Download POTENTIAL AND KINETIC ENERGY Experiment 1 Tilted Air Track

POTENTIAL AND KINETIC ENERGY
 The energy
When an object is lifted vertically upward with no increase in speed, the work done in lifting W = F  h.
used in lifting is "stored" in the form of potential energy. Since gravity continues to act on the object it does the same amount of
work on the way down, causing the object to increase its speed and therefore its kinetic energy, 12 m v . Hence the change in
potential energy, mg h, where h is measured vertically, is equal to the change in kinetic energy.
Experiment 1
Tilted Air Track
Photogate #2
photogate #1
Inclined Air Track
Another way of viewing this is:
or
PEi  KEi
PEi  PEf 
 PEf  KEf
KEf  KEi
Conservation of Energy
* Measure the vertical height from the top surface of the air track to the table top at the position of gate #1 and gate #2 (make sure
they are properly plugged in).
* Open Science Workshop. Move the icon Phoneplug to digital 1 input ...select Photogates (2)
* Move table icon to digital 1 input
* Choose velocity v1 & velocity v 2, then enter the length of the glider 0.128 m. The time the glider takes to pass each gate is used
to calculate the velocity of the glider at each gate (length of glider / time the gate is blocked).
* Measure the mass of the glider.
* Calculate the P.E. and the K.E. at gate #1 and the P.E. and K.E. at gate #2. You should repeat the measurements for several
starting points. You should change the mass (add weights to the glider). You could also give the glider a small push at the bottom
of the incline and have it slow down as it goes up the incline converting kinetic energy into potential energy. Record your data and
calculations in Table 1.
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Experiment 2
The Vertical Tube
Vary the distance, h, and measure the velocity.
Tabulate the mass, h, t, v, PE , KE. Compare PE with KE.
Knowing the length, L, of the cylinder and the time, took
t, itto pass the photogate, you can calculate the velocity
with L / t and then calculate the KE = 1/2 m v .
Another way of viewing this is:
or
PEi  KEi
PEi  PEf 
 PEf  KEf
KEf  KEi
Conservation of Energy
* Measure L, h , h2 , v , v , and record these data in Table 2.
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Data Sheet
Name _______________________________
Date ____________
Group # ____
Lab Partners _______________,___________________
Table 1. (inclined air track)
h 1 t1 h 2
v1 v2 (PE1 + KE1 )
(PE2 + KE2 )
% diff.
mass
h1
h2
v1
v2
(PE+KE)1
(PE+KE2)
(grams) (cm)
(cm)
(cm/s) (cm/s)
(ergs)
(ergs)
% diff
What is the % uncertainty in each measurement: mass, height velocity and lastly in the calculated Energy?
Questions to guide your discussion of results:
Did the decrease in potential energy equal the increase in Kinetic Energy?
When you sent the glider up the incline was the decrease in Kinetic Energy equal to the increase in Potential Energy?
Table II (vertical tube) L = ...........cm
mass
h1
h2
v1
(grams) (cm)
(cm)
(cm/s)
v2
(cm/s)
(PE+KE)1
(ergs)
(PE+KE2)
(ergs)
% diff
Questions
Both procedures used a straight path for the object. What if the path was curved, would the energy be
conserved? Consider two paths where the starting points are at the same altitude and the ending points are at
the same altitude. Will the ball have the same velocity at the bottom? Will the ball arrive at point B at the same
time for each path? Which will arrive first?
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CHALLENGE question: approximate the shape of the curve to quarter circles (1st quadrant, third
quadrant) and determine the time it takes to get to point B.
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