Net Force Lab

Net Force



To investigate forces, computer programs, and mapping software used in physics by measuring the acceleration of a rubber band powered car and calculating the maximum net force produced when gradually increasing the mass of the car.


There were three different hypotheses. One group hypothesized that the maximum net force would decrease when more weight was added. Another hypothesized that net force would increase to a point and then decrease once too much weight was added. And the final hypothesized that the net force would remain unchanged.


-Rubber Band Car

-Motion detector


-SPARKvue Software

-Graphing Software

-Gram weights (10 to 200 grams)

-Triple-beam balance


Setup motion detector and SPARKvue software to record velocity and acceleration of a moving object

Measure winding distance 2 feet from the motion detector

Wind car from 2 feet

Begin recording data in SPARKvue

Release car

Do 2 trials and increase weight by 5, 10, or 50 grams

Repeat until 200 grams has been added


Run # Force (N)

1 0.2016
2 0.2664
3 0.2132
4 0.2624
5 0.2132
6 0.1479
7 0.2349
8 0.2208
9 0.2576
10 0.2522
11 0.3104
12 0.2754
13 0.2142
14 0.3024
15 0.28
16 0.305
17 0.2684
18 0.2772
19 0.2772
20 0.2982


Our results show a subtle and somewhat erratic increase in net force as more weight is added. From this we can conclude that net force increased as we added weight; however, we can’t be sure the maximum force was achieved because there was no definite decrease in net force. Errors could have resulted from interference of motion detector from hands, echoes, or other sound interference; the vehicle may not have been perfectly aligned with motion detector path; the motion detector cycled at only 10 hertz and was set at the “large-object” setting—greater accuracy could have been obtained by using a higher cycle rate and the “small-object” setting on the motion detector; rubber-band fatigue could have been a factor in later trials; and wheels may have become out of alignment. If this experiment is done again we would use a more controlled environment with less interference, use the “small-object” setting on the motion detector, use a more stable and solidly built car, and use a higher cycle rate on the motion detector.


The 8th Grade Class of AIS

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