Download Analyzing a Dual Fan Carts Motion (Low Tech).

FR943A/B
Analyzing A Dual Fan Cart’s Motion (Low Tech)
In this experiment you use standard lab equipment to determine the relationship between force,
mass, and acceleration.
Materials
(2) Personal Fans
(4) AA Batteries
(2) Styrofoam Cups
Cart (w/ foam board)
Cart Track
Clay
Duct Tape
Stopwatch
Lab Scale/Balance
Meter Stick
Procedure – Measuring Mass, m
Measure the mass (in kg) of your fan cart assembly, m = ______________
Procedure – Measuring Acceleration, a
1. Set up the cart, as shown below. The track should be slightly downhill such that the cart
maintains a constant speed when given a push. The fans should be pointing straight back.
2. Turn on both fans. Measure the time it takes the cart to travel to the other end of the track.
Calculate the cart’s acceleration. Perform three good trials and calculate an average
acceleration, a.
End
d
Trial
Distance
Traveled, d
(m)
Time, t
(s)
1
2

3
Average:
B. Lamore © C3P Reproduction limited to individual classroom use.
a  2d
t2
(m/s2)
FR943A/B
Procedure – Measuring Force, F
Using a blob of clay, place a fan on the lab scale or balance such that the fan is directed straight up.
Measure the mass with the fan on and off.
Clay
109.72g
120.67g
Fan Off
Fan On
Difference in mass with fan 1 on and off: __________kg.
Difference in weight: __________N (Hint: how are mass and weight related?)
How much force does fan 1 produce? ___________
Difference in mass with fan 2 on and off: __________kg.
Difference in weight: __________N (Hint: how are mass and weight related?)
How much force does fan 2 produce? ___________
How much force, F, do both fans produce? _________
Analysis
1. Compare F and the product ma (a is the average a from the table; m is the mass of the cart).
2. Calculate the % difference between F and the product ma. Show all work.
3. Be prepared to discuss your results with other lab groups.
4. After discussing your results, make a conclusion about the relationship between the net force on
an object, the mass of the object, and the acceleration of the object.
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B. Lamore © C3P Reproduction limited to individual classroom use.
FR943A/B
Analyzing A Fan Cart’s Motion (Low Tech)
Teacher’s Notes
This experiment can produce significant errors between F and ma if not performed carefully.
Check the students’ setups after they adjust the track angle so that the cart maintains a constant
velocity along the track when given a nudge. This balances the slowing effects of friction
between the cart and track. Be sure the cart does not accelerate.
Acceleration can be calculated from the equation d = ½at2. This is valid if the cart is initially at
rest. Timing is critical, so make sure students perform three (or more) good trials before they
take their average. Use the full length of the track. Since timing errors occur when starting and
stopping the stopwatch, increasing the time (and distance) the fan cart runs minimizes error.
In order to accurately measure the force produced by the fans each lab group will need an
electronic lab scale or lab balance, such as a triple beam balance. Typically, each fan with fresh
alkaline batteries will have a difference in mass of about 10g = 0.01kg, which is a difference in
weight of 0.1N. This is the force the fan produces.
The measured F should equal the product ma. You will need to openly discuss the results from
all lab groups to be sure the students understand this relationship. This would also be a good
time to discuss possible sources of error, such as friction between the cart and track, non-level
track, fan not pointed straight back, and batteries weakened during lab.
B. Lamore © C3P Reproduction limited to individual classroom use.