Lab Falling Coffee Filters
Background Information: The amount of air resistance an object encounters is directly proportional to its surface area and velocity. Terminal velocity, vt, is achieved when the air resistance equals the object's weight and the object can no longer accelerate. It reaches a state of dynamic equilibrium.

Experimental Procedure/Data: Each group needs three members: holder, measurer, recorder. Each group needs three stacks of filters (1 filter, 2 filters, 4 filters) and two meter sticks.

The purpose of the lab is to discover the release height for each group of filters that will enable two groups, which have reached terminal velocity, to reach the floor at the same time.

Data Table I: 2 filters

Holder: Experiment with simultaneously releasing the groups containing 1 filter and 2 filters to determine a best estimate for the appropriate release heights that allow the two groups to strike the ground simultaneously. When ready, hold each group steady so that their distance above the ground can be measured. Make sure that the flat side is facing the ground.

Measurer: Measure the mass of each group of filters. Do NOT multiply the total by the mass of one filter - MEASURE each group and record your information in the data table provided below. Then measure how high each group of filters is above the ground just as they are released. ALL filters should be released AT OR ABOVE 1.5 meter. Record to the nearest 1.0 cm.

Recorder: Record your heights in Data Chart #1. Repeat two more times. Input the best trial's results in the final column. If all trials seem equivalent, calculate an average value.

 Data Table I trial 1 trial 2 trial 3 best results number height (m) height (m) height (m) height (m)
 one filter
 two filters

Data Table II: 4 filters

Holder: Experiment with simultaneously releasing the groups containing 2 filters and 4 filters to determine a best estimate for the appropriate release heights that allow the two groups to strike the ground simultaneously. When ready, hold each group steady so that their distance above the ground can be measured. Make sure that the flat side is facing the ground.

Measurer: Measure the mass of each group of filters. Do NOT multiply the total by the mass of one filter - MEASURE each group and record your information in the data table provided below. Then measure how high each group of filters is above the ground just as they are released. ALL filters should be released AT OR ABOVE 1.5 meter. Record to the nearest 1.0 cm.

Recorder: Record your heights in Data Chart #1. Repeat two more times. Input the best trial's results in the final column. If all trials seem equivalent, calculate an average value.

 Data Table II trial 1 trial 2 trial 3 best results number height (m) height (m) height (m) height (m)
 two filters
 four filters

Data Table III: Mass Data

Measurer: Measure the mass of each group of filters. Do NOT multiply the total by the mass of one filter - MEASURE each group and record your information in the data table provided below.

 number of mass filters (kg)
 one filter
 two filters
 four filters

Conclusions

Answer the following questions using the information from Data Tables #1, #2 and #3, and the accompanying resource lessons on air resistance and terminal velocity.

Refer to the following information for the next three questions.

Freebody diagrams of a falling coffee filter:

 A B C D E

... when first released, v = 0
... after falling a short time, v is small
... after reaching terminal velocity, v = vt

 Part I Part II
 % difference

 Since one set of data produced a better result that the other, postulate on what conditions may have produced the poorer result.

 Describe how the filters "behaved" when they were moving at terminal velocity so that someone who was not present during the experiment could use filters "at home" to see the same phenomena.

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