Name _________________________________
Physics Day Pre-Lab: Free Fall
Background: http://www.learner.org/exhibits/parkphysics/glossary.html
Galileo first introduced the concept of free fall. His classic experiments led to the
finding that all objects free fall at the same rate, regardless of their mass. According to
legend, Galileo dropped balls of different mass from the Leaning Tower of Pisa to help
support his ideas.
A freely falling body is an object that is moving under the influence of gravity only.
These objects have a downward acceleration toward the center of the earth. Newton later
took Galileo's ideas about mechanics and formalized them into his laws of motion.
How do free-fall rides work? Free-fall rides are really made up of three distinct parts:
the ride to the top, the momentary suspension, and the downward plunge. In the first
part of the ride, force is applied to the car to lift it to the top of the free-fall tower. The
amount of force that must be applied depends on the mass of the car and its passengers. Motors apply this force, and there
is a built-in safety allowance for variations in the mass of the riders. After a brief period in which the riders are suspended
in the air, the car suddenly drops and begins to accelerate toward the ground under the influence of the earth's gravity. The
plunge seems dramatic. Just as Galileo and Newton explain in their theories of free fall, the least massive and most
massive riders fall to the earth with the same rate of acceleration. If the riders were allowed to hit the earth at that speed,
coming to a sudden stop at the end of the ride, there would certainly be serious injuries. Ride designers account for this by
building an exit track. The car is attached to this track, which gradually curves toward the ground. A stretch of straight
track allows the car to slow down and brake, producing a controlled stop at the bottom, which keeps passengers from
getting injured.
The free fall ride at Great Adventure was removed before the 2007 season, but we have preserved a video record of its
operation here: http://resources.physicsygoodness.com/assets/free_fall.mov
Measurement
Make the following time measurements from the video: (1) for the elevator going from the ground to the top, (2) for the
free fall from the top to just before the track starts to curve, and (3) for stopping, while the car is traveling horizontally.
Obtain times from two other students, and average the results.
Section of Ride
Measured Times
Average
Elevator Going Up
tup =
Region A – Free Fall
tA =
Region C – Stopping Track
tC =
Calculations
Physics day lab answers will be submitted online at: http://students.physicsygoodness.com
Your teacher will provide instructions on how to log in.
Every student has been assigned a mass to use for Physics Day calculations. After you log in, this mass is printed after
your name in the website banner. Obtain this mass and use it for all calculations.
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Getting to the Top - Power
W = Fd
P=
W
t
1. Find the work done in lifting you to the top. The average
lifting force is the upward force needed to lift your weight.
The full distance from the ground to the top is 30 m.
W = ________ J
2. Find the power used getting you to the top.
P = _________ W
Coming Down – Checking the Free Fall
d = vi t +
1 2
at
2
3. Calculate the time it should take for the free fall drop of
14 m (region A) if the track were frictionless.
4. Calculate the percent error for the time of free fall you
measured with the accepted time you calculated above.
t = _________ s
% err = _______ %
Coming Down – The SPEED in the Curve
2
2
v f = vi + 2ad
5. Calculate the instantaneous speed after a drop of 20
meters assuming the ride is frictionless. Without friction,
the curved track changes the direction of the car without
affecting the speed.
vf = _________ m/s
Coming Down – The FORCE in the Curve
Fc =
mv 2
r
6. The 20 meter point is the curve which has a radius of 15
m. Calculate the centripetal force needed to make you
follow the curve of the ride at this point.
Fc = _________ N
ff =
Fc
Fg
7. Calculate the force factor experienced at this point.
ff = _________
Stopping – Momentum and Impulse
8. The drop to the start of the braking track is 25 meters.
Find the speed assuming all of the potential energy lost
becomes kinetic energy.
v = _________ m/s
p = mv
9. Calculate your momentum (pi) as you enter the stopping
track.
pi = _________ kg m/s
Ft = mΔv
10. Your momentum after stopping, (pf) is 0. Use the
concepts of impulse and momentum to calculate the average
force on you while stopping. You measured the time used to
stop the car.
F = _________ N
11. Relate the braking force to your normal weight by
finding the force factor.
ff = _________
ΔE p = ΔEk
mgΔh =
ff =
1 2
mv
2
brakeforce
Fg
After you have completed the above work, log in and enter your answers on the Physics Day website.
Questions
Log in and answer the web-based questions for this lab, to be found under “verbal responses.” Also, submit your
measurements and calculations.
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