Activity: Terminal velocity

Purpose

1) To determine the terminal velocity of a coffee filter as it falls near Earth's surface by applying Newton's laws of motion.

2) How does the weight of an object affect its terminal velocity?

 

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Discussion:

The terminal velocity of a falling body occurs during free fall when a falling body experiences zero acceleration. This is the result of two separate forces acting on the falling body, gravitational force downward and air resistance upward, that are equal in magnitude but opposite direction. This results in a net force of zero on the falling body and therefore an acceleration of zero.

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Equipment:

several paper coffee filters

stopwatch

triple beam balance

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Procedure:

Determine the mass of the paper coffee filter and calculate its weight.

• You will drop filter(s) from the ceiling and time their fall.
• Measure d and t Make a data table for a range of filters.

  # filters	trial 1	trial 2	trial 3	Avg. time	distance	Terminal velocity
  1
  5
  10

• Find v for each trial this is the terminal velocity. (Show one example.)
• Calculate the forces acting on the filter when it is at terminal velocity, using f_net = mass*a

Analysis:

• Your group needs to figure out how to find the terminal velocity
• Draw a free body diagram of when the filter is accelerating .
• Show calculation of terminal velocity.
• Measure the mass of the filter.
• Find the force drag (air resistance) by...
  • Draw a free body diagram of when the filter is at terminal velocity and discuss unbalance/balanced forces, force_net and acceleration for each.
  • Before you calculate the force convert [grams] to [kilograms] then your units will work out to [Newton's]
  • So; ^- F_g = F_drag
  • f_g = m* ^-g
• Discuss:
• unbalance/balanced forces, force_net and acceleration when filter is accelerating.
• unbalance/balanced forces, force_net and acceleration when filter is at terminal velocity.
• Question: What does this tell us about the force of air resistance on a jetliner moving at a constant velocity?
• Question: Why is v_avg the terminal velocity? That is, how would you use a free body diagram to support v_avg as the terminal velocity.
• Question: If the filters are no longer accelerating and the total forces acting on the them f_net is zero, why do they keep moving?
• Question: Explain why your group calculated the terminal velocity the way it did.
• Question: How does the mass of the falling object affect the terminal velocity?
• Question: How is "terminal velocity" a misnomer?

Last modified: 18-Nov-2008