# Work, Power Simple Machines by Adela Sanders

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```									Work, Power &
Simple
Machines
Work
   Work- A force acting through a distance.

   The distance that the object moves must be in
the same direction as the force applied to the
object.
Weight
What force is
having to be
overcome by the                   Lifting Force
lifting force?

Weight!
Movement Distance
Work
   Work- A force acting through a distance.

   The distance that the object moves must be in
the same direction as the force applied to the
object.

What force is
having to be
overcome by the
pushing force?                         Pushing Force

Friction!                          Distance Moved
 Work is not done every time a force is applied.
 Work is done only when a force moves an object
in the same direction as the applied force.

Is the man doing
work when he
lifts the box?                            Lifting Force

Yes.

Is the man doing                         Movement
work when he                             Distance
holds the box?
Is the man doing
No!
work if he carries      No!
(But he IS applying a force)   the box?     (But he IS applying a force)
Work
Think about pushing on wall that does not
move. A force is applied but the wall has
not moved a distance.

Is work
done?

No!

But I did expend
energy applying
a force!
Calculating Work
 Work = force (N) x distance (m)
 W=FxD
 The unit for work is a Joule (J).
 If you lifted an object weighing 1N through a
distance of 1m, you did 1 Joule of work:

W = FD = 1N x 1m = 1 J

¼ of a pound.

Is a Joule of work…very much work?      No!
Calculating Work
 Ifyou lifted an object weighing 200 N through a
distance of 0.5m, how much work would you
do?

Work = force x distance = 200 N x 0.5m = 100 J.
Power
   Power is the rate at which work is done , or the
amount of work per unit of time.

Two men can move a lot of sand using shovels…

can do it in less time…

…because the front-end loader has more POWER.
Power
 Power  is the rate at which work is done ,
or the amount of work per unit of time.

 Power   = work / time or

 Power   = force x distance / time

Because work = force x distance
Power
 Theunit for power is watt (W). One watt is
equal to 1 joule per second (1 J/sec).

 Largequantities of power are measured in
kilowatts (kW).

 One                   1000
kilowatt equals _____ watts.
Machines : How do machines affect
 A machine is a device
work?
that makes work
easier.

   A machine is ANY
device that helps you
to do something.
Machines : How do machines affect
work?
 What   are other examples of machines?
Machines : How do machines affect
work?
Machines : How do machines affect work?
Machines : How do machines affect
work?
Machine Efficiency:
Input and Output
   There are always two types of work involved in
using a machine.

   Input work is the work that goes into the machine
(like turning a pencil sharpener).

   Output work is the work that comes out of the
machine (like the grinding of the pencil).

How hard was that??
Machine Efficiency: Input and Output
   The efficiency of a machine can be calculated:

Efficiency = (work output / work input) x 100

This is easy to remember…think about it…

If you put 100 Joules of work into a pencil sharpener,
but only got 80 Joules of work out, the pencil
sharpener is 80% efficient:

(80 Joules / 100 Joules) x 100 = 80% efficiency
 Machine  efficiency can never be greater
than or equal to 100% because the work
output can never be greater than the work
input.

 Inother words, there is no machine that
has a 100% efficiency!

Why not?
Think…it’s a force that opposes
motion…

Friction!
Friction makes every machine <100% efficient
Machine Efficiency

 The friction in a machine “wastes” energy
in the form of heat

 Machines   with the smallest amount of
friction are the most efficient.
Machine Efficiency
   The closer the work output is to work input, the
more efficient the machine.

Toyota hybrid
“concept car”
Many household
appliances have energy
guides that tell the
consumer how efficient
the appliance is. The
more efficient the
appliance the more
money the consumer
will save.
You can also look for
the “energy star” label
on more efficient
machines.
Machines
   Machines make work easier because they
change the size or the direction of the force put
into the machine.

More
force
Machines
   Most machines make work easier by
multiplying either force or distance.

Force!                Distance!

Which does which?
Machines
   What is multiplied, force or distance?

Force                     Distance

Force when “prying” the dirt free, distance when lifting
it up out of the hole or into a truck or wheelbarrow
Machine Is

 Besidesthe efficiency of a machine we also
can determine how helpful a machine is.
Machine Is
   What we mean by how helpful is how many times
the machine multiples the effort force to overcome
the resistance force
Effort Force

Resistance Force
Machine Is   ? Effort
Force

Resistance
Force   ?

Effort Force or
Resistance Force?
Effort
?   Force
Machine Is
 The number of times a machine multiplies
the effort force is called the mechanical

 Thistells you how much force is gained by
using the machine. The more times the
machine multiples the effort force, the
easier it is to do the job.
Quick quiz –open notes
 1. What is a machine?
 2. Describe relationship between friction
and the efficiency of a machine.
6 Kinds of Simple Machines

Inclined Plane   Wedge   Lever

Wheel & Axle     Screw   Pulley
Inclined Plane
 Inclinedplane: A ramp is an example of an
inclined plane. It is simply a flat slanted
surface. It has no moving parts.
Inclined Plane
 Aninclined plane decreases the size of
the effort force needed to move an object.
Wedge
 Wedge:    An inclined plane that moves.
 In a wedge, instead of an object moving
along the inclined plane, the inclined plane
itself moves to raise the object.
Wedge
A wedge is usually a piece of wood or
metal that is thinner at one end. A knife
and axe are two examples.
Wedge
 Wedge    : the longer and thinner a wedge
is, the less the effort force required to
overcome resistance. This also is true for
an inclined plane.
Wedge
 When  you sharpen a wedge, you are
decreasing the effort force that must be
applied in using it.
 A sharpened ax requires less force
because the edge is thinner
Wedge
A lock is another device that depends on
the principle of the wedge. The edges of
the key are a series of wedges.
Wedge
A zipper is also a device that depends on
the principle of a wedge.
Lever
 Lever : A lever is a rigid bar that is free to
pivot , or move about a fixed point. The
fixed point is called the fulcrum.
Lever
 When  a force is applied on a part of the
bar by pushing or pulling it, the lever
swings about the fulcrum and overcomes
a resistance force.
Levers
 Leversare divided into three groups, or
classes, depending on the location of the
fulcrum and the forces.
Levers
 Examples of first class levers are
crowbars, seesaw and pliers.
Levers
 The  fulcrum of a lever is not always
between the effort force and the resistance
force like the example of a crowbar.
Sometimes it is at the end of the lever.
 A wheelbarrow is a second class lever.
Levers
 Where is the effort, resistance, and
fulcrum?
 Because distance is decreased by the
wheelbarrow, force must be increased.
Levers
 In second class levers, you multiply force
but decrease distance.
 Also with second class levers, the
direction in which you lift is the same as
the direction in which the load moves.
 A 2nd class lever does not change the
direction of the force applied to it.
Levers
 Ina third class lever, the fulcrum or fixed
point, is at the end of the pole where you
are holding it like a fishing pole.
Levers
 The effort force is applied by your other
hand as you pull back on the pole. At the
top of the pole is the resistance force. In
this class, you need to move your effort
force only a short distance to make the
end of the pole move a greater distance.
Levers
A 3rd class lever, reduces the effort
required but multiplies the distance
through which the output force moves.
Wheel and Axle
A wheel and axle is a simple machine
made up of two circular objects of different
sizes. The wheel is the larger object. It
turns around a smaller object called the
axle.
Wheel and Axle
A  force applied to the wheel is multiplied
when it is transferred to the axle, which
travels a shorter distance than the wheel
Wheel and Axle
 The mechanical advantage depends on
the radius of the wheel and of the axle.
Wheel and Axle
 Examples  of wheels and axles are
bicycles, Ferris wheels, gears, wrenches,
door knobs, steering wheels, windmills
and screwdrivers.
Screw
 Screw  : A screw is inclined plane wrapped
around a central bar or cylinder to form a
spiral.
Screw
 A screw rotates and with each turn moves a
certain distance up or down. A screw multiplies
an effort force by acting through a long distance.
 The closer together the threads, or ridges, of a
screw, the longer the distance over which the
force is exerted and the more the force is
multiplied. Thus the mechanical advantage of a
screw increases when the threads are closer
together.
Screw
 Examples of a screw are the wood screw,
corkscrew, nut and bolt, faucets, jar lids,
and spark plugs.
Pulley
A  pulley is a rope, belt, or chain wrapped
around a grooved wheel.
 A pulley can function in two ways. It can
change the direction of a force or the
amount of force.
Pulley
A pulley that is attached to a structure is
called a fixed pulley. A fixed pulley does
not multiply an effort force it only changes
the direction of the effort force.
Pulley
 Pulleyscan be made to multiply the force
with which you pull on them. This is done
by attaching a pulley to the object you are
moving. This type of pulley is called a
moveable pulley.
Pulley
A greater mechanical advantage can be
obtained by combining fixed and movable
pulleys into a pulley system.
Compound Machines
A  compound machine is a combination of
two or more simple machines.
 Most of the machines you use everyday
are compound machines: cars, bicycles,
washing machine, VCR, blender,watches,
etc.
Compound Machines
 Simple or compound machines cannot
multiply work. You can get no more work
out of a machine than you put into it.
True or False (If false correct)
 1. Work equals force times time.
 2. The unit of work in the metric system is
the newton-meter or joule.
 3. Power is work divided by force.
 4. The unit for power is newton.
 5. A pulley is an inclined plane that moves.
 6. An ax is an example of a wheel and
axle.

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