Airbag jumping off the ground

  • Thread starter Urpoz
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  • #1
Urpoz
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Let me explain: In the Finnish forum for extremely stupid people like myself, I stumbled on this kind of silly dilemma: You have an airbag, and you put it on the ground, airbag pointing upwards. When you detonate it, it will jump up and fly. What force make it jump? Is it that expanding bag which is dragging itself off the ground, gas from the explosion, opposite force of explosion towards the ground, or something completely different?
 

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  • #2
hilbert2
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The upwards force in this situation is the support force that prevents it from sinking in the ground.

Edit: in the unedited post, I said that a recoil force like with a rocket can be possible if the gases expand unsymmetrically, but this is probably not correct because the bag is a closed system.
 
  • #3
Borek
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Would you expect it to move if it was detonated while hanging on the line? How do these scenarios differ?

Also, it is not different from inflating a mattress or anything else lying on the ground. Just faster, so the effect is more prominent and spectacular.
 
  • #4
DrClaude
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It lifts itself up by pushing on the ground, the same as when you jump.
 
  • #5
berkeman
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Another way to see the same thing -- compress a spring and tie a string around it so it stays compressed. Set it on the ground with the spring axis pointing up. Cut the string with a pair of scissors, and the spring jumps into the air. It's the rapid expansion to a larger size that generates the force to make the spring jump up. :smile:
 
  • #6
A.T.
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Let me explain: In the Finnish forum for extremely stupid people like myself, I stumbled on this kind of silly dilemma: You have an airbag, and you put it on the ground, airbag pointing upwards. When you detonate it, it will jump up and fly. What force make it jump? Is it that expanding bag which is dragging itself off the ground, gas from the explosion, opposite force of explosion towards the ground, or something completely different?
Are you familiar with pop corn?
 

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