Physics of a Merry-go-round

Discussion in 'Physics & Math' started by Boris2, Apr 19, 2013.

  1. Boris2 Valued Senior Member

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    Is there anything wrong with the physics of this GIF?
     
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  3. Russ_Watters Not a Trump supporter... Valued Senior Member

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    Yeah, blue dude is aiming his gun at the guy in the center, so he shouldn't be hitting him.
     
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  5. John Connellan Valued Senior Member

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    They are very slow moving bullets! (or an extremely fast merry go round

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    )
     
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  7. exchemist Valued Senior Member

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    Er, are you sure? I thought that at first, but on thinking further about it realised the centre is the one point that does NOT move. So, wherever on the circle the blue man fires, the bullet will travel in a straight line towards the centre and will reach it - which is what is shown.

    So [puts on crash helmet] I think it is correct.
     
  8. Pete It's not rocket surgery Moderator

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    The sideways motion of the gun imparts a sideways motion to the bullet.
     
  9. exchemist Valued Senior Member

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    Ah yes, so it does, quite right.
     
  10. Motor Daddy ☼☼☼☼☼☼☼☼☼☼☼ Valued Senior Member

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  11. Pete It's not rocket surgery Moderator

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    The bullet still goes in a straight line. Just not in same direction the rifle is aiming.
     
  12. eram Sciengineer Valued Senior Member

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    When viewing this, are we in a "rest" frame?



    If you weld a camera on to the merry-go-round, you will see the blue balls trace parabolic arcs to hit Mr. Red.
     
  13. eram Sciengineer Valued Senior Member

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  14. Lakon Valued Senior Member

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    Blue bullet hits Mr Red IMO.
     
  15. Pete It's not rocket surgery Moderator

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  16. eram Sciengineer Valued Senior Member

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  17. RJBeery Natural Philosopher Valued Senior Member

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  18. Lakon Valued Senior Member

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    However, the ball being rolled along the floor in the above clip, would be subject to friction and some counter rotation force. This is different to the OP scenario.
     
  19. RJBeery Natural Philosopher Valued Senior Member

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    At the end of the clip the girl throws the ball rather than rolling it, to the same effect. Also, check out the video I linked to above yours. The bullet would not fly through the center of the merry-go-round due to the perpendicular velocity component.

    Take the blue man off of the merry-go-round and put him on a train whizzing past the playground. He shoots just as he has red in his sights...do we expect red to be hit by that bullet?
     
  20. exchemist Valued Senior Member

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    Indeed not. In fact, it seems as if the blue man has completed about a quarter rotation by the time his bullet is shown as reaching the centre. In which case, given that it travels one radius r in that time, the blue man has travelled πr/2. So the tangential component of the bullet's motion is a bit more than 1.5 x its radial component: on this basis the trajectory of each blue bullet should be at an angle of about 57 degrees to the radius, at the instant they leave the gun. I think. But I was wrong earlier about all this.....
     
  21. RJBeery Natural Philosopher Valued Senior Member

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    No, that sounds right at first blush. It's possible that blue would actually shoot himself!

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  22. exchemist Valued Senior Member

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    Excellent! Although this can only happen in the case where the shooter moves at a speed comparable with that of the bullet. So in practice, either the bullet will drop feebly at his feet or, if the motion is fast enough for it to do damage, he will have already been reduced to a mush, or been torn apart, by the centripetal acceleration of the merry-go-round!
     
  23. RJBeery Natural Philosopher Valued Senior Member

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    Agreed. One thing is for sure...the OP graphic is rubbish.
     

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