Lesson 2
Using Machines
Predict three facts that will be discussed in Lesson 2 after reading the headings. Record your
predictions in your Science Journal.
Distinguish the functions of machines.
What is a machine?
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95
.
Machines Do
make a task easier
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96
.
Machines Do Not
decrease the amount of
work required to do a task
Organize details about input work and output work.
Input work (Win)
input force
×
distance machine moves in the
direction of the force
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Output work (Wout)
output force
How do machines make
work easier to do?
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96
×
distance part of the machine
moves in the direction of
the force
Cite 3 ways machines make work easier.
.
change the size
of a force
Ways machines
make work
easier
change the
distance over
which a force acts
change the
direction of a
force
Work and Simple Machines
29
Lesson 2 | Using Machines (continued)
Analyze ways in which machines make work easier.
Change
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97
Drawing:
.
Make the
output force
greater than
the input
force
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97
.
Make the
output
distance
greater than
the input
distance
97
.
Make the
direction of
the output
force
different
from the
direction of
the input
force
What is mechanical
advantage?
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98
Work and Simple Machines
Drawing:
Drawings in the
input column
should show a
shorter force arrow
and longer distance
relative to the
output column.
A smaller force over a
longer distance converts
to
a greater force over
a shorter distance
Drawing:
Drawing:
Drawings in the
input column
should show a
longer force arrow
and shorter
distance relative to
the output column.
A greater force over a
shorter distance
converts to
a smaller force over
a longer distance
Drawing:
Drawing:
Drawings in the
input column
should show a
force arrow and
distance of equal
length to those in
the output column.
Direction of output
force should differ
from direction of
input force.
Force and distance
remain the same, but
the direction of the
output force differs
from that of the
input force
Define mechanical advantage.
the ratio of the output force applied to the input force
.
applied
30
Output Work
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
I found this on page
Input Work
Lesson 2 | Using Machines (continued)
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98
.
Identify components of the mechanical advantage
equation. Include the units for the F variables.
output force
(in newtons)
mechanical
advantage
MA =
Fout
Fin
input force
(in newtons)
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98
.
Complete the statement about mechanical advantage. Use the
symbol > or <.
MA > 1
What is efficiency?
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
I found this on page
99
means
that
output
force
>
input
force
Define efficiency, and complete the efficiency equation.
.
Efficiency: the ratio of output work to input work
Wout
efficiency =
×
100%
Win
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99
.
Explain the effect of friction on the efficiency of a machine.
Friction converts some of the input work to thermal energy.
The converted energy cannot be used to do work, so the
resulting output work of a machine is less than the original
input work.
Explain why a machine that has an output force less than its input force
can still be useful. Give an example.
Accept all reasonable responses. Sample answer: A rake has an output force less
than its input force. However, its output distance is far greater than its input distance,
which is why it is useful for gathering leaves.
Work and Simple Machines
31