Drag Force on a Coffee Filter

Introduction:
This lab studies the relationship between air drag force and the velocity of a falling body. It also looks into the velocity dependence of the drag force. The drag is created in the opposite direction of the objects motion. Using a motion sensor and the graphing software we can gather the terminal velocities from the graphs generated by Logger Pro.

Procedure:
1.  Gather nine coffee filters, and make sure the shape stays the same. If the shape is altered for some it will create more/less surface area than others, compromising the results. Place the motion detector on the floor facing upward and hold the nine filters 1.5 m above the sensor. Drop the filters to collect the data and a graph will be shown with a constant decreasing slope. As the time increases the position decreases because the filters are falling from 1.5 m to 0 m. On the graph select the portion where the graph shows the constant speed.

2.  The portion of the graph that was selected can be analyzed by selecting curve fit. Linear curve is the shape of the graph and once selected it gives you the slope. Record the slope because it represents the average velocity of the falling filters. Repeat the steps but every 4 trials remove one filter. Table 1.1 displays the slopes and average slope of each coffee filter trial.

3. Curve fit the linear graph. The slope of this line represents the terminal velocity.

4. How does your value of n compare with the value given in the text? what does the other fit parameter represent? Our n value equal 1.9, the book's value is 2. This value represents the cross section of the air filters. 


Table 1.1

Note: unit mesurement of m/s for the trials and average.

5. Make a graph that plots packet weight vs terminal speed. Perform a power fit to the data and record the power n given by the computer. Check the percent error between your n and the theoretical n. Table 1.2 shows the graph of number of filters vs terminal speed.


 Table 1.2

                     

               filters vs terminal speed

Conclusion:

This lab helped explain that the drag force on a falling object eventually equals the magnitude of the gravity force with an Fnet of 0. At this point there is no further acceleration and the object falls at a constant speed. Once this object reaches the terminal speed it will continue to fall constantly until it hits the ground or another external force is applied.The most common sources of error that we came across was that if there's and object or movement near the motion detector it can compromise the results.