PhysicsLAB: Video Lab: Falling Coffee Filters

This lab is based on a Direct Measurement Video called Falling Coffee Filters released on the Science Education Research Center (SERC) website. The copyright for this video belongs to Independent School District 197 in Mendota Heights MN. The project is partially funded by a National Science Foundation Grant (#1245268) awarded in September 2013.

The following lab directions were designed for use in my Honors Physics I class and only represent one method of analyzing the data provided in the video.

Refer to the following information for the next six questions.

In the table provided below, input the mass of each group of coffee filters. Then, starting when the base of each group reaches the 20-cm line, start a stop watch (find it by clicking on the three horizontal lines) and record how much time is needed for the base of the filters to each the 50-cm line, then the time to travel from the 50-cm line to the 80-cm line, and then the time to travel from the 80-cm line to the 110-cm line, and finally the time to travel from the 110-cm line to the 140-cm line.

Group
Mass (g)

Time between
20 and 50-cm

Time between
50 and 80-cm

Time between
80 and 110-cm

Time between
110 and 140

By referring to the time values for the third group, how do you know that the filters were still accelerating during the intervals 20-50 cm and 50-80 cm?

Refer to the following information for the next six questions.

In the next table, calculate the average speed of each group of filters for the final two 30-cm intervals. You should notice that in each row, these are nearly duplicate values. These values represent the terminal velocity of each group. Each group of filters will reach a terminal velocity (speed) when the air resistance encountered by the filters equals the weight of the filters. This is an example of a projectile NOT being in freefall.

average speed 80-110		average speed 110-140	average terminal velocity	(average terminal velocity)²
(cm/sec)		(cm/sec)	(m/sec)	(m/sec)²

What is the acceleration of any group of filters once they reach terminal velocity?

Refer to the following information for the next three questions.

Next plot a graph of (Terminal Velocity)² vs Mass and determine the equation of its line. The slope of your line of best fit will represent the drag constant for any collection of coffee filters which have the same shape and falling through the same density of the air. You may use EXCEL, and include a printout of your data table and graph. Make sure to give your graph a title, as well as label and scale each axis.

What is the slope of your line?

What is the y-axis intercept of your line?

Use the equation of your line to estimate the terminal speed of of an untested group containing 10 filters.