Does the equation dr/dr = w(t)xr(t) hold true for a changing axis vector?

  • Thread starter Thread starter yetar
  • Start date Start date
  • Tags Tags
    Axis Motion
AI Thread Summary
The discussion centers on the equation dr/dt = w(t) x r(t) in the context of motion around a fixed axis, where r(t) is the position and w(t) is the angular velocity. The original question queries whether this equation holds true when the axis vector D is time-dependent. Participants clarify that dr/dt is the correct notation and explore the implications of a non-constant axis vector on the equation's validity. The consensus is that the relationship may change if D(t) varies with time, but further clarification is needed from others in the forum. The topic highlights the complexities of rotational motion when dealing with changing vectors.
yetar
Messages
53
Reaction score
0
In a motion about a fixed axis, where the position is r(t) and the angular velocity is w(t), we know that dr/dr = w(t)xr(t).
My question, does this equation remains true if the axis vector is changing by the time t? Why so?
Thank you.
 
Physics news on Phys.org
dr/dr = w(t)xr(t).
Do you mean dr/dt ? I'm not clear about the description.
 
Mentz114 said:
Do you mean dr/dt ? I'm not clear about the description.

Yes, dr/dt.
r(t) = r0*R+h0*D
Where r0 is a constant distance scalar, and h0 is the distance from the plane that D is normal to.
D is a unit vector, the axis of rotation, so the particle rotates around the axis D. And R is a unit vector, which is the radial vector. R is the opposite direction of the centerpital accelaration.
R is dependant of t, the time.
On a motion around a fixed axis, D is a constant vector, and in this case:
dr/dt = r0*dR/dt = wxr
My question is, what happens when D is not a constant, but instead D(t) is a vector dependant of the time t?
Is it still true that dr/dt = wxr?
Where w is the angular velocity.
 
Yetar, I'm sorry I can't answer your question. Maybe someone else can help.
 
Thread 'Collision of a bullet on a rod-string system: query'
In this question, I have a question. I am NOT trying to solve it, but it is just a conceptual question. Consider the point on the rod, which connects the string and the rod. My question: just before and after the collision, is ANGULAR momentum CONSERVED about this point? Lets call the point which connects the string and rod as P. Why am I asking this? : it is clear from the scenario that the point of concern, which connects the string and the rod, moves in a circular path due to the string...
Back
Top