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The mud flies off the tyre of a moving motor cycle in the direction:

  1. Jun 2, 2009 #1
    the mud flies off the tyre of a moving motor cycle in the direction:


    1)towards the center of the wheel
    2)towards the circular motion of the wheel
    3)along the tangent to the wheel
    4)away from the radius of the wheel.
  2. jcsd
  3. Jun 2, 2009 #2


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    Hint: Newton's second law (and what you know about circular motion / centripetal forces and velocities)
  4. Jun 2, 2009 #3


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    Very complex question this one.

    The forces are the following : Centrifugal, Adhesion of the mud and air friction. And the geometry of the wheel imposes a few sections.

    The one where the wheel touches the ground and begins to lift of it. Some mud is just vertically accelerated but is not fully bound by the tire so it only rises a bit vertically and slightly forwards. It's the mud that hits the engine hull of the bike, as it moves forward ( the bike hits the mud from a standing point of view).

    Next it's the mud that is actually taken with the tire so it is radially( from wheel p.o.v.) accelerated till the adhesion force cannot hold it to the tire. The breaking of the adhesion bond imparts some motion so this mud will fly at a small angle to the tangential.

    Of course there is the mud that actually sticks to the tire while it reaches the top. There air friction helps in breaking the adhesion as the top of the wheel moves with twice the speed of the bike. This mud will fly chaotic but will always be somewhere between the tangential and the vertical.

    True values for the angles are pointless as mud has many variables like humidity, density, viscosity etc. If water then there is actually a bit of flow going on so that will be even more complicated.
  5. Jun 2, 2009 #4


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    Welcome to PF!

    Hi shahzadzai! Welcome to PF! :smile:

    Mud will only stay on the wheel if there is a force keeping it there.

    So mud leaves the wheel when there is no force on it!

    Hint: what happens to something when there is no force on it? :wink:
  6. Jun 2, 2009 #5
    Tiny-tim..clever observation!!!!
  7. Jun 2, 2009 #6


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    Hi Naty1! :smile:

    :wink: I got the idea from Newton! :wink:
  8. Jun 2, 2009 #7


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    I'm not sure about mud, but in the case of water, a Coanda like effect will cause the water to mostly travel along the sidewalls towards the center of the tire before being ejected. It takes long enough that when riding a 10 speed, with no fender, you will get a wet stripe on your back from water that wasn't ejected until it had been "carried" along by the tire.

    My best guess is that mud and/or water get ejected in all directions depending on the tire, speed, slippage, and viscosity. That's why they invented fenders.
  9. Jun 2, 2009 #8
    :confused: Is that what you meant to type?
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