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Work and Power
CH 14.1
True
False
Statement
Work is the product of force, distance and
time
Power is the amount of work done in a certain
time
Horsepower, is compared to an actual horse’s
power
The SI unit for work is the watt
The SI unit for power is the joule
True
False
Work
 Work is the product of force and distance
 Force is unbalanced
Work
Requires Motion
Depends on Direction
 Some of the force must
 Forces act in the same
act in the same
direction as the object
moves
direction as the
movement
 Force that does not act
in the direction of
motion does not do
work on an object
 No movement = no
work
Calculating Work
 How much work is done
 SI Units



W= J, joule
F=
d=m
by a weight lifter who
lifts 1600N over his
head, at a height of 2m?
 Given:
 Formula:
 Solve:
Power
 Power- rate of doing
work
 Work at a faster rate =
increasing power
 Increase power


More work in a given time
More work in less time
Calculating Power
 You exert a force of 72N
 SI Units

P= W, watt



= 1J per s
W= J
t= s
to lift a box to a height of
1m in 2s. How much
power is used to lift the
box?
 Give:
 Formula:
 Solve:
Math Practice pg 415
 1.
 3.
 2.
Horsepower
 Horsepower

hp = 746 watts
 James Watts

Comparison of power
outputs of steam engines
vs
output of strong horse
Work and Machines
CH. 14.2
True
False
Statement
Machines make work easier, by changing
force, direction or distance
The force you exert on a machine is output
force
The final product of the machine is called
output force
Output work is always less than input force
due to friction
Both force input and force output are equal to
force x distance
True
False
Machines and Work
 Machine
 A device that changes force
 Make work easier by
Changing size of force
 Direction of force
 Distance over which force acts

Machines and Work
 Increasing Force


Small force over a large
distance = large force over
a short distance
Ex-jack
 Increasing Distance

Decrease applied force by
increasing the distance in
which the force is exerted
 Changing Direction

Ex-oar
Work Input
 Input force
force you exert on
machine
 Input distance
distance of input force
 Work Input
input force x input
distance
 Friction makes work
done by a machine less
than the work done on
the machine
Work Output
 Output force
force exerted by the
machine
 Output distance
distance of output force
 Work Output
output force x output
distance
Mechanical Advantage and
Efficiency
CH. 14.3
True
False
Statement
Mechanical advantage is the # of times a
machine increases output force
IMA is the ideal mechanical advantage, which
is only possibly without friction
AMA is the actual mechanical advantage,
which is output force/input force
Efficiency of a machine is the input work that
becomes output work
Efficiency can never equal 100%
True
False
Mechanical Advantage
 The # of times that a machine increases an input
force
 Ex: Nut cracker
 At pivot- 7 times your input force
 At middle- 3 times your input force
Mechanical Advantage
Actual
Ideal
 IMA is the mechanical
•AMA is the actual
forces acting on a
machine
advantage in the
absence of friction
 Actual MA is always
less than the IMA due
to friction
Calculating IMA
 IMA = Input Distance
 A woman drives her car
Output Distance
No SI Unit
onto a ramp for repairs.
She drives 1.8m along
the ramp to raise the car
0.3m. What is the IMA?
 Given:
 Formula:
 Solve:
Math Practice pg 425
 1.
 3.
 2.
Efficiency
 The % of work input that
becomes work output
 Due to friction, it is
always less than 100%
 Efficiency= Work Output
Work Input
X 100%
 Reduce friction = more
efficiency
Simple Machines
CH 14.4
True
False
Statement
Compound machines contain 2 or more of the
6 simple machines
There are 4 classes of levers, that depend
where the fulcrum is located
A thin wedge has a bigger IMA than a thick
wedge
A wheel and axle, is composed of 1 wheel, or
disk
An inclined plane IMA is the height/ the
distance
True
False
Simple Machines
 6 Simple Machines
Lever
 A ridged bar, free to
move around a fixed
point
 Fixed point moves
around a fulcrum
 IMA = input arm/output
arm
 1st Class

MA = 1, < 1, > 1
 2nd Class

MA = > 1
 3rd Class

MA = < 1
Name the Lever
Wheel and Axle
 2 disks with different radii
 IMA = radius of input force/ radius of output force
 MA = > 1
Inclined Plane
 Slanted surface along which a force moves an object
to difference elevation
 IMA = distance of inclined plane/ change in height
Wedge
 V shape, with 2 inclined
planes sloped into each
other
 MA = > 1
 Thin wedge of a given
length has a greater IMA
than a thick wedge of the
same length
Screw
 Inclined plane wrapped
around a cylinder
 Closer threads have more
IMA than far apart
threads
Pulley
 Rope that fits into a
groove in a wheel
 IMA = # of rope sections
supporting the load
being lifted
 Fixed Pulley


Rotate in place
MA = 1
 Movable Pulley

Attached to the object
being moved
 Pulley System

Mix of fixed and movable
Name the Pulley
Compound Machines
 Combination of 2 or more simple machines working
together
 Scissors

Wedge, and lever
Name the simple Machines
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