### Parachutes and Air Resistance (Jessica Goforth)

Title: Parachutes and air resistance

Principle(s) Investigated:
Air resistance and falling objects, free fall, average speed, terminal velocity8.2.a, 8.2.b, 8.2.e

Materials:

Metal washers

Plastic bag

String

Tape

Procedure:

1.    Use 15 cm of string to tie two washers together securely.

2.    One person from each group drop the washers from shoulder height (record distance) and observe their motion. Record the time it takes for the washers to hit the ground after being released.

3.    Cut a 15x15cm square from the plastic bag and use the string and tape to create a parachute for the washers.

4.    Have the same person who dropped the washers earlier hold the washers at shoulder height (same distance) while the other group members hold the parachute open above the washers.

5.    Drop the washers and observe their motion. Record the time it takes for the washers to hit the ground after being released.

6.      Compare your observations between the two trials and think about what caused the differences.

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Student prior knowledge:

-        Air resistance is the force that opposes motion of objects through air

-        Magnitude of air resistance depends on the size, shape and speed

-        Terminal velocity is reached when upward air resistance equals the downward force of gravity.

-        Something is in free fall only if gravity is the only force acting on an object. This can only occur where there is no air present.

Explanation:
Give a thorough explanation of the experiment or demonstration. Your explanation should be written to give your fellow teachers a solid understanding and include greater detail than what you might provide for your secondary students. Make certain to include equations whenever pertinent.

1.    How did the motion of the washers differ between the two trials?

2.    What forces were acting on the washers and the parachute during the two trials?

3.    Were the forces on the washers balanced or unbalanced? How do you know?

4.    During which trial was the force of air resistance greater? Explain.

Applications to Everyday Life:
The terminal velocity of hailstones is between 5 and 40 m/s- if there were no air resistance the hailstones would reach velocities near 350 m/s!

Skydivers count on air resistance against their parachutes to slow them down before they reach the ground.

Photographs:
Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.

Videos: Include links to videos posted on the web that relate to your activity. These can be videos you have made or ones others have made.