Transcript Prentice Hall Presentation Pro

Pretest
Chapter 14
1. According to Newton’s first law, if no net force acts on an object,
the object continues in motion with constant ________________.
a. velocity
b. force
c. acceleration
2. A horizontal force on an object can be broken down into these
components: 5 N north and 5 N east. If no other forces act on
the object, in what direction will the object move?
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Pretest (continued)
Chapter 14
3. Newton’s second law states that the net force acting on an object
equals the product of what two variables?
4. A machine produces an output force of 12.3 N when an input of
8.6 N is applied. What is the ratio of the machine’s output force
to its input force?
5. A person exerts 22 N on a box. If a frictional force of 3 N opposes
this force, what is the net force acting on the box?
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Pretest (continued)
Chapter 14
6. A machine has an output force of 57.3 N when a force of
32.6 N is used to operate the machine. What is the
percentage increase of the force?
7. A small wheel has a radius of 32 cm, and a large wheel has a
diameter of 128 cm. What is the ratio of the diameters of the
large wheel to the small wheel?
a.
b.
c.
d.
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4
2
0.25
0.5
Interest Grabber
Section 14.1
Work
Work is the product of force and distance. Work is done when a
force acts on an object in the direction the object moves. If a
force acts on an object but the object does not move, no work is
done.
1. A man pushes a grocery cart at constant speed from one
end of an aisle to the other. Identify the force, the
distance, and the work.
2. Describe two examples of work you do on a typical day.
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Reading Strategy
Section 14.1
Relating Text and Visuals
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a. up
b. none
c. no
d. horizontal
e. horizontal
f. yes
g. diagonal
h. horizontal
i. yes
j. up
k. horizontal
l. no
Calculating Power
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Section 14.1
Calculating Power
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Section 14.1
Calculating Power
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Section 14.1
Calculating Power
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Section 14.1
Section 14.2
Interest Grabber
What Is a Machine?
Look around you. Do you see any machines? Some
machines, like a lawn mower or a washing machine, are
complicated devices with many parts. Other machines are
very simple. You can tell a device is a machine if it makes
work easier to do.
Identify the machines in the following list of items. If the item
is a machine, describe how it makes work easier to do.
1. doorknob
4. desk
2. scissors
5. ice pick
3. chair
6. bottle opener
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Section 14.2
Reading Strategy
Summarizing
a. Decreases electrons
b. Increases
c. Decreases
d. Increases
e. Increase
f. Decreases
g. Machines can make work easier by changing the
size of the force or the direction of the force.
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Forces and Work
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Figure 7
Forces and Work
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Figure 7
Forces and Work
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Figure 7
Interest Grabber
Section 14.3
How Does Input Force Location Affect a Machine?
A nutcracker is a machine used to make cracking nuts easier.
As shown below, use a nutcracker to crack three nuts, each
time squeezing the nutcracker’s handles at a different location.
1. Applying force at which handle
location resulted in the
nutcracker cracking the nuts
the most easily?
2. How does the distance from
the nutcracker’s pivot point
to the point where the force is
applied affect the nutcracker’s
ability to crack nuts?
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Reading Strategy
Section 14.3
Building Vocabulary
a.
b.
c.
d.
e.
f.
g.
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The number of times a machine increases force
Actual mechanical advantage
Ratio of output force to input force
Ideal mechanical advantage
The mechanical advantage of a machine if there were no friction
Efficiency
Percentage of work input that becomes work output
Calculating IMA
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Section 14.3
Calculating IMA
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Section 14.3
Calculating IMA
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Section 14.3
Calculating IMA
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Section 14.3
Interest Grabber
Section 14.4
The Wheel and Axle
The wheel and axle is a simple machine that you probably see
everyday. It uses two discs or cylinders, each one with a different
radius. Look at the examples below. Can you identify each wheel
and axle?
1. What part of each
device is the wheel?
2. What part of each device
is the axle?
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Reading Strategy
Section 14.4
Summarizing
a. less than 1 to greater than 1
b. between the input force and the output force
c. seesaw, scissors, tongs
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Three Classes of Levers
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Figure 13
Three Classes of Levers
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Figure 13
Three Classes of Levers
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Figure 13
Three Classes of Levers
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Figure 13
Three Classes of Levers
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Figure 13
Three Classes of Levers
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Figure 13
Three Classes of Levers
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Figure 13
Three Classes of Levers
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Figure 13
Three Classes of Levers
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Figure 13
Three Classes of Pulleys
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Figure 19
Three Classes of Pulleys
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Figure 19
Three Classes of Pulleys
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Figure 19
Three Classes of Pulleys
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Figure 19
Three Classes of Pulleys
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Figure 19
Three Classes of Pulleys
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Figure 19
Three Classes of Pulleys
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Figure 19
Three Classes of Pulleys
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Figure 19
Three Classes of Pulleys
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Figure 19
Pretest Answers
Chapter 14
1. According to Newton’s first law, if no net force acts on an
object, the object continues in motion with constant
________________.
a. velocity
b. force
c. acceleration
2. A horizontal force on an object can be broken down into these
components: 5 N north and 5 N east. If no other forces act on
the object, in what direction will the object move?
northeast
Click the mouse button to display the answers.
Pretest Answers
Chapter 14
(continued)
3. Newton’s second law states that the net force acting on an
object equals the product of what two variables?
mass and acceleration
4. A machine produces an output force of 12.3 N when an input
of 8.6 N is applied. What is the ratio of the machine’s output
force to its input force?
1.4
5. A person exerts 22 N on a box. If a frictional force of 3 N
opposes this force, what is the net force acting on the box?
19 N
Click the mouse button to display the answers.
Pretest Answers
Chapter 14
(continued)
6. A machine has an output force of 57.3 N when a force of
32.6 N is used to operate the machine. What is the
percentage increase of the force?
176%
7. A small wheel has a radius of 32 cm, and a large wheel has a
diameter of 128 cm. What is the ratio of the diameters of the
large wheel to the small wheel?
a.
b.
c.
d.
4
2
0.25
0.5
Click the mouse button to display the answers.
Interest Grabber
Section 14.1
Answers
1. A man pushes a grocery cart at constant speed from one end
of an aisle to the other. Identify the force, the distance, and
the work.
The man supplies the force by pushing on the cart. The length
of the aisle is the distance. The work done is the product of
the force and the distance.
2. Describe two examples of work you do on a typical day.
Answers will vary. Sample answers: lifting a heavy school
bag; pushing or pulling a door open. Make sure students
correctly identify the force, distance, and work done.
Interest Grabber
Section 14.2
Answers
1. Doorknob
A doorknob is a machine. The doorknob turns a bolt and allows the door to be
opened.
2. scissors
Scissors are a machine. Pressing the scissor handles together causes the
scissor blades to slice through material.
3. chair
The chair does not make work easier to do and is not a machine.
4. desk
The desk does not make work easier to do and is not a machine.
5. ice pick
An ice pick is a machine. When thrust into a block of ice, the wedge-like tip of
an ice pick exerts forces that break the ice block apart.
6. bottle opener
A bottle opener is a machine. A botle opener makes it easier
to pry the lid off a bottle.
Interest Grabber
Section 14.3
Answers
1. Applying force at which handle location resulted in the
nutcracker cracking the nuts the most easily?
The nutcracker worked best when force was applied at
location 1.
2. How does the distance from the nutcracker’s pivot point
to the point where the force is applied affect the
nutcracker’s ability to crack nuts?
The greater the distance between the pivot and the
force, the better the nutcracker was at breaking nuts.
Interest Grabber
Section 14.4
Answers
1. What part of each device is the wheel?
A. The round knob is the wheel.
B. The outer part of the handle is the wheel.
C. The handle of the screwdriver is the wheel.
2. What part of each device is the axle?
A. The cylinder between the knob and the door is
the axle.
B. The cylinder from the handle to the sharpener is
the axle.
C. The shaft of the screwdriver is the axle.
Chapter 14
Go Online
Data sharing
Self-grading assessment
For links on work, go to www.SciLinks.org and enter the
Web Code as follows: ccn-2141.
For links on machines, go to www.SciLinks.org and
enter the Web Code as follows: ccn-2142.
For links on mechanical advantage, go to
www.SciLinks.org and enter the Web Code as follows:
ccn-2143.
For links on simple machines, go to www.SciLinks.org
and enter the Web Code as follows: ccn-2144.