Tamara- AP Physics

Centipetal Force Lab


The purpose is to find the relationship between Centripetal Force and Tangential velocity.  WE have to graph the data we collect and determine a mathematical model that describes the relationship. 
- String
- Stopper
- hollow tube
- stop watch- computer
- steel washer
- meter stick
Factors to Consider:

-  What data should you collect ? We should record the weight of each end of our mechanism and the radius before any testing. While experiment we should record the time of ten revolutions in many different trials.
-  Which variables should be graphed in order to establish the mathematical model? Force versus time.
-  After graphing the variables, how will you establish a relationship? We will look for the best fit curve for the points given. Some points may need to be taken out due to human error.
-  How will you test the validity of your mathematical model? In the computer graphing program that we have, we are able to set a curve through the points to make sure that the data we found was accurate.

We were given a few pieces of equipment. We started by massing these items and recording our findings.  We, then, began to construct our device by attaching the stopper to the string with a bowline knot.  We put the string through the hollow tube and attached the washer to this end of the string.  Then, we had to measure the string (radius) to equal 50 cm, which was the required length.  Next, we had someone swing the rubber stopper end over their head horizontally.  When the washer became stationary, we timed 10 revolutions.  The 10 revolution allows for a more accurate calculation of one revolution.  We recorded our data while we were experimenting. 


Stopper: 20.1 grams

Weights + mini-stopper: 32.3 grams

Horizontal revolutions (10 revolutions):
                                                 7.2 s
                                                 7.3 s
                                                 7.78 s

Failed data revolutions (10 revolutions):
                                                  8.40 s
                                                 8.282 s

Radius: 50 cm
Data Analysis

The graph below shows the best fit curve for the class data that was usable.  The best fit line/curve is a quadratic equation. 


Centripetal force and tangential velocity have a quadratic relationship.  There are many sources of error in this experiment.  It is impossible to keep the radius at exactly 50 cm with the equipment given.  Also, our group found it difficult to keep the string horizontal for a particular amount of time, it always seemed to be a little low.  Each group had a different technique and chose to use different measurements.  This allows for more possible error mistakes.  Human error was very prominent.  We found a calculation error for one group, but that is not uncommon.  Nonetheless, we concluded that there is a quadratic relationship between centripetal force and tangential velocity.