Transcript MS Science

Chapter Introduction
Lesson 1
Work and
Power
Lesson 2
Using
Machines
Lesson 3
Simple
Machines
Chapter Wrap-Up
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How do machines make
doing work easier?
What do you think?
Before you begin, decide if you agree or
disagree with each of these statements.
As you view this presentation, see if you
change your mind about any of the
statements.
Do you agree or disagree?
1. Work is done when you push a book
across a table.
2. Doing work faster requires more power.
3. Machines always decrease the force
needed to do a job.
Do you agree or disagree?
4. A well-oiled, low-friction machine can
be 100 percent efficient.
5. A doorknob is a simple machine.
6. A loading ramp makes it easier to lift a
load.
Work and Power
• What must happen for work to be
done?
• How does doing work on an object
change its energy?
• How are work and power related?
Work and Power
• work
• power
What is work?
In science, work is the transfer of energy
that occurs when a force makes an
object move.
work
from Old English weorc,
means “activity”
What is work? (cont.)
• Work is important in science because it
is related to energy.
• A force that does not make an object
move does no work.
Calculating Work
• To calculate work, multiply the force
applied to the object by the distance the
object is moved by that force.
• The product of force and distance has
the unit newton·meter. The newton·
meter is also known as the joule (J).
Calculating Work (cont.)
How is work done?
The work done on an object depends on
the direction of the force applied and the
direction of the motion.
Hutchings Photography/Digital Light Source
When the force and the motion are in the
same direction, calculate work by
multiplying the force and the distance.
Hutchings Photography/Digital Light Source
When the applied force and the motion of
the object are NOT in the same direction,
the applied force
can be thought
of as being two
forces acting on
the object at the
same time.
Hutchings Photography/Digital Light Source
• When the applied force and the motion
of the object are NOT in the same
direction, only
the horizontal
part of the applied
force is used in
the work
equation.
• The vertical part
of the applied force
does no work on
the suitcase.
Hutchings Photography/Digital Light Source
The work done to lift
an object equals the
weight of the object
multiplied by the
distance it is lifted.
Hutchings Photography/Digital Light Source
Work and Energy
• Doing work on an object transfers
energy to the object.
• This helps scientists predict how an
object will act when forces are applied
to it.
• Work done when you lift an object also
increases the object’s energy.
Doing work on a tray transfers energy to
the tray. The added energy can be either
kinetic energy or potential energy.
Work and Energy (cont.)
How does doing work on an
object change its energy?
What is power?
•
Power is the rate at which work is
done.
•
You can also think of power as how fast
energy is transferred to an object.
What is power? (cont.)
power
Science Use the rate at which
work is done
Common Use the ability to
accomplish something or to
command or control other people
What is power? (cont.)
You can calculate power by dividing the
work done by the time needed to do the
work.
What is power? (cont.)
How are work and power related?
• Work is done on an
object when the object
moves in the direction
of the applied force.
• When work is done
on an object, energy
is transferred to the
object.
Hutchings Photography/Digital Light Source
• To increase power, work must be done
in less time.
Hutchings Photography/Digital Light Source
When you lift an object, what else
are you doing?
A. decreasing the object’s energy
B. increasing the object’s energy
C. making the object do work
D. receiving the object’s energy
Which is the rate at which work is
done?
A. energy
B. force
C. power
D. work
To calculate the work done lifting
an object, which is multiplied by
the weight of the object?
A. distance the object is lifted
B. energy used to lift the object
C. force applied to the object
D. power needed to lift the object
Do you agree or disagree?
1. Work is done when you push a book
across a table.
2. Doing work faster requires more power.
Using Machines
• What are three ways a machine can
make doing work easier?
• What is mechanical advantage?
• Why can’t the work done by a
machine be greater than the work
done on the machine?
Using Machines
• mechanical advantage
• efficiency
What is a machine?
• A machine is any device that makes
doing something easier.
• Some machines are simple and other
machines are more complex.
Gabe Palmer/Alamy
What is a machine? (cont.)
• Machines make tasks easier, but do not
decrease the amount of work required.
• A machine changes the way in which the
work is done.
Royalty-Free/CORBIS
S. Alden/PhotoLink/Getty Images
What is a machine? (cont.)
• The force you apply to a machine is the
input force.
• The machine
changes the
input force to
an output force.
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What is a machine? (cont.)
The amount of
input force
multiplied by the
distance over
which the input
force is applied is
the input work.
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What is a machine? (cont.)
Machines convert
input work to
output work by
applying an output
force on
something and
making it move.
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How do machines make work easier
to do?
A machine makes
work easier by
changing the size
of the force, the
distance the force
acts, or the
direction of a
force.
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How do machines make work easier
to do? (cont.)
When the output
force is greater
than the input
force, the output
force acts over a
shorter distance.
Steve Gorton/Dorling Kindersley/Getty Images
Machines make work easier in three ways:
When the output force acts over a longer
distance than the input force, the output
force is less than the input force.
Sean Justice/Getty Images
Machines make work easier in three ways:
Equal output and input forces act over
equal distances.
Machines make work easier in three ways:
How do machines make work easier
to do? (cont.)
In what three ways do
machines make doing
work easier?
What is mechanical advantage?
A machine’s mechanical advantage
is the ratio of a machine’s output force to
the applied input force.
What is mechanical advantage? (cont.)
The mechanical advantage tells you how
many times larger or smaller the output
force is than the input force.
mechanical
from Greek mechanikos,
means “machine”
What is mechanical advantage? (cont.)
• Mechanical advantage can be less than
1, equal to 1, or greater than 1.
• A mechanical advantage greater than
1 means the output force is greater than
the input force.
• The ideal mechanical advantage is the
mechanical advantage if no friction
existed.
What is mechanical advantage? (cont.)
What is mechanical
advantage?
What is efficiency?
• The output work done by a machine
never exceeds the input work of the
machine.
• Friction converts some of the input work
to thermal energy and this converted
energy cannot be used to do work.
What is efficiency? (cont.)
• The efficiency of a machine is the ratio
of the output work to the input work.
• Because output work is always less than
input work, a machine’s efficiency is
always less than 100 percent.
What is efficiency? (cont.)
Why can’t the work done by a
machine be greater than the
work done on the machine?
• A machine makes a task easier and
it can be simple or complex.
• The mechanical advantage of a
machine indicates
how it changes
an input force.
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• The efficiency of a machine is
increased when a lubricant coats
moving parts.
Which is the product of the output
force and the distance over which
the output force is applied?
A. machine
B. input work
C. output work
D. mechanical advantage
How can a machine NOT make
work easier?
A. change the direction of the input
force
B. decrease the input force
C. increase the amount of work done
D. increase the input force
Which refers to the ratio of a
machine’s output work to its input
work?
A. efficiency
B. input force
C. mechanical advantage
D. output force
Do you agree or disagree?
3. Machines always decrease the force
needed to do a job.
4. A well-oiled, low-friction machine can
be 100 percent efficient.
Simple Machines
• What is a simple machine?
• How is the ideal mechanical
advantage of simple machines
calculated?
• How are simple machines and
compound machines different?
Simple Machines
• simple machine
• inclined plane
• lever
• wedge
• fulcrum
• screw
• wheel and axle
• pulley
What is a simple machine?
• Six types of simple machines do work
using only one movement.
• lever
• wheel and axle
• inclined plane
• wedge
• screw
• pulley
What is a simple machine? (cont.)
Describe a simple machine.
Levers
• A lever is a simple
machine made up
of a bar that pivots,
or rotates, about a
fixed point.
• The point about
which a lever pivots
is called a fulcrum.
Steve Gorton/Dorling Kindersley/Getty Images
Levers (cont.)
• In a first-class lever,
the fulcrum is
between the input
force and the output
force.
• The direction of the input force is
opposite the direction of the output force.
Levers (cont.)
A finger tab on a beverage can is a firstclass lever.
Jupiterimages
Levers (cont.)
• A second-class lever
has the output force
between the input force
and the fulcrum.
• The output force and the input force act
in the same direction.
• A second-class lever makes the output
force greater than the input force.
Levers (cont.)
A wheel barrow is an example of a secondclass lever.
Digital Vision / Alamy
Levers (cont.)
• A third-class lever
has the input between
the output force and
the fulcrum.
• The output force is less than the input
force. Both the input force and the output
force act in the same direction.
Levers (cont.)
A rake is an example
of a third-class lever.
Doug Menuez/Getty Images
Levers (cont.)
The ideal mechanical advantage of a lever
equals the length of the input arm divided
by the length of the output arm.
Mechanical Advantage of Levers
Mechanical Advantage of Levers
Mechanical Advantage of Levers
Levers (cont.)
How is the ideal
mechanical advantage
of a lever calculated?
Levers (cont.)
The neck, foot, and arm are examples of
first-, second-, and third-class levers in the
human body.
Wheel and Axle
• A wheel and axle
is an axle attached
to the center of a
wheel and both rotate
together.
• For a wheel and axle,
the length of the input arm is
the radius of the wheel and the
length of the output arm is the
radius of the axle.
Don Tremain/Getty Images
Wheel and Axle (cont.)
A screwdriver is a wheel and axle.
The handle is the wheel and the shaft is
the axle.
Wheel and Axle (cont.)
Even though no machine is 100% efficient,
you can calculate the ideal mechanical
advantage of a wheel and axle.
Inclined Planes
• A ramp, or inclined plane, is a flat,
sloped surface.
• It takes less force to move an object
upward along an inclined plane than it
does to lift the object straight up.
Moving a sofa is easier using a ramp.
Using a ramp only requires a 100-N force
to move the 500-N sofa. Because of
friction, no ramp operates at its ideal
mechanical advantage.
Inclined Planes (cont.)
The ideal mechanical advantage of an
inclined plane equals its length divided by
its height.
Inclined Planes (cont.)
• The longer or less-sloped an inclined
plane is, the less force is needed to
move an object along its surface.
• A sloped surface that moves is called a
wedge.
• A wedge is really a type of inclined plane
with one or two sloping sides.
Inclined Planes (cont.)
• A screw is an inclined plane wrapped
around a cylinder.
• When you turn a screw, the screw
threads change the input force to an
output force and the output force pulls
the screw into the material.
Pulleys
A pulley is a simple machine that is a
grooved wheel with a rope or a cable
wrapped around it.
Pulleys (cont.)
A fixed pulley only changes
the direction of the force.
Pulleys (cont.)
Movable pulleys are
attached to the object being
lifted and decrease the
force needed to lift the
object.
Pulleys (cont.)
A pulley system is a
combination of fixed and
movable pulleys that work
together.
Pulleys (cont.)
The ideal mechanical advantage of a pulley
or a pulley system is equal to the number
of sections of rope
supporting the object.
What is a compound machine?
Two or more simple machines that operate
together form a compound machine.
How are simple machines and
compound machines different?
What is a compound machine? (cont.)
• A gear is a wheel and axle with teeth
around the wheel.
• Two or more
gears working
together form
a compound
machine.
Brand X Pictures
What is a compound machine? (cont.)
• When the teeth of two gears interlock,
turning one gear causes the other to
turn.
• Gears of
different sizes
turn at different
speeds.
CORBIS
What is a compound machine? (cont.)
• The efficiency of a compound machine
is calculated by multiplying the
efficiencies of each simple machine
together.
• Each simple machine decreases the
overall efficiency of the compound
machine.
• Six simple machines are the lever,
wheel and axle, inclined plane,
wedge, screw, and pulley.
• All levers rotate, or pivot, about the
fulcrum.
• The kind of wedge used to split logs
is a simple machine.
What are levers, wheels and
axles, inclined planes, wedges,
screws, and pulleys examples of?
A. complex machines
B. compound machines
C. idea machines
D. simple machines
Which uses less force to raise an
object compared to lifting the
object straight up?
A. fulcrum
B. inclined plane
C. screw
D. wheel
Which is a simple machine
consisting of a grooved wheel with
a rope or cable wrapped around it?
A. gear
B. pulley
C. screw
D. wedge
Do you agree or disagree?
5. A doorknob is a simple machine.
6. A loading ramp makes it easier to lift
a load.
Key Concept Summary
Interactive Concept Map
Chapter Review
Standardized Test Practice
A machine makes work
easier by changing the
size of the applied
force, changing the
distance over which
the applied force acts,
or changing the
direction of the applied
force.
Lesson 1: Work and Power
• For work to be done on an object, an applied force
must move the object in the direction of the force.
• When work is done on an object, the energy of the
object increases.
• Power is the rate at which work is done.
Hutchings Photography/Digital Light Source
Lesson 2: Using Machines
• A machine can make work easier in three
ways: changing the size of a force,
changing the distance the force acts,
or changing the direction of a force.
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• The mechanical advantage of a machine
is the ratio of the output force to the input force.
• Because of friction, the output work done by a machine
is always less than the input work to the machine.
• Friction between moving parts converts some of the
input work into thermal energy and decreases the
efficiency of the machine.
Lesson 3: Simple Machines
• A simple machine does work
using only one movement.
• The ideal mechanical
advantage of simple
machines is calculated using
simple formulas.
• A compound machine is made up of two or more
simple machines that operate together.
What two things must you know
to calculate work?
A. distance and length
B. force and distance
C. force and power
D. height and weight
What do you divide work by to
calculate power?
A. distance
B. force
C. time
D. weight
Which refers to the force you
apply to a machine to make it
work?
A. energy
B. input force
C. output force
D. power
What does a machine apply to an
object?
A. output power
B. output force
C. mechanical advantage
D. input force
What does a lever rotate around?
A. axle
B. fulcrum
C. screw
D. wedge
What is transferred when work is
done?
A. distance
B. energy
C. force
D. power
The work done on an object
depends on the direction of the
force applied and which of these?
A. power
B. force of the motion
C. distance of the motion
D. direction of the motion
What is the ratio of a machine’s
output force to its input force?
A. efficiency
B. equal output
C. mechanical advantage
D. output work
What is a simple machine made
of a bar that rotates about a fixed
point?
A. fulcrum
B. lever
C. wedge
D. wheel and axle
What term describes an inclined
plane wrapped around a cylinder?
A. wedge
B. screw
C. fulcrum
D. axle