Air Resistance

EdPuzzle on GC

Experimentation

Choose which experiment you will be conducting:
1. How does mass affect the terminal velocity of an object?
  1. Choose a single liner, shape the liner so that it falls straight down.
  2. Measure its effective diameter as it falls using a ruler.
  3. Calculate the cross-sectional surface area of the liner.
  4. Measure the mass of the liner using an electronic scale.
2. How does the surface area affect the terminal velocity of an object?
  1. From the given piece of foil, create a 'boat' that will fall in a straight line (straight down).
  2. Measure the mass of the foil boat using an electronic scale.
  3. Measure the dimensions of the foil boat using a ruler.
  4. Calculate the cross-sectional area of the foil boat.
Hold the object just below the motion detector.
Start the data collection on the LabQuest and release the object.
From either the position-time graph or the velocity-time graph, determine the terminal velocity of object.
Take repeat readings until you have consistent data.
Repeat the investigation with multiple liners (measureing the mass each time) or change the cross-sectional area of the foil boat (measuring the area each time).

From one velocity-time graph, select 3 important moments in the graph
1. Explain why you chose these 3 important moments.
2. Draw a free body diagrams for each of the moments selected, use F_D for the force of drag.
3. Using the equation to the right, derive an equation to describe the acceleration of the coffee filter at each of the moments.
Create a graph of your raw data (terminal velocity v. mass).
Describe the relationship between terminal velocity and the mass of the coffee filters. How does increasing the number of filters (and thus the mass) affect the terminal velocity? Provide an explanation based on forces and acceleration.
Compare your experimental data on terminal velocity with a theoretical model that assumes constant drag coefficient b.
1. Does the experimental data closely align with the model?
2. The b coefficient is dependent upon several constant variables describing both the falling object and 'fluid' the object is fall through. Describe which variables of the object and fluid may also be included in determining the b coefficient.
3. Discuss possible sources of deviation, including assumptions made in the model and experimental limitations.
Critique the methodology used in this experiment to measure terminal velocity. Suggest two improvements to increase the precision or accuracy of your data, and explain why these adjustments would make the experiment more reliable.

The resultant force F on a raindrop of mass m falling vertically with velocity v is given by the equation:

where k is a constant and g is the acceleration of free fall.

The falling raindrop eventually reaches a constant (terminal) velocity.

Which graph shows the variation of the terminal velocity of the raindrop with mass m?

A ✓

Using the graph at the right, answer the following questions.

Look at the initial part of the graph, where speed increases from zero. What forces are acting on the parachutist in this phase? Why isn’t the speed constant from the start?
Identify the section of the graph where the speed becomes constant.
1. What does this constant speed indicate about the forces acting on the parachutist at this point?
2. How could the parachutist control this speed?
When the parachute opens, what happens to the speed? Explain why the speed changes in this way and identify the forces involved.
After the parachute deploys, the speed levels off again but at a lower value. Why does the parachutist reach a new, lower terminal velocity instead of continuing to slow down to zero?
Describe the motion of the parachutist in the first part of the graph (before the parachute opens). Is the parachutist in free fall? Explain your answer based on the graph.
What does the slope of the graph indicate at different stages of the descent? How would the slope change if the parachutist were heavier but had the same parachute?
In question 4.2 from the coffee filters experiment at the top of the page, which of the variables identified in the coefficient b change between the points 'C' and 'E' on the graph?

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