Date
Period
10
Enrichment
10
Name
Use with Chapter 10.
Name
Enrichment
8. Use your program to determine the effects on efficiency as the effort and resistance forces change.
Keep one force constant, and vary the other. How does an increase in effort force affect efficiency?
How does an increase in resistance force affect efficiency?
The Efficiency of a Pulley System
You have read that the ideal mechanical advantage, or IMA, of a machine is the ratio of the displacement of the effort to the displacement of the resistance. The equation used for this calculation is
IMA = de/dr. In a pulley system used to raise a heavy object, the effort displacement can be measured as
the length of rope that must be taken up as the resistance is moved, or the distance the rope is pulled.
The resistance displacement is the vertical distance the resistance is moved. In a pulley system, this will
be equal to the number of supporting ropes in the system. In a pulley system, there is really one rope
looped around several pulleys, but for the purpose of determining the IMA, each vertical segment that
supports the resistance counts as a supporting rope. The system shown consists of two fixed pulleys and
two movable pulleys. If you count the supporting ropes in this system, you will find that there are four
supporting ropes. The fifth rope segment is not supporting the resistance; it is an extension of the fourth
supporting segment. Thus, the IMA is 4.
9. What two forces in a pulley system tend to reduce efficiency?
Once you have counted the number of supporting ropes, you can use IMA to determine the efficiency of a pulley system. You can also program a computer to do the
calculations for you.
1. What is the equation used to calculate the actual mechanical advantage, MA, of
a pulley system?
2. What data do you need to calculate the mechanical advantage of a machine?
Copyright © by Glencoe/McGraw-Hill
Copyright © by Glencoe/McGraw-Hill
3. What equation is used to calculate the efficiency of a machine when the MA and
IMA are known?
4. In the space provided on page 20, draw a flowchart to calculate the efficiency of
a pulley system.
5. If you have access to a computer, follow your flowchart and write a computer program to calculate
the efficiency of a pulley system. Attach a printout of your program to this page.
6. When you run your program using laboratory data, would you expect the efficiency to be greater
than, less than, or equal to 100 percent? Explain your answer.
7. A pulley system with two supporting ropes uses a force of 131 N to lift a carton weighing 225 N.
Enter these data and run your program. What is the efficiency of this pulley system? Attach a printout of your results to this page.
Physics: Principles and Problems
Enrichment 19
20
Enrichment
Physics: Principles and Problems
10
Section 10.2:
10
Name
Study Guide
Machines
Name
Study Guide
14. A real machine has an efficiency equal to 100 percent.
In your textbook, read about mechanical advantage and efficiency.
For each of the statements below, write true or rewrite the italicized part to make the statement true.
15. The lower the efficiency of a machine, the greater the effort force needed to produce the same resistance force.
1. A machine makes doing a task easier.
2. A machine eases the load by changing either the magnitude or the direction of energy.
In your textbook, read about simple machines.
The numbers below correspond to the numbers in the diagram. For each number, write the letter of the matching
term from the right column. A term may be used more than once.
3. Work is the transfer of energy by mechanical means.
22
23
4. A machine cannot create energy.
20
21
24
16
5. The force that is exerted on a machine is the effort force.
17
25
18
7. When the mechanical advantage of a machine is greater than one, the machine decreases the effort
force.
12. The efficiency of a machine is the ratio of work output to work input.
Copyright © by Glencoe/McGraw-Hill
11. The IMA of most machines is fixed by their design.
Copyright © by Glencoe/McGraw-Hill
8. A real machine cannot have a mechanical advantage that is less than one.
10. If a machine transfers all of the energy applied to it, then the output work is less than the input
work.
16.
22.
17.
23.
18.
24.
58
Study Guide
Physics: Principles and Problems
a. axle
b. F e
Fr
c.
19.
25.
d. pivot point
20.
26.
21.
27.
e. r e
f. r r
g. wheel
Refer to the machine on the left in the diagram above. Circle the letter of the choice that best completes the statement or answers the question.
28. What is the value of the MA?
a. ⬎1
c. ⬍1
b. ⫽1
d. cannot be determined
29. What is the value of the IMA?
a. ⬎1
c. ⬍1
b. ⫽1
d. cannot be determined
30. To increase the IMA of the machine, you would
13. An ideal machine has an efficiency greater than 100 percent.
26
19
6. The product of the resistance force and the effort force is the mechanical advantage of the machine.
9. The ideal mechanical advantage of a machine can be used to calculate the distance the effort force
moves compared to the distance the resistance force moves.
27
.
a. increase r r
c. decrease r e
b. increase r e
d. decrease F r
Physics: Principles and Problems
Study Guide
59
10
Name
Date
Study Guide
10
In your textbook, read about compound machines.
Refer to the diagram below. For each term on the left, write the letter of the matching item.
Rear sprocket
Name
Study Guide
Use with Chapter 10.
Energy, Work, and Simple Machines
Front
sprocket
F by chain
Period
Vocabulary Review
Write the term that correctly completes each statement. Use each term once.
Fon chain
Fon pedal
Pedal
Rear wheel
Fon road
31. MA of pedal and front sprocket
rear sprocket radius
a. ᎐᎐᎐᎐᎐
wheel radius
32. IMA of pedal and front sprocket
Fon road
b. ᎏᎏ
Fby chain
33. MA of rear sprocket and rear wheel
kinetic energy
system
efficiency
machine
watt
effort force
mechanical advantage
work
energy
power
work-energy theorem
ideal mechanical advantage
resistance force
joule
simple machine
1.
The energy resulting from motion of an object is called
2.
The
states that the work done on an object is equal to the
object’s change in kinetic energy.
pedal radius
c. ᎐᎐᎐᎐᎐
front sprocket radius
3.
The force exerted on a machine is called the
4.
The ratio of the output work to the input work is a machine’s
34. IMA of rear sprocket and rear wheel
Fon road
d. ᎏᎏ
Fon pedal
5.
The SI unit of work is the
6.
35. MA of pedal and rear wheel
pedal radius
e. ᎐᎐᎐
wheel radius
The unit of power equal to 1 J of energy transferred in 1 s is the
.
f.
pedal radius
rear sprocket radius
᎐᎐᎐᎐᎐ ⫻ ᎐᎐᎐
front sprocket radius
wheel radius
Refer to the diagram above. Write the value ⬍1, ⫽1, or ⬎1 to complete the table below.
Table 1
Machine
MA Value
IMA Value
pedal and front sprocket
37.
38.
rear sprocket and rear wheel
39.
40.
pedal and rear wheel
41.
42.
Study Guide
Physics: Principles and Problems
Copyright © by Glencoe/McGraw-Hill
Fon chain
g. ᎐᎐᎐
Fon pedal
Copyright © by Glencoe/McGraw-Hill
36. IMA of pedal and rear wheel
60
compound machine
.
.
.
.
7.
A machine exerts
8.
The product of the applied force and the distance through which
the force is applied is
.
.
9.
The ability of an object to produce a change in itself or its surroundings is
.
10.
The rate of doing work is
11.
A device that changes the magnitude or direction of a force is a(n)
.
12.
The ratio of effort distance to resistance distance is a machine’s
.
13.
The ratio of resistance force to effort force is a machine’s
14.
A device that consists of two or more simple machines linked so
that the resistance force of one machine becomes the effort force of
the second machine is a(n)
.
15.
A defined group of objects is called a(n)
16.
A lever, pulley, wheel and axle, inclined plane, wedge, or screw is
a(n)
.
Physics: Principles and Problems
.
.
.
Study Guide
55