping surface that is longer
than its vertical side.
11. A wedge is a modified inclined plane.
It has a thin or sharp end and a thicker
end.
 A screw has spiral threads wound
around a cylinder. The screw is a spiral
inclined plane.
Energy, Work, Power, &
Machines
 12.A lever is a bar that pivots around a
fixed point called a fulcrum.
 There are three classes of levers,
based on the positions of the effort
force, resistance force and fulcrum.
Fulcrum in the middle= 1st class lever
Resistance in the middle= 2nd class
lever
Effort in the middle= 3rd class lever
Energy, Work, Power, &
Machines
 13.A pulley is a machine that
changes the direction of a force. A
pulley is made up of a rope that
turns around a wheel.
 A wheel and axle is a machine
that has a larger effort wheel and
a small resistance wheel that turn
around the same pivot.
Energy, Work, Power, &
Machines
 14.The mechanical advantage is the
number of times a machine multiplies
an effort force. Mechanical advantage
can be calculated by the following
equations:
 AMA = Fr
IMA =
de
Fe
dr
 AMA = actual mechanical advantage (real life)
 IMA = ideal mechanical advantage (pretend)
 Fr = resistance force
 Fe = effort force d
r
de = effort distance
= resistance distance
Energy, Work, Power, &
Machines
15.The mechanical advantage of a
pulley system is determined by
counting the number of strands
of rope that support the
resistance force.
Energy, Work, Power, &
Machines
 16.Work input is always greater than
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work output due to friction.
Win= W out
Fe x de = Fr x d r
Win = work input (J)
W out = work output (J)
Fe = effort force (N)
de = effort distance (m)
Fr =force of the resistance (N)
d r=how far the resistance moved (m)
Energy, Work, Power, &
Machines
 17.Efficiency
is a measure of how
much of the work put into a machine is
changed to work put out by the
machine.
 Efficiency
is calculated using the
following formula:
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efficiency = W out x 100%
Win
 efficiency = AMA x 100%
IMA
Energy, Work, Power, &
Machines
 18. Compound machines
consist of two or more simple
machines.