- #1
DocZaius
- 365
- 11
I was thinking of the free body diagram of a skydiver and came across something which bothered me.
Fg = Force of gravity
Ff = Force of air friction
1. The skydiver jumps out. Fg (constant) pulls down and Ff increases until terminal velocity is reached. At that point, the skydiver is falling at a constant speed and Ff = -Fg
2. The skydiver opens his parachute. Momentarily, Ff is greater in magnitude than Fg and the skydiver accelerates upwards, losing some of his falling speed until a new terminal velocity is reached.
3. The skydiver is now falling at a constant speed but with a different profile. But since he's falling at a constant speed, Ff = -Fg.
Since Fg is constant, that means step 1 and step 3's Ff's are identical. But why is the force of air friction not higher with the parachute open?
I am sure I am missing some stupid obvious thing.
edited to add: I think I figured it out. After the parachute has opened, even though there are more air molecules hitting the skydiver and parachute, they are doing so at a smaller speed, thus exerting the same total force as pre-parachute. I had erroneously gone through life thinking air friction post-chute-opening was greater. By the way, please let me know if this explanation is correct. Thanks!
Fg = Force of gravity
Ff = Force of air friction
1. The skydiver jumps out. Fg (constant) pulls down and Ff increases until terminal velocity is reached. At that point, the skydiver is falling at a constant speed and Ff = -Fg
2. The skydiver opens his parachute. Momentarily, Ff is greater in magnitude than Fg and the skydiver accelerates upwards, losing some of his falling speed until a new terminal velocity is reached.
3. The skydiver is now falling at a constant speed but with a different profile. But since he's falling at a constant speed, Ff = -Fg.
Since Fg is constant, that means step 1 and step 3's Ff's are identical. But why is the force of air friction not higher with the parachute open?
I am sure I am missing some stupid obvious thing.
edited to add: I think I figured it out. After the parachute has opened, even though there are more air molecules hitting the skydiver and parachute, they are doing so at a smaller speed, thus exerting the same total force as pre-parachute. I had erroneously gone through life thinking air friction post-chute-opening was greater. By the way, please let me know if this explanation is correct. Thanks!
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