Lab 12: Energy Relationships in an Inclined Plane
When a ball rolls down an inclined plane potential energy (PE) is
converted into kinetic energy (KE). This is a beautiful example of
energy conservation. A small amount of energy is converted into heat
as the ball moves air out of its way due to air resistance. A small
amount of energy is also converted to energy of rotation as the ball
spins down the track. Nevertheless, energy is conserved if we take
these two factors as being negligible. Similarly, when a roller coaster
rolls from the top to the bottom of a hill, PE is converted to KE. In
today’s lab we will explore the principle of energy conservation and
see how it applies to a ball rolling down a hill.
Procedure:
1. Set up the ramp for the steel ball. Measure the vertical height
(hb) of the ball from the ramp surface’s lowest position. Record
this value.
2. Measure the mass (m) of the ball in kg. Record this value.
3. Calculate the PE of the ball (PE = mgh where g is 9.81 m/s2.
Record this value.
4. Calculate the velocity of the ball as it leaves the ramp using the
formula for KE (KE = ½ mv2). Record this value.
5. Measure the ‘drop’ height of the ball (ht) from the edge of the
ramp to the ground. Be sure that this measurement is not at
some angle. Record this value.
6. Using the equations that you became familiar with when
studying projectile motion and your knowledge of that topic to
calculate the range (d) of the ball when it leaves the ramp.
Assume that the ball is perfectly horizontal at that time. Record
this value.
7. Place a target at the predicted location and let your projectile fly!
Record its actual range.
8. Repeat the experiment but this time, use a photogate to
measure the velocity of the ball as it leaves the ramp. The setup for this will be demonstrated by your teacher. You will need
to open the Probes and Sensors folder in Vernier and choose
Photogates followed by Single Gate Timing. Record this velocity
(vphoto) and proceed as before, calculating the new range based
on this data.
Data:
Run 1 (No Photogate)
hb
(m)
M
(kg)
PE
(J)
V(calculated)
(m/s)
PE
(J)
V(photo)
(m/s)
KE (J)
ht
(m)
d
(m)
KE (J)
ht
(m)
d
(m)
(calculated)
Run 2 (Photogate)
hb
(m)
M
(kg)
(calculated)
Analysis:
1. Calculate the % difference between the actual range and the
predicted range of the ball.
2. How far did the ball land from your predicted landing point? Is it
short, long or relatively close? Close would be within a few %.
3. Compare your findings with that of the rest of the class. Is there
a pattern to the results?
4. How would you account for the discrepancy between the
predicted and actual landing points?
5. Compare the velocity found in step 8 to the calculated velocity in
step 4. The value found in step 8 should be consistently less.
Why do you think this is so?
6. Based on your results, what conclusion can you reach about
energy conservation in this experiment?