HIGH SCHOOL SCIENCE
Physical
Science 4:
Simple
Machines
WILLMAR PUBLIC SCHOOL
2013-2014 EDITION
C HAPTER 4
Simple
Machines
In this chapter you will:
1. Describe the conditions that must exist for a force to
do work on an object.
2. Describe power.
3. Describe what a machine is and how it makes easier
to do work.
4. Relate the work input to a machine to the work output of the machine.
5. Explain why efficiency of a machine is always less
than 100%.
6. Name, describe, and give an example of each of the
six types of simple machines.
7. Describe how to determine the machine advantage of
each type of simple machine.
8. Define and identify compound machines.
S ECTION 4.1
Work & Power
L OREM
O
BJECTIVES
I PSUM
:
1. Lorem
Describe
ipsum
the connection
dolor sit amet
that must exist for a
force to do work on an object.
2. Consectetur adipisicing elit, sed do eiusmod
2. Describe
tempor incididunt
power. ut labore et dolore magna
aliqua.
3. Ut enim ad minim veniam, quis exercitation
Vocabulary:
ullamco laboris nisi ut aliquip ex commodo
work
consequat.
joule
4. Duis aute irure dolor in in voluptate velit esse
cillum dolore eu fugiat nulla pariatur.
power
watt
horsepower
You probably do many kinds of work. You may do work for
school. You may do work around your house, such as mowing
the lawn. You may work at a job. But these things are not
what scientists call work. For scientists, work has a special
meaning.
In science, work is the product of force and distance. Work is
the use of force to move an object. Work is only done when
there is movement. Work is done when a force acts on an object in the direction the object moves. For a force to do work
on an object, some of the force must act in the same direction
as the object moves. If there is no movement, no work is
done.
If you pushed as hard as you could against a heavy desk and
the desk did not move, you would not be doing work. But carrying a box is not work. When you carry a box, ou are using
force to keep the box from falling. The force is an upward
force. But the box is moving forward as you walk. The force
and the motion are not in the same direction. So no work is
being done.
Any part of a force that does not act in the direction of motion
does no work on an object.
Work = Force x Distance
The product of force and distance results in the units of
newton-meters, also known as joules. The joule (J) is the unit
of work.
2
Power is the rate of doing work. Doing work at a faster rate
requires more power.
To increase power, you can increase the amount of work done
in a given time, or you can do a given amount of work in less
time.
Power = Work / Time
The SI unit of power is the watt (W), which is equal to one
joule per second. Power has another common unit of power,
the horsepower. One horsepower (hp) is equal to about 746
watts.
Section Review:
1. When does a force do work?
2.If there is no movement, has work been done?
3. What is the equation for work?
4.What is the unit for work?
5. What is the equation for power?
6.What is the unit for power?
7. How are work and power related?
3
S ECTION 4.2
It is easier to pull a large rock in a wagon than to push it on
the ground. It is easier to tighten a nut with a wrench than
with your fingers. It is easier to raise a car with a jack than to
lift it yourself. A wagon, a wrench, and a jack are all machines.
Machines
O BJECTIVES :
1. Describe what a machine is and how it makes
workI PSUM
easier to do.
L OREM
2.
work
input
a machine to the work
1. Relate
Lorem the
ipsum
dolor
sitto
amet
output of the machine.
2. Consectetur adipisicing elit, sed do eiusmod
3. Compare
a machine’s
actual et
mechanical
tempor incididunt
ut labore
dolore magna
advantage
to its ideal mechanical advantage.
aliqua.
4.
the efficiency
a machine
is
3. Explain
Ut enim why
ad minim
veniam,of
quis
exercitation
always
thannisi
100%.
ullamcoless
laboris
ut aliquip ex commodo
consequat.
4.
Duis aute irure dolor in in voluptate velit esse
Vocabulary:
cillum dolore eu fugiat nulla pariatur.
machine
output distance
input force
work output
input distance
actual mechanical advantage
work input
ideal mechanical advantage
output force
efficiency
A machine is a device that changes a force. Machines make
work easier to do. The six types of simple machines are the
lever, the wheel and axle, the inclined plane, the wedge, the
screw, and the pulley. They change the size of a force needed,
the direction of a force, or the distance over which a force acts.
If a machine increases the distance over which you exert a
force, then it decreases the amount of force you need to exert.
Some machines decrease the applied force, but increase the
distance over which the force is exerted. Some machines
change the direction of the applied force.
Because of friction, the work done by a machine is always less
than the work done on the machine. The force you exert on a
machine is called the input force. The distance the input
force acts through is known as the input distance. The work
done by the input force acting through the input distance is
called the work input.
The force that is exerted by a machine is called the output
force. The distance the output force is exerted through is the
output distance. The work output of a machine is the output force multiplied by the output distance.
4
The mechanical advantage of a machine is the number of
times that the machine increases an input force. .
The actual mechanical advantage (AMA) equals the ratio
of the output force to the input force. The ideal mechanical
advantage (IMA) of a machine is the mechanical advantage
in the absence of friction. Because friction is always present,
the actual mechanical advantage of a machine is always less
than the ideal mechanical advantage.
Because friction reduces mechanical advantage, engineers often design machines that use low-friction materials and lubricants. The percentage of the work input that becomes work
output is the efficiency of a machine. Because there is always some friction, the efficiency of any machine is always
less than 100 percent.
Section Review:
1. What three things do machines change to make a task
easier to perform?
2.Why is work done by a machine always less than the
work done by you?
3. How does the actual mechanical advantage of a machine
compare to its ideal mechanical advantage?
4.What happens to the efficiency of a machine if you reduce
the friction?
5. Why can no machine be 100% efficient?
5
S ECTION 4.3
Simple Machines
O BJECTIVES :
1. Name, describe and give examples of each of
the six types of simple machines.
L OREM I PSUM
2. Describe how to determine the ideal
1. mechanical
Lorem ipsum
dolor sit of
amet
advantage
each type of simple
machine.
2. Consectetur adipisicing elit, sed do eiusmod
tempor incididunt ut labore et dolore magna
aliqua.
Vocabulary:
3. Ut enim ad minim veniam, quis exercitation
lever
wheel and axle
ullamco laboris nisi ut aliquip ex commodo
fulcrum
incline plane
consequat.
There are thousands of different kinds of machines. You use
machines every day. But did you know that all machines are
based on only six kinds of simple machines. The six types of
simple machines are the lever, the wheel and axle, the inclined
plane, the wedge, the screw, and the pulley.
A lever is a rigid bar that is free to move around a fixed point.
The fixed point the bar rotates around is the fulcrum. If you
push down on the end of one kind of lever, the other end
moves up. The input arm of a lever is the distance between
the input force and the fulcrum. The output arm is the distance between the output force and the fulcrum. Levers are
classified into three categories based on the locations of the input force, the output force, and the fulcrum.
input
armaute irure dolor
wedge
4. Duis
in in voluptate velit esse
cillum
nulla pariatur.
output
armdolore eu fugiat
screw
first-class lever
pulley
second-class lever
fixed pulley
third-class lever
moveable pulley
pulley system
6
The position of the fulcrum identifies a first-class lever—the
fulcrum of a first-class lever is always located between the
input force and the output force. In a second-class lever
the output force is located between the input force and the fulcrum. The input force of a third-class lever is located between the fulcrum and the output force.
To calculate the mechanical advantage of any lever, divide the
input arm by the output arm.
To calculate the mechanical advantage of the wheel and axle,
divide the radius (or diameter) where the input force is exerted by the radius (or diameter) where the output force is exerted.
An inclined plane is a slanted surface along which a force
moves an object to a different elevation. Moving an object up
an inclined plane requires less force than lifting it straight up,
at a cost of an increase in the distance moved.
A wheel and axle is a simple machine that consists of two
disks or cylinders, each one with a different radius. The outer
disk is the wheel and the inner cylinder is the axle.
A wheel and axle is a lever rotated completely in a circle
around the fulcrum. The axle is the smaller side, or output
arm, of the lever. The wheel is the larger side, or input arm, of
the lever.
The mechanical advantage of an inclined plane is the distance
along the inclined plane divided by its change in height.
7
A wedge is a V-shaped object. A wedge sides are two inclined
planes sloped toward each other.
A screw is an inclined plane wrapped around a cylinder. The
mechanical advantage on a screw is calculated by the number
of threads per centimeter. For two screws of the same length,
the one whose threads are closer together moves forward less
for each turn of the screw. Screws with threads that are closer
together have a greater mechanical advantage. A screw with
fewer threads per inch takes fewer turns to drive into a piece
of wood or other material. But the smaller mechanical advantage of the screw requires you to exert a greater input force in
order to drive it in.
A thin wedge of a given length has a greater ideal mechanical
advantage than a thick wedge of the same length. The mechanical advantage of a wedge is the distance along the wedge
divided by its change in width.
A pulley is a simple machine that consists of a rope that fits
into a groove in a wheel. Pulleys produce an output force that
is different in size, direction, or both, from that of the input
force.
The mechanical advantage of a pulley or pulley system is
equal to the number of rope sections supporting the load being lifted.
8
Section Review:
1. What defines a first-class lever?
2.What defines a second-class lever?
3. What defines a third-class lever?
4.How do you calculate mechanical advantage for lever?
5. How is a wheel and axle like a lever?
6.How do you calculate mechanical advantage for a wheel
and axle?
7. How does an incline plane make the effort on moving the
object easier?
A fixed pulley is a wheel attached in a fixed location. Fixed
pulleys are only able to rotate in place. A movable pulley is
attached to the object being moved rather than to a fixed location. By combining fixed and movable pulleys into a pulley
system, a large mechanical advantage can be achieved.
8.How do you calculate mechanical advantage for an
inclined plane?
9.How is a wedge like an inclined plane?
10.How do you calculate mechanical advantage for wedge?
11.How do you calculate the mechanical advantage for the
screw?
12.How do you calculate the mechanical advantage for the
pulley?
9
S ECTION 4.4
Compound Machines
Most of the machines you use every day are actually a combination of simple machines working together. A compound
machine is a combination of two or more simple machines
that operate together. Many familiar compound machines,
such as a car, a washing machine, or a clock, are combinations
of hundreds or thousands of simple machines.
Compound machines can make works even easier than simple
machines. In a compound machine, the force you pass on to
one simple machine is made larger and passed on to another
simple machine. In this way, the total force is made much
larger.
O BJECTIVES :
1. Describe and identify compound machines.
2. Describe how compound machines make work
easier.
Vocabulary:
compound machine
Compound machines are all around you. A scissors is a compound machine. It is simple two levers, with the fulcrum
where the pin is located. A can opener is a compound machine. The two handles are levers. The key you turn to open a
can is a wheel and axle. The blade that cuts into the can is a
wedge. A bicycle is another compound machine. Its wheels
are connected to axles. So they made a wheel and axle machine. The brake handles are levers.
A machine cannot make energy. But every machine needs energy. When you pedal a bicycle, you provide the energy.
Many machines use electric energy. All machines waste energy. Remember that friction is a foce that resists motion. Machines usually have moving parts that rub against each other.
Friction slows down the motion of the parts. So energy is
wasted. The work done by a machine is always less than the
work put into it.
10
Section Review:
1. How do compound machines make work easier than
simple machines?
2.How is the work done by a machine compare to the work
put into it?
3. Give an example of a compound machine and describe
the simple machine in it?
11