Electrical Interactions

     The first experiment we conducted on Monday involved the electrostatic forces between two pieces of scotch tape. We first had to place two 10cm strips of scotch tape onto the table with the sticky side down. We then peeled the tape off of the table and brought the non-sticky sides of the tape toward each other and observed what happened. This observation is the statement labeled A in the picture. Then, we placed two strips of tape on the table with the sticky side down and placed another strip of tape onto each of the strips on the table. They were labeled "B" for bottom and "T" for top. We then pulled the tape off of the table, separated the tape that was joined together, and answered some questions about the interactions between each of the strips. The answers to these questions are labeled 1, 2, 3, and C.

     The next experiment we engaged in was an Electric Force Law Video Analysis Activity. The first thing we did was derive an expression for an electric force acting on a hanging ball. This derivation can be seen above. We then had to do the actual video analysis and plot a graph of electric force vs. separation distance.

     This is a picture of the graph we obtained from Logger Pro. In order to construct this graph we had to set the origin at the middle of the hanging ball, click the Add Point button, and click on the middle of the ball on the stick as each frame progressed until the video ended. We then had to select the Set Active Point button, select Add Point series, and perform the same process with the hanging ball until the video ended. Then we had to create two calculated columns called the Separation Distance (distance between the two balls) and Electric Force, which was done by entering our previously derived equation. The result was the graph seen above.

     Finally, we had to answer some questions about the results we got from the experiment. The first question asked if we were able to show that electric force was inversely proportional to the square of the distance between the two charged balls in the video. The second question asked for our percent difference for our experimental value for the exponent of 2.194 with the actual value of 2 for this law. This question also asked us to determine the charge on each ball if we assumed the charge on each ball was the same and if the charge on one ball was half of that of the other. We had to use one of our data points to answer these two questions. The third question asked if we were able to determine the sign of the charge on each ball from the experiment. Finally, we were asked about sources of uncertainty in our data. We cannot tell how accurately the mass of the ball and the length of the string were measured because they were given, but how accurately we clicked on the center of each ball at each frame certainly led to some source of uncertainty.