0
$\begingroup$

Suppose a circular object is rolling along a straight line. I seem to have seem vaguely that tangential velocity of the point of contact is equal to the velocity of center of mass(or that sort of things i am not really sure).What does the velocity of point of contact has anything to do with center of mass? I see that this is a concept which i haven't been taught in my school books. I would like to learn more about this concept. So could the physics lovers kindly explain this concept intuitively or provide some sources where i could learn them?It would be a great help to me.

$\endgroup$

3 Answers 3

0
$\begingroup$

If the circle is really rolling, you have no velocity at the point of contact. And this has nothing to do with the center of mass. the top point of the circle moves wth twice the velocity of the center.Just take any round thing like a round plate and tea it out. Many things are easier to understand by doing an experiment!

$\endgroup$
2
  • $\begingroup$ Thanks for the reply but could you please explain why there is no velocity at the point of contact theoretically?And as for the COM thing,here is a link which relates with COM but i didn't understand the post fully physics.stackexchange.com/questions/64555/… $\endgroup$
    – madness
    Sep 12, 2021 at 16:48
  • $\begingroup$ If you had a velocity at the point of contact, the thing would not roll but slip. so the velocity of the contact point is the slip velocity, thats why wrote " if it is really rolling" Why did you not try it out. ? $\endgroup$
    – trula
    Sep 13, 2021 at 10:20
0
$\begingroup$

If your round object is rolling (and not sliding) then the velocity (relative to the surface) at the point of contact is zero. The velocity of the object (relative to the surface) is defined by the motion of the center of mass. The speed of the point of contact (relative to the center) is the same as the speed of the center (relative to the surface), but in the opposite direction. The speed of the top of the object (relative to the center) is the same as at the bottom (but in the forward direction).

$\endgroup$
0
$\begingroup$
  1. For an observer in the frame of the ground, the velocity of the point of contact with the ground is zero if there is no slip. It is easier to understand if we move to the roll's axis frame. In this case the ground is being "moved" by the roll, and of course with the tangential speed of the roll. If velocities are the same in this frame, it must be the same for the ground's frame. As the velocity of the ground is zero for someone there at rest, the velocity of the point of contact must be also zero.

  2. If in the roll's axis frame, the velocity of a point at the periphery is $v$, that is the same "velocity" of the ground, then in the frame of the ground, the velocity of the roll's axis must be $-v$.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.