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Coffee Filter Air Resistance Lab

Instructor: Amanda Robb
In this lab you'll be learning about falling objects in our atmosphere. By studying the terminal velocity of coffee filters with different masses, you'll be able to understand the relationship between mass and air resistance, as well as the time it takes for objects to fall.

Introduction

Research question: How does mass affect air resistance?
Age: High school and up
Safety concerns: None
Time: 3 hours
Independent variable: mass
Dependent variable: terminal velocity and air resistance
Control variables: Type of coffee filter

Picture dropping two objects out the window: something heavy, like a bowling ball, and something light, like a feather. Which one hits the ground first? You're probably imagining the bowling ball smashing into the lawn and the feather still near the window. So, why do heavier objects fall faster?

To investigate this phenomenon, we'll be dropping coffee filters with different masses and measuring the terminal velocity, when the velocity of a falling object becomes constant and the forces are balanced. With this information we can understand the relationship between air resistance and mass. If you need a refresher on balanced forces, check out this lesson:

Balanced Forces: Definition and Examples

Before you start, consider this question: How will mass affect air resistance and terminal velocity?

Materials

  • Electronic device with video capability
  • 5 coffee filters
  • Small scale
  • Notebook
  • Masking tape
  • Three meter sticks
  • Data table 1:

Time (seconds - s) Position(meters - m) Velocity (meters per second m/s)
2
4
6
8
10
12
14
16
18
20
  • Data table 2:

Mass of coffee filters (kilograms - kg) Terminal velocity (m/s) Air resistance (Newtons - N)





Steps

1. First, measure the mass of each coffee filter in kilograms and record this in data table 2. If your scale measures in grams, divide that number by 1,000 to get kilograms.

2. Next, get one coffee filter and find a location to drop it from 3m high with a wall behind you. Tape three meter sticks end-to-end on the wall so you can record the position from the video. Hold the coffee filter so the edge is exactly at the 3m mark. Drop your coffee filter while recording the video.

2. Now, examine your video. For every 2 seconds, record the position of the coffee filter in data table 1. Divide position by time to get the velocity at each time interval.

3. Create a graph of velocity versus time. Terminal velocity occurs when velocity stops changing, so when the slope of the line is flat, that is the terminal velocity.

Terminal velocity occurs when velocity no longer changes
v versus t

4. Repeat steps 1-3 for each set of coffee filters.

5. Now, analyze your data and calculate air resistance for each set of coffee filters. When terminal velocity is reached, velocity is constant. Since acceleration is a change in velocity, if velocity is constant there is no acceleration.

If there is no acceleration, the forces acting on the object must be balanced. For our coffee filter, the only two forces acting on it are the force due to gravity, pulling it down, and air resistance, pushing it up. If these forces are balanced, they must be equal.

So, we can solve for the air resistance by calculating force due to gravity, which is the mass of the object multiplied by acceleration due to gravity, or 10 m/s2.

Force due to gravity is equal to air resistance at terminal velocity
equation

Record the air resistance for each set of coffee filters in data table 2.

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