Physics of a Merry-go-round

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

  1. Boris2 Valued Senior Member

    Messages:
    1,106

    Please Register or Log in to view the hidden image!



    Is there anything wrong with the physics of this GIF?
     
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. Russ_Watters Not a Trump supporter... Valued Senior Member

    Messages:
    5,051
    Yeah, blue dude is aiming his gun at the guy in the center, so he shouldn't be hitting him.
     
  4. Google AdSense Guest Advertisement



    to hide all adverts.
  5. John Connellan Valued Senior Member

    Messages:
    3,636
    They are very slow moving bullets! (or an extremely fast merry go round

    Please Register or Log in to view the hidden image!

    )
     
  6. Google AdSense Guest Advertisement



    to hide all adverts.
  7. exchemist Valued Senior Member

    Messages:
    12,451
    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 Registered Senior Member

    Messages:
    10,167
    The sideways motion of the gun imparts a sideways motion to the bullet.
     
  9. exchemist Valued Senior Member

    Messages:
    12,451
    Ah yes, so it does, quite right.
     
  10. Motor Daddy Valued Senior Member

    Messages:
    5,425
  11. Pete It's not rocket surgery Registered Senior Member

    Messages:
    10,167
    The bullet still goes in a straight line. Just not in same direction the rifle is aiming.
     
  12. eram Sciengineer Valued Senior Member

    Messages:
    1,877
    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

    Messages:
    1,877
  14. Lakon Valued Senior Member

    Messages:
    1,117
    Blue bullet hits Mr Red IMO.
     
  15. Pete It's not rocket surgery Registered Senior Member

    Messages:
    10,167
  16. eram Sciengineer Valued Senior Member

    Messages:
    1,877
  17. RJBeery Natural Philosopher Valued Senior Member

    Messages:
    4,222
  18. Lakon Valued Senior Member

    Messages:
    1,117
    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

    Messages:
    4,222
    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

    Messages:
    12,451
    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

    Messages:
    4,222
    No, that sounds right at first blush. It's possible that blue would actually shoot himself!

    Please Register or Log in to view the hidden image!

     
  22. exchemist Valued Senior Member

    Messages:
    12,451
    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

    Messages:
    4,222
    Agreed. One thing is for sure...the OP graphic is rubbish.
     

Share This Page