Take two pieces of notebook paper. Wad one up and leave the other unblemished. Release the
one you compressed into a ball and watch it fall. Take two hands and release the other. What was
the first thing you noticed? How much longer did it take the ball of paper to reach the ground
versus the one that floated about before it hit?
In this section, we used coffee filters to study
drag force. You saw in the video how to
analyze a falling object in which drag forces
affect the velocity vs. time curve. Figure 1
illustrates a typical drop. The filters are held
beneath a motion detector. Upon release, the
student’s fingers are not to move, as the
detector will record those motions as well.
Running parallel to the drop axis is a two-meter
stick. The detector is activated, and then the
student drops. The motion is detected until it
reaches the floor.
Fig. 1 A typical student drop of the object
Open up an Excel spreadsheet.
1. Insert a textbox and place it in the upper left corner of the sheet. In the box, list all of the
variables, based on your research with dropping coffee filters (with cone upwards) and
paper at home as well as Figure 1, in performing an experiment measuring the velocity
vs. time curve of dropping a different number of filters (up to four). Again, refer to the
picture. Clearly label the type of variable it is (dependent, independent, controlled,..).
Make sure you neatly label things for
velocity vs. time
clarity and presentation.
2. Insert another textbox. List all random
errors that should be considered when
doing a proper analysis.
3. Insert a final textbox. In this box,
describe your observations when
dropping one or more filters, the paper
ball, and just the paper. Put things in
context with what we have discussed
in this module.
4. Rename the tab, Discussion, and save
Fig. 2 Velocity vs. time graph for various
5. Create a new tab. Name it terminal. Figure masses (number of filters).
2 is the graph for velocity vs. time for 1-5
coffee filters. Notice how the speed
reaches a value that remains approximately the same. For the dark-blue curve, we could
not reach the terminal speed unless we increased the height of the drop (something you
would NOT have done in the lab itself).
6. In Column A1, label it mass (kg). In B1, label it terminal speed (m/s). Expand the column
to show the full label. Place the data from the table below into Columns A and B (starting
from row 2) respectively.
Terminal speed (m/s)
7. Plot terminal speed vs. mass. Label the graph! Cation: When you plot the mass, make
sure it is in SI-base unit of kilograms!
8. Right-click on the data. Select Trendline and chose the power fit. Paste equation (blow up
the font) on the graph. Note the coefficient out-front and the power of the fit.
9. Using a density of air to be 1.21kg/m3, the diameter of the bottom part of the filter as
0.15m (assume circular cross-section), and the power fit of your Trendline equation,
calculate the drag coefficient. Solve for it first (see video) and then plug in the values.
10. Insert a textbox and ADDRESS these question.
a. Based on your list of random errors, are the results for the drag coefficient and power
of the fit reasonable? Explain. Hint: For the coefficient, google drag coefficients and
research off of the internet.
b. Say something about your choice of controlled variable. Why is this critical for this
11. Save the file and upload.
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