Activity 1.2.5 Mechanical System Efficiency
Introduction
Energy cannot be created or destroyed, but energy can
be converted from one form to another. By design, an
engineer creates an energy conversion system to
change an input energy form into a desired output
energy form. However, within a conversion system,
input energy can be changed into less desirable forms
of energy. Less desirable forms of energy conversion
can occur due to resistance and friction, resulting in
thermo energy conversion. Engineers strive to decrease
undesirable energy conversions within a system, or
energy losses, by planning with system efficiency in
mind. Efficiency is the ratio of desired output energy
compared to input energy.
Efficiency(%) =
Pout
 100
Pin
A common form of energy conversion today occurs
through electromagnetic induction. Electromagnetic
induction transfers mechanical energy into electrical
energy. The electrical energy is then transmitted to
industries and homes to be used in a variety of ways,
many of which include conversion back to mechanical
energy.
Equipment

Calculator
Procedure
In this activity you will investigate an energy conversion system designed to change
electrical energy into mechanical energy. Given ATV (All-Terrain Vehicle) winch
data, you will determine the efficiency of the system under various loads. Remember
units and precision when recording data.
© 2012 Project Lead The Way, Inc.
POE Activity 1.2.5 Mechanical System Efficiency ATV – Page 1
ATV Winch Data
ATV winches pull a horizontal load during testing. The winch pulls a weight where
the friction produces a force which is measured as tension in the cable. The
following data can be used to compare electrical input to mechanical output to
determine system efficiency.
Force
0
7000 N
11000 N
Distance
24 m
24 m
24 m
Time
180 s
360 s
720 s
Current
15 A
100 A
160 A
Volts
12 V
12 V
12 V
Work involves the amount of force (F) exerted over a specific distance (d). Note
that work is not related to time. For example running up a flight of stairs in four
seconds requires a different level of exertion than if you walk up a flight of stairs in
thirty seconds. You will feel differently in each scenario even though you did the
same amount of work. Use the following formula to determine how many joules (J)
of work it took to lift the weight in the system. As you carry your units through to the
solution, change the final answer from N∙m to J.
1. Determine the work done by the winch system for each test.
Formula
Substitute / Solve
Final Answer (0)
0*24=0
W = F∙d
7000*24
11000*24
0.1
168000J
264000J
Power involves time, force, and distance. In the previous example, the same
amount of work was done regardless of time. To climb the stairs more quickly, a
person needs more power. Use the formula below to calculate the output power of
the system in watts (W). As you carry your units through to the solution, change the
final answer from J/s to W.
1. Determine the output power of the system for each test. Your final answer will be
in watts.
Formula
Substitute / Solve
Final Answer (0.0)
© 2012 Project Lead The Way, Inc.
POE Activity 1.2.5 Mechanical System Efficiency ATV – Page 2
0/180
Pout =
Wout
t
0W
168000/360
264000/720
466.66W
366.66W
2. To calculate power of an electrical system, multiply the current and voltage.
Substitute and solve to discover how many watts were put into your system. You
do not need to show the relationship of units to solve the problem, but be sure to
label your final answer as watts.
Formula
Substitute / Solve
Pin = IV
Final Answer(0)
15*12
180W
100*12
1200W
160*12
1920W
3. In order to compare the energy input versus the output, the efficiency of the
system must be determined. Use the given formula to calculate efficiency.
Formula
Substitute / Solve
Final Answer (0.0)
0*180*100
0%
466.66/1200*100
38.88%
P
Efficiency(%) = out  100
Pin
© 2012 Project Lead The Way, Inc.
POE Activity 1.2.5 Mechanical System Efficiency ATV – Page 3
366.66/1920*100
19.09%
Conclusion
1. Which scenario is most efficient? What factors make one scenario more efficient
than another?
The second scenario. The input input power was less in comparisons to the output
than the other ones.
2. List and describe three factors that reduce the efficiency of this winch system.
Frcition with the ground
Friction in the winch
The ratio of input to output power
3. Describe at least one strategy for making this system more efficient.
Gear ratio to the motor to increase torque, allowing for less input power.
4. Explain at least two reasons why automotive engineers are concerned with
improving vehicle efficiency.
Better MPG’s can help to sell the car because consumer don’t want to pay lots for
gas.
If the effcienecy is not good enough the friction can generate heat, making it less
efficient.
© 2012 Project Lead The Way, Inc.
POE Activity 1.2.5 Mechanical System Efficiency ATV – Page 4