Kinetic Energy and Potential Energy
Aim: The aim of this experiment is to adjust the height of the ramp
and measure the changes in motion. Also, the realtionship between
gravitational potential and kinetic energy is to be found.
An object can store energy as the result of its position.
For example: the heavy ram of a pile driver is storing energy when it
is held at an elevated position. (As shown in diagram). This stored
energy of position is referred to as potential energy
Potential energy is the stored energy possessed by an object.
Gravitational potential energy
is the energy stored in an object as
the result of its vertical position (i.e., height). The energy is
stored as the result of the gravitational attraction of the Earth for
The gravitational potential energy of the heavy ram of a pile driver
shown above is dependent on two variables - the mass of the ram and
the height to which it is raised. There is a direct relation between
gravitational potential energy and the mass of an object; more massive
objects have greater gravitational potential energy. There is also a
direct relation between gravitational potential energy and the height
of an object; the higher that an object is elevated, the greater the
gravitational potential energy. These relationships are expressed by
the following equation:
PEgrav = mass * g * height
where g = gravitational constant (9.8 m/s)
Kinetic energy is the energy of motion.
An object which has motion - whether it is vertical or horizontal
motion - has kinetic energy.
There are many forms of kinetic energy:
Â· Translational (the energy due to motion from one location to
Â· vibration (the energy due to vibration motion),
Â· rotational (the energy due to rotational motion)
This investigation will focus on translational kinetic energy.
The amount of translational kinetic energy of an object depends upon
1. the mass (m) of the object and
2. the speed (v) of the object.
The following equation is used to represent the kinetic energy (KE) of
where m = mass of object (Kg)
v = speed of object (m/s)
Potential and Kinetic Energy
Potential energy is the capacity for doing work that a body possesses
because of its position or condition. For example, a stone resting on
the edge of a cliff has potential energy due to its position in the
earthÂ’s gravitational field. If it falls, the force of gravity (which
is equal to the stoneÂ’s weight) will act on it until it strikes the
ground; the stoneÂ’s potential energy is equal to its weight times the
distance it can fall.
Kinetic energy is the energy a body possesses because it is in motion.
The kinetic energy of a body with mass m moving at a velocity v is one
half the product of the mass of the body and the square of its
velocity, i.e., KE = 1/2mv2. Even when a body appears to be at rest,
its atoms and molecules are in constant motion and thus have kinetic
The difference between kinetic energy and potential energy, and the
conversion of one to the other, is demonstrated by the falling of a
rock from a cliff, when its energy of position is changed to energy of
motion. Another example is provided in the movements of a simple
pendulum. As the suspended body moves upward in its swing, its kinetic
energy is continuously being changed into potential energy; the higher
it goes the greater becomes the energy that it owes to its position.
At the top of the swing the change from kinetic to potential energy is
complete, and in the course of the downward motion that follows the
potential energy is in turn converted to kinetic energy.
Hypothesis: As the height of a ramp increases, potential and kinetic
energy will increase. Also, the total potential energy before the ball
is released, at the top of the ramp should equal to the total kinetic
energy of the ball at the bottom of the ramp.
The experiment is based on the potential energy at the top of the ramp
being converted into kinetic energy at the bottom. I predict that the
higher the ramp the faster the ball will travel down it.
Increase in height of ramp=increase in velocity of trolley
Equations/Units/Ranges to be used
To make this investigation successful, a sensible range must be chosen
and also the amount of readings to record in order to come up with a
useful and informative outcome. For example, in the experiment it
would be pointless to experiment with heights ranging from 1cm-2cm
because the speed difference would be minor. Instead a more sensible
range, such as from 10.0 cm-25.0 cm, would be appropriate to yield
useful results. The readings should be taken at 2-5 cm intervals,
and a minimum of three readings should be taken on each height to work
out an average (this makes the end result more accurate).
Below is a clear list of the ranges and amounts in my two experiments.
Experiment-three tests on each height, starting from 11.0 cm
PEgrav = mass * g * height
where g = gravitational constant (9.8 m/s)
KE = Â½ * m * vÂ²
where m = mass of object (Kg)
v = speed of object (m/s)
The formula that will be proved in the experiment is EK = EP.
PEgrav = KE
mass * g * height = Â½ * m * vÂ²
g * height = Â½ * vÂ²
9.8 * height = Â½ * vÂ²
Â· Metres (metre ruler to measure height)
Â· m/s [for velocity, as it is the displacement of an object over time
Â· Kg ( unit for mass of the ball) **not required**
Â· 9.8 m/s (gravitational constant)
It is important to control all other variables except the height of
the ramp during the practical, to ensure fair and accurate results.
The final velocity of the ball is a dependent variable, as it is
expected to change according to the height from which the ball is
released. Finally, the mass of the ball does not need to be altered,
as it does not relate to the result of the experiment as shown below.
Â· Velocity- The final velocity of the ball depends on the height at
which the ball is released each time.
Â· Height of ramp - as this is included in the formula for potential
energy, the height of the ramp will affect the speed of the trolley. I
will be modulating this variable in the experiment, and therefore, it
is a independent variable.
Â· Mass and type of ball - mass is also included in the formula for
potential energy and so could affect the speed of the trolley one way
or the other. With this experiment, the mass and the type of ball used
will be kept constant as it is not required to be manipulated as shown
Â· Gravity - the last portion of the formula for potential energy is
gravity, which will affect the outcome if it is increased or
decreased. Since the experiment is being performed on earth, the
gravitational constant (9.8 m/s) remains the same throughout the
Â· Friction- Friction is one of the factors may use some of the energy
when it is being converted into kinetic (movement) energy as the ball
moves down the ramp. The friction between the ball and the surface of
the ramp can use up some of the potential energy used to move the ball
and convert it to heat instead. This can slow down the trolley, but
only very slightly. To maintain the same friction for all the results
we should use the same material for the surface of the ramp, and the
same type of ball throughout the experiment. No grease should be added
to lubricate any equipment.
Â· Size of the ramp- The size of the ramp should be kept constant to
prevent any differences in the results.
Â· Positioning of the laser beam to measure the final velocity- The
position of the laser beam has to remain the same throughout the
practical, to ensure the results found are fair and accurate. Also,
the position of the laser beam should be right at the bottom of the
ramp to find out exactly, how the change in height affects the
velocity of the ball.
With this straightforward experiment there is not much that needs to
be taken into consideration. No harmful substances are being used,
neither are flames or solvents, hence, there are no safety concerns.
All-in-all it is a relatively safe experiment. Obviously the need to
take precautions when releasing the ball at different heights is
necessary, as well as refraining from watching the ball too closely,
as it may hit the eyes or face.
Also, at the bottom of the ramp some sort of barrier will need to be
placed to prevent damage to the ball as it hurtles off the edge, or to
thwart potential harm to any unsuspecting person.
Â· 1 cardboard box (A4 size)
Â· 1 ramp (metal or wooden)
Â· masking tape
Â· 2 cardboard sheets (thin)
Â· laser equipment
Â· 1 wooden block ( acts as a stopper for ball)
Â· metre ruler
Â· 2 wooden blocks
Â· blue tag
Â· ball (30mm)
Â· capacitor (50v)
Â· power supply
Reasons for choosing apparatus:
Â· 1 cardboard box (A4 size): For one side of the ramp to rest on, to
increase the height of the ramp summit
Â· 1 ramp (metal or wooden): For the ball to roll down
Â· ball (30mm): To roll down the ramp
Â· Masking tape: To keep the cardboard sheets on the ramp securely
stuck to the bench.
Â· 2 cardboard sheets (thin): To keep the level of the ramp, same to
the bench, allowing the ball to roll down smoothly.
Â· Laptop: Used for the program required to measure the velocity of the
ball as it passes the laser beam.
Â· Laser equipment: To effectively and accurately measure the final
velocity of the ball as it passes through, at the bottom of the ramp.
Â· 1 wooden block ( acts as a stopper for ball) : To stop the ball from
flying off the bench
Â· Metre ruler: To measure out the different heights on the ramp.
Â· 2 wooden blocks: To keep the laser beam at a suitable height, so
that it hit the ball right in the middle, as it rolled through.
Â· Blue tag: To firmly stick the laser equipment on the wooden blocks.
Â· Capacitor (50v): To provide charge for the laser equipment to run.
Â· Power supply: Used to provide charge for the laser equipment.
Â· Pencil - To mark the start (different heights) and finish lines.
Â· Data Collection Sheet - To record the results on
Â· Stationary - To write the results down with
Â· Calculator Â– To calculate average velocity
Below is a diagram of how the equipment will be set up and used.
1. Collect all materials
2. Set out equipment as shown in the diagram above
Â· Measure the diameter of the ball with the metre ruler.
Â· Place an A4 size box on the table/bench
Â· Put the ramp on the box
Â· Stick the cardboard sheets onto the ramp, to make the ramp level to
Â· Connect the laser equipment to the laptop and power supply
Â· Ensure that the laser beam goes through the middle of the ball being
Â· Begin marking different heights on the ramp.
3. Ensure the height at the start line (the summit of the ramp) is
10.0- 15.0 cm using the metre stick
4. Hold the ball with its front touching the start line
5. Simultaneously start the velocity measuring program and then,
release the ball (be careful not to push it or exert any extra force
6. Ensure that the ball has travelled in a more or less straight line,
to increase accuracy in the results.
7. Record the time taken for the ball to reach the finish(wooden
barrier), next to the relevant height, in a table
8. Repeat Step 4 twice more so you end up with three results for the
same height then continue onto step 9
9. Add all these results together and divide the answer by three to
obtain the average.
10. Record this average in the table as well.
11. Using the metre ruler, measure another height, around 1.0-5.0 cm
higher then the one used previously.
12. Repeat Step 4 until you have obtained results for at least another
six to seven heights.
13. For each different height, repeat Step 4 twice to get at the
average of three results.
14. Record all the results on the table.
How variables were kept constant:
The variables were kept constant by ensuring that they were
controlled. The most important variables that was to be controlled was
the positioning of the laser equipment and the mass/type of ball used
on each try.
Difficulties encountered and how they were overcome:
Â· Accuracy of measurements: used a metre ruler to measure
Â· Making sure the ball travelled in a straight line: Tried to release
the ball as straight as possible and repeated the trial if the final
velocity seemed to be to big or small as compared to the others
Â· Ensuring that the laser beam went through the middle of the ball:
put the laser equipment atop a wooden block, to keep level with ball
Â· Accuracy of final velocity: conducted three trials for each height
The results obtained were as accurate as possible, and covered a range
of heights from 11.0 centimetres to 25.0 centimetres and not above
that, as the length of the ramp did not allow so. Also, the results
obtained were narrowed to Â± each side of the result. Lastly, the
results from three different trials for each height were obtained and
then averaged to ensure accuracy.
Height (cm) Â±0.5
Average Velocity (m/s)
Â± Average Velocity (m/s)
* All results to 4 decimal
Graphs: on next page
Analysis of results:
The data collected relates to the aim, as the results show what the
final velocity of the ball, at the bottom of the ramp is, for the
different heights from which the ball was released. The results
obtained were able to be used, to prove the relationship between
gravitational potential energy and kinetic energy.
The graph, of the average velocity versus the height of the ramp
clearly shows an increase in speed as the height of the ramp greatens,
but not in a proportional manner. The slight curve suggests that
another force such as friction or air resistance might be acting on
the ball and not permitting it to increase speed uniformly.The
friction of the ramp or some air resistance may have caused the ball
to go faster or slower.
Nevertheless, the results cearly show that the higher the ramp the
faster the speed of th abll. This can be explained. The higher an
object goes the more gravitational potential energy it gains. When the
ball rolls down its potential energy is converted into kinetic energy
and since energy can neither be destroyed or created, and only
converted; it will move at a faster speed. So therefore height does
affect the speed at which an obejct travels down a ramp.
In the second graph, âˆš Velocity versus height, a straight line was
obtained, showing that there was a relationship between the height of
the ramp and the âˆš velocity. This can be seen by the following working
First of all I am going to calculate the average potential energy at
Potential energy = gh (mass not required)
Then, the average kinetic energy at each height.
Kinetic energy = 0.5 x (velocity)Â² (mass not required)
(tanle on next page)
Potential energy (J)
Kinetic energy (J)
9.8 x 0.11
Â½ x 0.8017
9.8 x 0.13
Â½ x 0.933
9.8 x 0.15
Â½ x 1.0353
9.8 x 0.17
Â½ x 1.1539
9.8 x 0.19
Â½ x 1.3617
9.8 x 0.21
Â½ x 1.5107
9.8 x 0.23
Â½ x 1.6903
9.8 x 0.25
Â½ x 1.9379
Graph of Potential and Kinetic Energy
The graph above, on overall shows that as the height increases the
potential and kinetic energy increases. The higher the object is the
more energy it gains as you can see on the above graph where it
displays potential and kinetic energy. Hence, the higher the height
from which the ball is released, the more the potential energy
converted into kinetic energy, resulting in the incresing velocity.
Higher the object = more energy gained
Potential Energy = Kinetic energy
From the above analysis, it is evident that as the height from which
an object is increased, the potential energy stored in an object
increases as well. This energy is converted into kinetic energy, which
results in the increasing velocities of the ball. However, in the
above investigation, potential energy â‰ kinetic energy. This is
probably because some of the energy was lost to friction as heat
energy. Also, some errors in the calculation of the heights may have
resulted in the inequality between the gravitational potential energy
and kinetic energy of the ball.
The experiment went very well and ran efficiently, thanks to the plan
we had drawn out beforehand. The laser equipment helped to make sure
that our results were accurate and could be counted on. For our
experiment, we didnÂ’t require it to be as accurate as the computer
system allowed so we rounded the results off to four significant
The results found helped us to prove that if the same object is used
in all trials, then the mass variable can be removed from the equation
of kinetic energy and potential energy. Also, the results found proved
our hypothesis, that as we increased the height from which an object
is released, its velocity will increase as well, as a result of the
gravitational potential energy stored in the object before release is
converted into kinetic energy in the form of its velocity.
In terms of the accuracy of our results, there were some errors and
inequalities which may have resulted because of several reasons such
as errors in measuring the heights, energy loss due to friction and
maybe the ball not traveling in a straight line.
If I were to do this experiment again, I would experiment with
different surfaces of ramp. Also I would try to use a trolley instead,
that travelled in a straight line! The main problem we found in our
experiment was that the ball kept swaying to the sides, as the heights
increased, creating a longer journey and resulting in the slightly
inaccurate results. This could have been due to an uneven surface on
the ramp, or because the ball was not released in a straight line.
Nevertheless, the investigation proved the point we were trying to
find out, which was that the potential energy stored in an object
increases as the height from which it is released increases, and this
in turn increases its final velocity.
Limitations of apparatus and measuring equipment:
Â· Ball not rolling down the ramp in a straight line
Â· The metre ruler, had to be put vertically to measure the height, and
may not have been accurate.
Â· Uneven surface of cardboard sheets resulted in friction, causing the
ball to lose some energy as it rolled down
Â· Ball was too light, and therefore swayed to the sides as it rolled
Uncertainty of data and calculations:
Â· Making precise points, for the different heights, due to parallax
Â· Estimation of where to draw point for each height, resulting in a
Â±0.5 cm inequality
Â· Some of the results were not very accurate resulting in some
Expected and derived relationships or physical values:
Â· The expected result for the relationship of the height from which
the ball was released and its velocity was that as the height
increased the velocity of the ball would increases as well. This is
also due to the fact that as the height increases, the potential
energy stored in the ball increases, and so consequentially so does
the kinetic energy and therefore the velocity of the object increases
as well. The derived results are quite accurate, due to the result
being obtained and averaged out by obtaining results of three other
trials. However, the results can be further improved by using a
frictionless surface for the ramp and also using a trolley to ensure
it travels in more or less a straight line. This would make it easier
to obtain accurate results and find a more accurate relationship
between the potential energy of an object at different heights and its
The investigation of the relationship between the height of the ramp
and the final velocity of the ball was more or less a success. The
relationship between potential and kinetic energy was more or less
found and proved, despite some inequalities in the results. Also, the
gradient, the graph, for kinetic and potential energy was a constant,
showing that the total kinetic energy of an object is proportional to
its potential energy.