Lab Coffee Filters:  terminal velocity

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.

Part 1

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 how high each group of filters is above the ground before they are released.  ALL filters should be released ABOVE 1.0 meter. Record to the nearest 1.0 cm.

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

Part 2

Holder: Experiment with simultaneously releasing the groups containing 2 filter 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 how high each group of filters is above the ground before they are released.  ALL filters should be released ABOVE 1.0 meter. Record to the nearest 1.0 cm.

Recorder: Record your heights in Data Chart #2.  Repeat two more times.  Circle the best trial's results. If all trials seem equivalent, calculate an average value.

Mass.  Mass one filter, two filters and four filters. Do NOT multiply - measure. Record your results in data Chart #3.

Conclusions

1. Freebody diagrams of a falling coffee filter:

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

2. Using the final equation #9 from the accompanying theory discussion and your results in Data Tables #1, #2 and #3, solve for the precision of your experiment.  Provide your answers in Data Chart #4.

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

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4. 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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