Kinetic and Potential Energy (Lesson Plan)
(An Introduction to the Physics of Motion through the use of Milk Carton Cars)
Suggested Grade Level
8-10
Standard Statements
3.1.4 E
Recognize change in natural and physical systems.
3.2.4 C
Recognize and use the elements of scientific inquiry to solve problems.
3.4.4 B
Know basic energy types, sources, and conversions.
3.4.4 C
Observe and describe different types of force and motion.
3.6.4 C
Know physical technologies of structural design, analysis and engineering, finance,
production, marketing, research and design.
3.7.4 B
Select appropriate instruments to study materials.
Content Objectives
Students will know that
1. Potential energy represents the amount of energy stored in an object due to its height above
ground.
2. Kinetic energy is the energy associated with the movement of an object.
3. The potential energy of an object is equal to the product of its mass, its height above the
ground, and the acceleration due to gravity.
4. The kinetic energy of an object is equal to the product of its mass, the square of its velocity,
and a factor of ½.
5. The potential energy of an object increases as its mass increases and as its height above
ground increases.
6. The kinetic energy of an object increases as its mass increases and as its velocity increases.
7. The acceleration of an object along a ramp is equal to the acceleration due to gravity
multiplied by the ratio of the ramp, where the ratio of the ramp is equal to the ramp height
divided by the length of the ramp.
8. The final velocity of an object can be calculated given its initial velocity, its acceleration
over the distance of interest, and the time it took the object to traverse that distance.
Process Objectives
Students will be able to
1. Calculate the acceleration of a milk carton car along a ramp given the height and length of
the ramp.
2. Calculate the final velocity of a milk carton car at the bottom of a ramp given that it started
from rest.
3. Calculate the potential energy of a milk carton car at the top of a ramp given the ramp height
and the total mass of the milk carton car.
4. Calculate the kinetic energy of a milk carton car at the bottom of a ramp given the total mass
of the car and its final velocity at the bottom of the ramp.
5. Calculate an average time and average distance given three times and three distances.
Assessment Strategies
1. Evaluation of completed student handouts.
2. Group discussion of the questions in Part 4.
Kinetic and Potential Energy
Lesson Plan
1
Materials
Per group:
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1 milk carton (8-oz. or larger)
2 axles – 4 in. long; 3/8 in. diameter plastic or wooden dowel rod
1 drinking straw cut in half (each half approx. 3.75 inches long)
4 cardboard wheels, 1.5 in. diameter
One 3-oz. paper cup
Calculator
Scissors
Rulers
Tape measure
Stop watch
Tape
Wooden or foam board (or any type of flat surface suitable for a ramp)
30 washers (3/8 in.)
Books for stacking
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Balances
Per class:
Procedures
Part 1
(2, 45-min class periods)
1. Distribute materials to each group.
2. Have students build the milk carton car by following the directions provided in the
Additional Resources section of their student handout.
3. Have students build the test ramp as illustrated the student handout.
4. Go over Figure 2 with the students to make sure they understand what they will be
measuring as their car rolls down the ramp.
5. Discuss with the class why it is often important to do several trials during experimentation.
Draw the students’ attention to Table 1 in their handout and help them understand where
they will be recording their measurements.
6. Have the students roll their car down the ramp three times each for the three different ramp
heights 0.1 m, 0.2 m, and 0.3 m. For each trial, have the students measure the time it takes
their car to roll down the ramp and how far the car rolls once it reaches the bottom of the
ramp. Make sure the students measure the distances in meters and not centimeters. Have
them record all of their measurements in Table 1.
7. Instruct students to calculate an average time and distance traveled for each ramp height and
record it in the appropriate space in Table 1.
8. Have students mass their milk carton cars and then record it in Box #1 in their handout.
Make sure students understand that the mass needs to be in kilograms. Point out the
conversion in their handout that there are 1000g in 1 kg.
9. Have the students read about potential energy in their handout and then have them explain
what it means in their own words. Ask the students to predict whether or not their car will
have the same or different potential energy when the height of the ramp changes.
10. Have the students calculate the potential energies of their cars at the three different ramp
heights. Instruct the students to record their calculated potential energies in Table 1.
Kinetic and Potential Energy
Lesson Plan
2
Part 2
(1, 45-min class period)
1. Have the students read about kinetic energy in their handout and then have them explain
what it means in their own words.
2. Help the students understand that because kinetic energy is the energy of motion, an object
at rest does not have kinetic energy. For their milk carton cars, this means that vinitial=0.
3. Tell the students that in order to find the kinetic energy of their milk carton cars at the
bottom of the ramp, they need the velocity of their cars when it reaches that point. Allow
the students to work through the series of questions in their handout that walks them through
finding the velocity (vfinal).
4. If needed, clarify the purpose of using the ramp ratio (R) and what it means. Instead of
using angles and trigonometry in this activity to find acceleration, the ramp ratio is used.
Help the students understand Figures 3 and 4 and how the ramp ratio is directly related to
the angle the ramp makes with the ground.
5. Since it will be easy for students to get bogged down in the calculations involved in this
activity, remind them that the reason for finding the ramp ratio is to calculate the
acceleration, which is needed to find the velocity of the cars. Once the velocity is known,
the kinetic energy of the cars can be found.
6. Have students calculate R (ramp ratio) and the acceleration for each ramp height. These
values should be recorded in Table 2.
7. Instruct the students to complete Table 3, which asks for vfinal for each height. Students
should then calculate the kinetic energies of their cars to complete Table 4.
Part 3
(1, 45-min class period)
1. Have the students make a prediction about what they think will happen when they add
weights to their car. They should record this prediction in their handout.
2. Have the students follow the directions in their handout to find out what happens as weight
is added to their cars.
3. Help the students to understand that when they add weights to their car, they are
manipulating the mass term in the kinetic and potential energy equations.
4. The students can fill in the first row of Table 5 given their previous data.
5. Have the students mass one of their washers and then calculate the total mass of their car
with the 6 and 12 washers.
6. Have students calculate vfinal and KE of the car for each of the masses.
Part 4
(Variable)
1. Assign the questions in Part as a small group discussion activity or as a homework
assignment.
2. Discuss the questions as a class.
Kinetic and Potential Energy
Lesson Plan
3
Kinetic and Potential Energy (Teacher Notes)
(An Introduction to the Physics of Motion through the use of Milk Carton Cars)
General Lesson Notes
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Units in this activity. Please make sure that the students measure all distances in meters (and
not centimeters) and convert all measured masses in grams to kilograms.
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Variables, constants, and equations.
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distance (d) has units of meters
time (t) has units of seconds
mass (m) has units of kilograms
height above ground (h) has units of meters
velocity (v) has units of m/s
acceleration (a) has units of m/s2
ratio of the ramp (R) has is unitless
acceleration due to gravity (g) is 9.8 m/s2
Kinetic energy (KE) has units of J
Potential energy (PE) has units of J
KE = ½ mv2
PE = mgh
v = d/t
vfinal = vinitial + a*t
R = (height of ramp)/(length of ramp)
a = g*R
Basic physics concepts. Most of the concepts included in this activity are explained in detail in
a middle school physical science or high school physics text book. Therefore, extensive
explanations about velocity, acceleration, and gravitational acceleration are not included in the
teacher notes for this activity.
Part 1 Notes
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Potential energy. The potential energy of an object is the amount of energy stored in that
object as a result of it being displaced a given height. Potential energy of an object depends on
both its mass and its height above the ground.
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Mass of milk carton cars. A good ballpark figure for the mass of the milk carton car is about
0.0175 kg. However, depending on whether or not you vary any of the materials for the cars,
you will need to have your students mass their cars so they can compute the PE and KE.
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Measuring times and distances. Please consult Figure 2 in the student handout to help
students understand where and when they need to record times and distances in this activity.
Make sure students understand that time needs to be measured only while the car is on the ramp.
Also, make sure the students only measure the distance from the bottom of the ramp to where
the car comes to a stop on its own stops - they should not include the length of the ramp in their
measurement of the distance the car traveled once off the ramp.
Kinetic and Potential Energy
Teacher Notes
1
Part 2 Notes
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Kinetic energy. Kinetic energy is the energy associated with a moving object. As your
students will see in this activity, the kinetic energy of an object depends upon both its mass and
how fast it is moving.
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Rationale for using Ramp Ratio. The ramp ratio (R) is used in this activity as an alternative to
using the basic trigonometry that would normally be used to find the y component of the
gravitational acceleration for an object rolling down an incline. Here is the derivation:
 height of ramp 

sin θ = 
 length of ramp 
ay = g sin θ
F = ma
mg sin θ = ma
a = g sin θ
 height of ramp 
 ;
a = g 
 length of ramp 
a=gR
(Recall that there is no x component to gravitational acceleration.)
 height of ramp 

R = 
 length of ramp 
Part 3 Notes
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Mass of washers. Depending on the type of washers you use, the masses will vary. A good
ballpark figure is 0.0066 kg (or 6.6 g) per washer.
Part 4 Notes
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Relationship between kinetic and potential energy. (This explanation pertains to questions
#35 to #41 in the Student Handout) While energy is never created nor destroyed, it most
certainly is converted from one form to another. In this activity your students build a car made
from a milk carton. This car is be placed at the top of a ramp and released. Before the car starts
to descend the ramp, it has potential energy associated with its height above ground; however, it
has no kinetic energy because it is not moving. Once the car starts to roll down the ramp, it
picks up speed (accelerates). Thus the potential energy of the car is converted into kinetic
energy. Once the car reaches the bottom of the ramp, all of its potential energy has been
converted into kinetic energy. In addition to calculating the kinetic and potential energy of a
milk carton car, your students should be assisted in seeing the relationship between kinetic and
potential energy, and how the mass of the car affects its kinetic and potential energy.
Notes on Materials
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Materials. Most of the materials listed in this lesson plan can be found at a standard store. The
washers, axles, and cardboard wheels could be purchased at a hardware store.
Kinetic and Potential Energy
Teacher Notes
2
Name:________________________
Kinetic and Potential Energy
(An Introduction to the Physics of Motion through the use of Milk Carton Cars)
Overview
During this activity you will build a car using a milk carton and then observe how this car behaves
as it travels down a ramp. You will learn about kinetic and potential energy so that you can explain
what you observe. Have fun!
Part 1 (What is potential energy?)
1) Build the milk carton car as described in the Additional Resources section of the handout.
2) Use the wooden board (or some other flat surface) and a stack of books to create a test ramp.
Be able to adjust the height of the ramp to 0.1, 0.2, and 0.3 meters. Keep in mind that…
0.1 m = 10 cm
0.2 m = 20 cm
0.3 m = 30 cm
3) Set the ramp height to 0.1 m by adjusting your stack of books appropriately. (Refer to Figure
1.)
HEIGHT
Ramp
Figure 1. Ramp height.
4) Now take some time to study Figure 2. Figure 2 describes the two things you want to measure
as you as you observe your car go down your ramp.
a) The time it takes for your car to roll down the ramp.
Kinetic and Potential Energy
Penn State University GREATT Project
Student Handout
1
b) The distance your car travels from when it reaches the bottom of the ramp to when it comes
to a complete stop on its own.
You will want to record both of these measurements in Table 1.
Begin timing here
End timing here;
Begin measuring distance from here
HEIGHT
Figure 2. Car and ramp, showing where to begin timing and measuring.
Notice from Figure 2 that the time you are measuring only involves the time
your car spends on the ramp. It does not include any time your car spends rolling
once it is off the ramp.
Also notice from Figure 2 that the distance you are measuring does not
include the length of the ramp. Only measure the distance between the base of the
ramp and the point at which your car comes to a stop by itself.
5) Obtain the time and distance for each ramp height (0.1m, 0.2m, 0.3m). To reduce error,
measure the time and distance three times for each height. Record all of your data in Table 1.
6) Compute the average time and average distance for each ramp height and record these values in
the gray shaded area in Table 1.
7) Mass your car on a balance, and record it in the appropriate space in Box #1. Notice that you
need to record this value in kg, so remember that…
1000g = 1kg.
8) Read about potential energy in the Additional Resources section of this handout. Describe
what potential energy means IN YOUR OWN WORDS. Use the box provided.
In my own words, potential
Kinetic and Potential Energy
Penn State University GREATT Project
energy means….
Student Handout
2
9) Will your car have the same or different potential energy when the height of the ramp changes?
Make your prediction in the box provided.
Will my car have the same or different potential energies when the height of the ramp
changes?
10) Using the information provided in Box #1, compute the potential energy (PE) of your car when
it was sitting at the top of the ramp. Show your work for this calculation in Box #2, and then record
this number in the appropriate space in Table 1.
Box #1. Equation for potential energy.
PE = m·g·h
m = the mass of the car (kg)
g = 9.8 m/s2 (acceleration due to gravity)
h = height of the ramp (meters)
* My car has a mass of _________________kg
* The calculated PE will have units of Joules (J) *
Box #2. The PE of my car when the ramp height is 0.1 meters.
The PE of my car at the top of the ramp that is 0.1 meters high
11) Repeat steps 3-7 with the ramp adjusted to a height of 0.2 m and also to a height of 0.3 m.
Record your data in Table 1.
Kinetic and Potential Energy
Penn State University GREATT Project
Student Handout
3
Table 1
Height
of
ramp
(m)
Trial 1
Time
(sec)
Distance
(m)
Trial 2
Time
(sec)
Trial 3
Distance
(m)
Time
(sec)
Distance
(m)
Averages
Time
(sec)
Distance
(m)
PE
(J)
0.1
0.2
0.3
Part 2 (What is kinetic energy?)
By now, you’ve calculated the potential
energy of your car while it was at the top of the ramp
for three different ramp heights (0.1 m, 0.2 m, and 0.3 m). Does your car also have kinetic
energy?
12) Read about kinetic energy in the Additional Resources section of this handout. Describe what
kinetic energy means IN YOUR OWN WORDS. Use the box provided.
In my own words, kinetic
energy means….
13) Does your car have any kinetic energy when it is resting at the top of the ramp before it begins
moving down the ramp? Explain / justify your answer.
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
14) Using the information provided in Box #3, compute the kinetic energy (KE) of your car when it
is at the top of the ramp but has not yet started moving. (Hint: what is the velocity of your car when
it is not moving?)
Show your work for this calculation in Box #4.
Kinetic and Potential Energy
Penn State University GREATT Project
Student Handout
4
Box #3. Equation for kinetic energy.
KE = ½ mv2
m = mass of the car (kg)
v = the velocity of the car at the bottom of the ramp
*KE has units of Joules (J)
Box #4. The kinetic energy of my car at the top of the ramp before it started moving down the
ramp.
The KE of my car at the top of the ramp before it has starts moving
15) Does your car have any kinetic energy when it is reaches the bottom of the ramp? Explain /
justify your answer.
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
16) In order to find the kinetic energy of the car at the end of the ramp, you’re going to need the
velocity of the car at that point.
Let’s call the velocity at the end of the ramp the final velocity of the car
(vfinal) and the velocity at the top of the ramp the initial velocity (vinitial).
Box #5 provides the equation for determining the velocity of an object at the
starting and ending points of its path.
Kinetic and Potential Energy
Penn State University GREATT Project
Student Handout
5
Box #5. Equation for velocity.
vfinal = vinitial + a·t
a = acceleration of the car in m/s2
t = time it took the car to travel down the ramp (seconds)
vfinal and vinitial have units of m/s
17) Since your car was initially at rest at the top of the ramp, vinitial = 0. Therefore, if:
vinitial = 0; and
vfinal = vinitial + a·t,
show how:
vfinal = a·t.
Show your work in Box #6.
Box #6. How does vfinal
= a·t?
How vfinal = a·t
18) Before moving on, remind yourself what vfinal,
in the space provided.
Vfinal
=
a
=
t
=
a, and t actually mean.
Write their meanings
19) To find the velocity of your car once it reaches the bottom of the ramp, you need the
acceleration of your car and the time it took your car to go down the ramp. Which value do you
already have, and which value do you still need? Complete Box #7 to answer these questions.
Kinetic and Potential Energy
Penn State University GREATT Project
Student Handout
6
Box #7. Values needed to calculate vfinal.
Values needed to calculate vfinal
We have:
acceleration
/
time
(circle one)
We need:
acceleration
/
time
(circle one)
20) Recall that the acceleration due to gravity was defined in Box #1 as:
g = 9.8 m/s2
21) The acceleration of your car down the ramp will depend on the acceleration due to gravity and
the angle the ramp makes with the ground (see Figure 3).
Angle ramp makes w/ ground
θ
Figure 3. Angle the ramp makes with the ground.
However, instead of trying to find the angle, we can instead just find a ramp ratio for each of the
three different ramp heights you used (0.1m, 0.2m, and 0.3m).
The ramp ratio is defined in Box #8.
Box #8. Equation for ramp ratio.
Ramp Ratio, R
R
height
length
of ramp 
of ramp 
22) Explain why the ramp ratio is directly related to the angle your ramp makes with the ground for
different heights. Record your explanation in Box #9. Use Figure 4 to help you.
Kinetic and Potential Energy
Penn State University GREATT Project
Student Handout
7
Length of ramp
Height of ramp
θ
Length of ramp
Height of ramp
θ
Figure 4. How angle ramp makes with the floor is related to the ramp ratio.
Box #9. Why ramp angle is directly related to ramp ratio.
Why ramp angle is directly related to ramp ratio
(Hint: What changes as the height changes?)
23) Remind yourself why we are concerned with angles and ramp ratios by reviewing Box #7 and
then questions #16 and #21. What are we ultimately trying to find? Write your reminder in the
space provided.
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
24) Calculate R for each of the three ramp heights (0.1 m, 0.2 m, and 0.3 m) and record your
answers in Table 2.
Kinetic and Potential Energy
Penn State University GREATT Project
Student Handout
8
Table 2
Height (m)
a (m/s2)
R
0.1
0.2
0.3
25) Now find the acceleration of your car for each ramp height, using the equation for acceleration
provided in Box #10. Record your values for acceleration in Table 2.
Box #10. Equation for acceleration in terms of ramp ratio.
a = g*R
a = acceleration of the car in m/s2
g = 9.8 m/s2
R = the ramp ratio (unitless)
26) Recall the equation for vfinal:
vfinal = a·t
Calculate the velocity of your car at the bottom of the ramp (vfinal) for each ramp height. Use the
accelerations you recorded in Table 2, and use the average times you recorded in Table 1 for each
ramp height. Enter the velocities for each ramp height into Table 3.
Table 3
Height (m)
Average time
(sec)
[From Table 1]
a (m/s2)
[From Table 3]
vfinal
(m/s)
0.1
0.2
0.3
27) Review Box #3 (equation for kinetic energy), and then calculate the kinetic energy (KE) of
your car at the bottom of the ramp for each ramp height. Enter your calculated values for KE into
the appropriate spaces in Table 4.
Kinetic and Potential Energy
Penn State University GREATT Project
Student Handout
9
Table 4
Height
(m)
Velocity
(m/s)
Potential Energy at
the top of the ramp
(J)
Kinetic Energy at the
bottom of the ramp
(J)
0.1
0.2
0.3
28) Re-enter your calculated values for potential energy (PE) into Table 4.
Part 3 (Mass and Energy)
Now you’re going to add some weight to your car! What do you predict will happen? Do you think
the car will perform differently?
29) Make a prediction about what you think will happen to your car when you add some washers to
the paper cup, and write it in the box provided.
My prediction about what will happen to our car when weights are added
30) To find out what happens when weight is added to your car, follow the directions provided:
Choose any height (0.1 m, 0.2 m, or 0.3m) to do this part of the activity. The
particular height you choose does not matter, but you will need to keep this height
constant while doing this particular part of the activity.
Set up the ramp at the height you chose.
Fill in the appropriate information for 0 washers in Table 5. Use the values
you found in the earlier parts of this activity for the particular ramp height you
decided on.
Add 6 washers the cup of your car.
Prepare to record the time it takes your car to go down the ramp AND the
distance it travels from the base of the ramp (just as you did in Part 1; see Figure 2)
Hold the car at the top of the ramp and release it (your car should not have
any washers in it yet). Record the time and distance in Table 5.
Now place 6 more washers in the cup of your car (for a total of 12).
Record the time and distance for 12 washers in Table 5.
Kinetic and Potential Energy
Penn State University GREATT Project
Student Handout
10
Table 5
# of
washers
Time it takes Distance traveled
to travel
from base of ramp
down the
(m)
ramp
(sec)
Potential
Kinetic Energy
Energy at the at the bottom
top of the
of the ramp (J)
ramp (J)
0
6
12
31) Recall the equations for kinetic and potential energy are as follows:
PE = m·g·h
KE = ½ m·v2
If you need to refresh your memory about what m, g, h, and v mean, do so at this time.
32) When you added washers to your car, what value were you manipulating / changing in the
equations for potential and kinetic energy?
Circle One:
mass / gravitational acceleration / height / velocity
33) Obtain the mass of one washer, and record it in Box #11. Calculate the total mass of your car
with 6 and 12 washers, and record these values in Box #11 also.
34) Using the values you entered in Box #11 and any other information you recorded in Table 5,
calculate the potential and kinetic energy of your car with 6 and 12 washers. Record these values in
Table 5.
Box #11. Masses of washers and car.
Mass of one washer: ______________________kg
Mass of your car:
______________________kg
Mass of your car w/ 6 washers:
______________________kg
Mass of your car w/ 12 washers:
______________________kg
Kinetic and Potential Energy
Penn State University GREATT Project
Student Handout
11
Part 4 (Making sense of what happened in this activity)
Now that you have completed the activity, take some time to analyze and interpret the data you
have collected by discussing the following questions with your group.
35) As the height of the ramp increased, did the potential energy of your car while it was at the top
of the ramp increase or decrease? Use evidence from this activity to support your answer.
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
36) What can you say about the relationship between the distance the car traveled from the base of
the ramp and the potential energy it had at the top of the ramp?
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
37) Is there any relationship between the distance the car traveled from the base of the ramp and the
amount of kinetic energy it had when it reached the base of the ramp?
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
38) Was the kinetic energy of the car at the base of the ramp the same or different as the potential
energy of the car at the top of the ramp?
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
39) What does your answer to #38 tell you about energy conservation?
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
40) When you increased the total mass of the car by adding washers, did the car travel a shorter or
farther distance?
________________________________________________________________________________
41) Use the terms “potential energy” and “kinetic energy” to explain your answer to #40.
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
Kinetic and Potential Energy
Penn State University GREATT Project
Student Handout
12
Additional resources
Potential energy: the amount of energy stored in an object as a result of that object’s height; the
potential energy of an object depends on both its mass and its height above the ground.
Kinetic energy: the energy associated with a moving object; the kinetic energy of an object
depends upon both its mass and how fast it is moving; an object completely at rest does not have
kinetic energy.
How to build your milk carton car
1) Poke a hole into the side of the milk carton with a pen or pencil and use that hole as a starting
place to begin cutting for the larger hole.
2) Cut a 2 inch diameter hole into the top of the carton and insert the cup into the hole. Make sure
the cup is secured by taping the brim of the cup to the carton. See picture below.
Front Side
3) On the opposite side of the milk carton, use a ruler to draw a line for axle placement. There
will be two axles: one axle ½ inch from the bottom of the carton and one axle ½ inch from the top
of the carton. Both of these lines should be drawn on the side opposite the side where the cup is.
See picture below.
1/2
1/2
Axle lines (1/2 inch from ends of carton)
4) The long drinking straw will be used as axle “sleeves”. Cut the straw in half and tape each half
on the axle guidelines you drew in step 3. See picture below. Be careful not to crush the straw!
Kinetic and Potential Energy
Penn State University GREATT Project
Student Handout
13
Each half of long drinking straw serves as an axle sleeve.
5) Slide the axles into the axle sleeves.
6) Gently slide the cardboard wheels onto the ends of the axles. The wheels should be pushed
onto the axles by only 1/8 inch or so. See picture below.
Cardboard wheels pushed 1/8 inch onto each axle.
7) Make sure the axles spin freely! If not, correct what may be rubbing or is too tight.
8) Hot glue or glue the wheels on the axles. Make sure the wheels are straight; otherwise, they
will wobble as they roll.
9) Your final car should look like the pictures below:
Rear View
Kinetic and Potential Energy
Penn State University GREATT Project
Side View
Student Handout
14