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.
b.
c.
velocity force 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.
4 2 0.25 0.5
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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 d. horizontal g. diagonal j. up b. none e. horizontal h. horizontal k. horizontal c. no f. yes i. yes l. no
Calculating Power
Section 14.1
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Calculating Power
Section 14.1
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Calculating Power
Section 14.1
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Calculating Power
Section 14.1
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Interest Grabber
Section 14.2
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
2.
scissors
4.
5.
desk ice pick
3.
chair
6.
bottle opener
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Reading Strategy
Section 14.2
Summarizing
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a. Decreases electrons c. Decreases b. Increases 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.
Forces and Work
Figure 7 Go to section
Forces and Work
Figure 7 Go to section
Forces and Work
Figure 7 Go to section
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
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a. The number of times a machine increases force b. Actual mechanical advantage c. Ratio of output force to input force d. Ideal mechanical advantage e. The mechanical advantage of a machine if there were no friction f.
Efficiency g. Percentage of work input that becomes work output
Calculating IMA
Section 14.3
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Calculating IMA
Section 14.3
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Calculating IMA
Section 14.3
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Calculating IMA
Section 14.3
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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
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a. less than 1 to greater than 1 b. between the input force and the output force c. seesaw, scissors, tongs
Three Classes of Levers Figure 13 Go to section
Three Classes of Levers Figure 13 Go to section
Three Classes of Levers Figure 13 Go to section
Three Classes of Levers Figure 13 Go to section
Three Classes of Levers Figure 13 Go to section
Three Classes of Levers Figure 13 Go to section
Three Classes of Levers Figure 13 Go to section
Three Classes of Levers Figure 13 Go to section
Three Classes of Levers Figure 13 Go to section
Three Classes of Pulleys Figure 19 Go to section
Three Classes of Pulleys Figure 19 Go to section
Three Classes of Pulleys Figure 19 Go to section
Three Classes of Pulleys Figure 19 Go to section
Three Classes of Pulleys Figure 19 Go to section
Three Classes of Pulleys Figure 19 Go to section
Three Classes of Pulleys Figure 19 Go to section
Three Classes of Pulleys Figure 19 Go to section
Three Classes of Pulleys Figure 19 Go to section
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.
b.
c.
velocity force 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
(continued)
Chapter 14 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
(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? 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
Answers Section 14.1
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
Answers Section 14.2
1.
2.
3.
4.
5.
6.
Doorknob A doorknob is a machine. The doorknob turns a bolt and allows the door to be opened.
scissors Scissors are a machine. Pressing the scissor handles together causes the scissor blades to slice through material.
chair The chair does not make work easier to do and is not a machine.
desk The desk does not make work easier to do and is not a machine.
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.
bottle opener A bottle opener is a machine. A botle opener makes it easier to pry the lid off a bottle.
Interest Grabber
Answers Section 14.3
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
Answers Section 14.4
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.
Go Online
Chapter 14
Data sharing Self-grading assessment For links on work, go to www.SciLinks.org
Web Code as follows: ccn-2141.
and enter the For links on machines, go to www.SciLinks.org
enter the Web Code as follows: ccn-2142.
and 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.