Activity: Calculating the Drag Coefficient of a "Sawed-Off" Cone
You will need:
- three coffee filters
- balance or scale
- meter stick
- stop-watch
- calculator
Procedure:
In this activity, we will be testing some of the variables that affect the drag force of a falling object: a coffee filter. Using our data, we will be able to calculate its drag coefficient.
Step 1: Divide yourselves into groups of two. Each group will need a meter stick, a stopwatch, and 3 coffee filters.
Step 2: Measure the filter to find its area. Which area do you measure, the smaller circle at the bottom of the filter or the larger one? Why?
Step 3: Using the meter stick as a guide, hold one filter at a height of 1.0m. One partner will drop the coffee filter while the other partner times how long it takes the filter to drop to the floor. Repeat 5 times and find the average time.
Step 4: Use this data to calculate the drag coefficient of a “sawed off” cone.
Step 5: Repeat with 2 and 3 filters and fill in the table below. Show that the drag coefficient is constant.
ρ(air) = 1.275 kg/m3
Assume all filters are the same size and mass.
For each mass, calculate the average speed of the falling filter. Assume this is the terminal velocity.
Use this velocity to calculate the drag force acting on the object and, consequently, the drag coefficient of this shape.
Repeat with all three masses to verify that the drag coefficient is a constant for this shape.
What are the possible sources of error? Think about some approximations and assumptions we made and how they will affect the final answer. Is your final answer higher or lower than expected? By how much?