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# Newton's Third Law

## For every action, there is an equal and opposite reaction.

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The Art of Falling

### The Art of Falling

Credit: The U.S. Army
Source: http://www.flickr.com/photos/soldiersmediacenter/2990718614/

After jumping out of a plane that is flying 10,000 ft above the surface of the Earth, this skydiver reached up to 120 mph before deploying their parachute. Within a matter of seconds the increased surface area allows the pair’s velocity to be slowed to a safe velocity for landing. By using Newton’s 2nd law, you can easily calculate what speed this pair landed at.

#### New You Can Use

• Since the early 1100s, people have been using parachutes to skydive. Even though they didn’t know it, they were using the most basic principles of physics. By using a parachute the effective surface area of the falling body is increased allowing for more air to be “caught”.
• Effectively designed parachutes will expose a skydiver to 3-4Gs of negative acceleration when the chute is deployed. This causes the skydiver’s velocity to go from 120 mph to roughly 18 mph in a matter of seconds. With the forces balanced, the skydiver will be able to safely land.

#### Show What You Know?

Using the information provided above, answer the following questions.

1. When the skydiver is falling at a constant velocity after the parachute is open, what is their acceleration?
2. Explain why it is not advised to use a parachute that is a big as possible, assuming you could safely deploy it?
3. At what point in the skydiving experience is the acceleration due to gravity equal to zero?

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Color Highlighted Text Notes

1. [1]^ Credit: The U.S. Army; Source: http://www.flickr.com/photos/soldiersmediacenter/2990718614/; License: CC BY-NC 3.0

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