Relation between position vector and velocity vector

AI Thread Summary
The discussion clarifies that the velocity vector ##\vec{\dot{r}}## is not always parallel to the position vector ##\vec{r}}##, as a particle can move in any direction. It highlights that the equation in question pertains to the acceleration vector for a central force, which aligns with the position vector. The conversation emphasizes the distinction between the radial and angular components of motion, noting that the last equation refers specifically to the radial component of velocity. Additionally, there is a clarification that ##\vec{\dot{r}}## represents the velocity vector, while ##\vec{\ddot{r}}## denotes the acceleration vector. Overall, the key takeaway is understanding the relationship between velocity and acceleration in the context of central forces.
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The equation following (3.80) seems to suggest that the velocity vector ##\vec{\dot{r}}## must always be parallel to the position vector ##\vec{r}##. But clearly this is not true as a particle's velocity can be in any direction.

What's wrong?

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That looks like the acceleration vector for a central force, which must indeed be in the direction of the position vector (from the central point).

The last equation says "the component of the velocity in the radial direction". There is an angular component as well.
 
PeroK said:
That looks like the acceleration vector for a central force, which must indeed be in the direction of the position vector (from the central point).

The last equation says "the component of the velocity in the radial direction". There is an angular component as well.

##\vec{\dot{r}}##should be the velocity vector. The acceleration vector should be ##\vec{\ddot{r}}##.

I think I get it. ##\dot{r}\neq|\vec{\dot{r}}|##.
 
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