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I find it totally non-intuitive that a parachute would jump back a little when deployed. I am not talking about the effect as seen by other watchers. Is it possible that some air is compressed under the chute such that it causes that small bounce back?

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  • $\begingroup$ Have you a link to a video which shows this? $\endgroup$ – Farcher Apr 14 '17 at 20:14
  • $\begingroup$ Actualy myth 3 (here)[google.cz/amp/listverse.com/2009/02/05/… $\endgroup$ – Zveratko Apr 14 '17 at 20:17
  • $\begingroup$ But I believe it happens maybe on smaller scale $\endgroup$ – Zveratko Apr 14 '17 at 20:18
  • $\begingroup$ The lines that connects the diver to the chute are elastic to absorb shock. So when the chute catches the air there is an initial stretch in the lines followed by elastic recoil - a movement of the diver backward relative to the chute - but each object never continues to move downward. Is that what you mean? $\endgroup$ – docscience Apr 14 '17 at 23:11
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If you're asking what I think you're asking, then your answer lies within the falling of the person. When someone is falling through the air, the wind is rushing up relative to the person because the person is moving down relative to the air. In other words, what causes the "blowback" is the drag force suddenly increasing many times over. Drag is the force something (or someone) experiences when trying to move in a fluid. It can be said to be a complicated type of friction.

In this case, a parachute works by drastically increasing the amount of air a person has to push out of the way to move in it. That increase is due to a few things but mostly it's the increase in cross-sectional area and changing of the drag coefficient of our object (in this case our skydiver and parachute).

If you're asking about myth number 8 in your link, I believe the effect your link describes is the relative "going up" of someone who has deployed a chute as seen by someone who has not yet deployed their chute. This is merely due to the sudden change of velocity of the person who deployed the chute.

Think of it this way; the two people skydiving are two drivers accelerating side by side towards something. One of them brakes, hard. The other driver who is still going at the original high speed sees the car next to him "bounce back" but to someone standing still looking at both of them, the car just slowed down, it didn't go backwards. Similarly, the parachute deployer only slows down, he/she doesn't go up. It only looks that way to the other person falling down.

Edit: To answer your comment's follow-up, no. This is because of Newton's laws. In much the same way that you can't pull yourself up by your own bootstraps, you can't fall fast enough or deploy a parachute immediately enough for the air to do that (assuming the air is static). The compression of air is due to gravity and the going up that you ask about fights gravity. There is no way to obtain a bigger force going up from a force going down, no matter how compressed the air. It's like if you had a weight on top of a spring and tried to make it bounce higher than its release point, it's not going to happen. It may happen in real life but if it did, then it's because of air currents.

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  • $\begingroup$ Will the 'blowback' rise for any moment the chute up? Immediate opening the shute will cause air compresion which will create the minimal up movement? $\endgroup$ – Zveratko Apr 14 '17 at 20:29
  • $\begingroup$ I have edited my answer to address your comment. $\endgroup$ – HsMjstyMstdn Apr 14 '17 at 20:38
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    $\begingroup$ To continue with the car analogy; you can't brake so hard that you go backwards. $\endgroup$ – HsMjstyMstdn Apr 14 '17 at 20:42
  • $\begingroup$ When you full stop the torsion force of car rims will allow for small play(causing you to go forth and then back) $\endgroup$ – Zveratko Apr 14 '17 at 20:45
  • $\begingroup$ What you are referring to is mainly due to all the springy-bits in a car bouncing back and playing "catch-up" to the wheels that have already stopped. The car leans slightly forward in a braking state and bounces back to normal after the car has effectively stopped. What you are experiencing is real but there will never be enough bounce back to move the car backwards. If there were, I could theoretically drive my car backwards simply by going forwards and then braking hard enough. $\endgroup$ – HsMjstyMstdn Apr 14 '17 at 20:49

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