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Unformatted text preview: SCIE 2320 Ball Bearings and Racetracks The purpose of this experiment is to study how various physical laws that we study are demonstrated through
the use of ball bearings traveling on racetracks. For this experiment, you will work in groups as determined by
1. Individually :
There are two tracks (upper and lower) on the apparatus, and two different types of ball bearings which differ in
composition (and mass).
For each combination of ball bearings and tracks predict which ball bearing will reach the end first (before you
test your prediction!).
2. Group Tasks:
A. The length of each track, in cm (we are interested in the length that the ball will roll along the tracks).
B. The height drop of each track from the starting to the lowest point and the height drop to the end point.
Each track housing has marks indicating the two lowest points you need to measure for each track.
C. The time each bearing takes to traverse each track from start to finish in seconds
- use both stopwatches (get 2 readings) to time the travel for each ball four times on each track (a total
of 8 measurements for each ball bearing on each track)
Be sure to define the end point for measurement and timing records.
Compute the average velocity of each bearing on each track in cm/sec based on your recorded values for
distance and the average travel time.
Estimate the final (instantaneous) velocity (the velocity on the level part at the end of track in both cases) of
each ball based on your measurements. Explain how you produced your estimate in the group report. (Hint:
start the slower ball first, then start the faster ball in such a way that the faster one catches up to the slower
one by the time they both reach the end of the track. You will notice something important about their
relative speeds!) The final velocity of the ball on the upper track will be very close to its average velocity,
so you can use this value as the final velocity for this ball. 3. Individually:
Compute the theoretical final velocity of each bearing on each track based on physical laws.
a) We know that the potential energy (Ep) of an object is based on its height … Ep = mg∆h ,
where m = mass, g = 980 cm/sec2, and ∆h is the change in height of the object.
b) We further know that kinetic energy (Ek) of a moving object is based on its mass and velocity … Ek= ½mv2 ,
where m = mass and v2 = velocity squared.
c) We also know that energy is conserved : if an object at height h1 falls some distance to a lower height h2, then
some of the potential energy is converted to kinetic energy (Ek), and this kinetic energy is exactly equal to the
potential energy lost due to the change in height (∆h) of the object (since it is at a lower height) due to the Law
of Conservation of Energy:
Ek gained = ½mv2 = Ep lost = mg∆h
Using this formula, we can compute theoretically the maximum and final velocities of our ball bearings. Just
solve this equation for v: ½mv2 = mg∆h . Note that the mass cancels out! So the velocity of the ball bearing is
independent of its mass!
d) To solve the equation above for v:
½mv2 = mg∆h
1) divide both sides by m, which yields : ½v2 = g∆h
2) multiply both sides by 2 to get rid of the ½, which yields : v2 = 2g∆h
3) take the square root of both sides, which yields v = 2 gΔh 4. Turn in the following :
a) Each group is to submit a completed copy of the datasheet before leaving today. Make certain that all
participants in the group have their names on the datasheet.
b) Each individual will submit a copy of the completed datasheet plus the typed answers to the questions on the
accompanying sheet. This is due one week from today. ...
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