Can someone confirm that a rolling coin that is falling will, at any instant, only have horizontal velocity directions that are parallel (those velocities being horizontal component velocities)?
It is counterintuitive because the coin will continually turn and travel a curved path, thus we would think that there is a vertical axis rotation with velocities of different directions tangent to a circle of an instant turn center. But I only see one direction horizontal component velocities of every part of the coin at any instant.
In Fig 1, a wheel rolls and the horizontal component velocities of every part of the wheel are oriented in one direction (top view) on the horizontal surface on which the wheel rolls except for the stationary part(s) at the contact point. Velocity arrows only indicate direction and not magnitude. Every non-zero horizontal component velocity is going to the right which is parallel to the wheel plane that defines the wheel’s rolling direction. If the wheel was stationary and falling sideways, the same thing (same direction horizontal component velocities) occurs except now orthogonal to the wheel plane. If we combine the rolling and falling motion we get what we’ll call tumbling of the wheel. The tumbling wheel also has same direction horizontal component velocities at any instant. Figs 2 and 3 show this tumbling wheel as it travels along a straight path. A better illustration of true rolling and falling motion of a wheel is shown in Fig 4. The wheel rolls and falls thus the velocity direction of the wheel center of mass is always at an angle to the wheel plane. Again, all directions of the non-zero horizontal component velocities on the rolling surface plane are parallel, at any instant. In Fig 5, a cornering vehicle wheel has horizontal component velocities of different directions on the horizontal rolling surface plane. The velocity directions are always tangent to an instant turn center circle. A vehicle wheel changes direction by a different mechanical reason compared to the rolling falling wheel.