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Name:_____________________________
duty: timer dropper pusher measurer
Car Push Lab
Purpose: Apply Newton’s second law to find the mass of a vehicle.
Materials:
Automobile
Measurement devices (tape measure)
Marking devices (balloons/w sand, blocks of wood, etc.)
Stopwatch
Bathroom Scale (calibrated in Newtons)
Discussion: Newton was the first to realize that the acceleration produced when we move something depends
not only on how hard we push or pull, but also on the object’s mass. He devised one of the most important rules
of nature ever proposed, his second law of motion His second law of motion states:
The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to
its mass. The direction of the acceleration is in the direction of the applied net force.
We use SI units such as m/s2 for acceleration, Newtons (N) for force, and kilograms (kg) for mass.
Many people intuitively know that the larger an object is, the more difficult it is to get moving. Very few people
realize that Newton’s 2nd law is great for calculating how much force is required to accelerate a massive object
over some distance. You will use your knowledge of Newton’s 2nd law to accelerate an object with a constant
force and determine the mass of an automobile.
Procedure:
1. Take a car, set it in neutral and set the emergency brake. Your group will be arranged with two people
for measuring crew duties, 1 timer, 1 dropper, and 1 pusher.
2.
Initially you will need two people in the car. One of these individuals will call out regular time
intervals (2 sec) for which the second person will drop objects outside the car to demarcate its position
in time and space. It is critical this ‘dropper’ has placed a mark at t=0 sec. The timer must coordinate
with the pusher outside the car as when to begin applying force.
3.
The pusher will use Newton’s bathroom scale and gently place it on the rear of the vehicle, being
careful as not to mark the delicate paint job of the car. This person is advised to start very slowly, and
push with a constant force (between 100-150N). Be sure to let other students in class know what net
force you have exerted upon the car to accelerate it.
4.
The measuring crew must take measuring devices and record the distance between marks. After you
have measured all the position intervals, pick up the objects and share your measurements with the rest
of the class.
5.
Record the data obtained from the 3-4 groups in class. Calculate the velocity over each time interval,
plot a velocity versus time graph for each trial, and find the acceleration for each trial.
6.
Once you have found the acceleration and force for each trial calculate the mass of the vehicle.
7.
Find the actual mass of the vehicle a reported in the car owners manual or driver’s side door.
Name:_____________________________
duty: timer dropper pusher measurer
Trial one-
net force_________N
acceleration= ____________m/s2
net force_________N
acceleration= ____________m/s2
net force_________N
acceleration= ____________m/s2
net force_________N
acceleration= ____________m/s2
Elapsed
Time (s)
Dist.
Between (m)
Time interval
(s)
Velocity
(m/s)
Trial twoElapsed
Time (s)
Dist.
Between (m)
Time interval
(s)
Velocity
(m/s)
Trial threeElapsed
Time (s)
Dist.
Between (m)
Time interval
(s)
Velocity
(m/s)
Trial fourElapsed
Time (s)
Dist.
Between (m)
Time interval
(s)
Velocity
(m/s)
Actual mass of the vehicle:_____________lbs ________________kg
Questions:
1.
What was the average mass (in kilograms and lbs- 1 kg = 2.24 lbs) of the vehicle? Each trial may have
a different value, be sure to report all those which your class attempted. What is the actual mass of the
vehicle?
2.
How does this average value compare to the reported mass of the vehicle? How close did you arrive in
percentage terms?
3.
Describe any errors you believe there may be in this method of determining a car’s mass.