# Tag Info

### Speed at which the Moon moves past a point on Earth's surface?

The ground speed of the Moon can be thought of as the velocity of the bright spot on the surface of the Earth, projected from the Moon by a laser, pointing at the centre of the Earth, or as the lower ...
• 3,297

### Can the same rough surface provide frictional force on opposite directions for translation and rotation of a sphere under a tangential external force?

I don't think that your explanation is correct look at the FBD . you can move the force F to the center of mass ,thus you obtain torque $~F\,r~$. The force F cause the sphere to move to the right , ...
• 11.9k

### Can the same rough surface provide frictional force on opposite directions for translation and rotation of a sphere under a tangential external force?

YES, that explanation is correct. The direction of friction during rolling down a wedge is a very common misconception. However, it is very simple if we concentrate of the concept of friction. ...
• 21

### Angular velocity relative to some frame

Consider the case where A is itself a rotating frame. In such case, the angular velocity with respect to frame A will be more than just the angular velocity of B in an inertial frame, it must also ...
• 48.5k
1 vote

### Understanding the meaning of the directions of $\vec\omega$ and $\vec{L}$

There is direction vector (magnitude and direction) isn't fully meaningful, since the direction is ambiguous. We use: $$\omega_i = \epsilon_{ijk}r_jv_k$$ which rotates like a vector and defines a ...
• 33.6k
1 vote
Accepted

### Understanding the meaning of the directions of $\vec\omega$ and $\vec{L}$

It sounds like you got if figured out. The direction of $\vec \omega$ is always perpendicular to the plane defined by $\vec r\times \vec v$. Further, $\vec \omega$ is always parallel to the axis of ...
• 4,053
1 vote
Accepted

### Understanding angular velocity $\omega$ as a vector

Your reasoning is correct. The angular velocity has to be normal to the plane of rotation. If it, or any component of it, lay in the plane of rotation, that vector quantity would have to be changing ...
• 674

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