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Why does a moving ball stop?

  1. Apr 2, 2015 #1
    Hello, members.

    Why does a moving ball stop and why does a bicycle stop when cyclist stops pedaling? What's the physics behind it? Kindly explain your answer.

    Thank you.
  2. jcsd
  3. Apr 2, 2015 #2
    Tho ball and the bike are both objects In motion if there is an opposing force such as friction, air resistance, or gravity they will slow the objects down to a stop that is why in a vacuum if an object is set into motion it will continue forever at the same speed until another force acts upon it
  4. Apr 2, 2015 #3
    Thank you Biscuit. When we stop pedaling, the bicycle does not stop immediately, it continues its motion for some time, then stops, why is it so? Could you explain it a bit?
  5. Apr 2, 2015 #4
    The forces even all together obviously are not as strong as a unmovable wall they are only constants pushing against the force that you initially started with the bike. So to restate that is you have constant forces vs a force that was started and then stopped so the constants can slowly push against it by colliding particles or friction between (gravity is a little more complicated but you get the idea). Sorry I might not be as helpful as you want I am only a sophomore who hasn't even finished ap physics yet
  6. Apr 2, 2015 #5
    Even if the ball is rolling on a perfectly level and frictionless surface it will still come to a stop due to the forces of deformation at the contact patch. The ball deforms as it contacts the surface and the normal force which would be perfectly vertical becomes angled against the direction of motion and brings the ball to a stop. Actually, even on a non-friction free surface, these deformation forces are higher than the friction forces.
  7. Apr 2, 2015 #6
    Are u saying objects slow down even in vacuum or are you just excluding a surface in my scenario because if it's the vacuum scenario that's very interesting
    Last edited: Apr 2, 2015
  8. Apr 2, 2015 #7
    Yes, even in a vacuum there will be deformation at the contact patch and the normal force will be slightly redirected away from the vertical and against the direction of rolling. If the object is extremely hard it will deform only slightly and will roll a long time, but there will be some deformation and eventually it will come to a stop.

  9. Apr 2, 2015 #8
    In simplest terms the answer is that while you are cycling you are converting chemical energy in your body into kinetic energy contained within the bike.,
    kinetic energy is the energy that something possesses due to its motion, it is now part of the system which is the bike.
    In a realistic situation that energy is gradually lost in a number of ways, for example some will be lost as heat in the less than perfect wheel hub bearings.
    the only way it would be lost instantly is if you hit a brick wall, in which case all of the kinetic energy is lost in the form of slightly heating up the bike and the wall.
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