# Object Movement in space

1. Jun 23, 2013

Should an object for argument sake a cube be travelling in space at a stable rotation, if a small object travelling at a high velocity collided with the edge of the cube enough so that on earth if fastened the cube would spin. in space however would this object spin/rotate in a single position or move awkwardly in a almost random direction. If so would the actions of the collision work when the small object colliding with the cube remains the same size yet the cube is 100x its size.

Random debate between friends, however neither of us have the knowledge required to actively agree with certainty on any particular point. if it requires any more explanation please let me know.

2. Jun 23, 2013

### D H

Staff Emeritus
The object is a cube, so it presumably has a scalar inertia tensor. The behavior for such an object is rather uninteresting. If on the other hand the space ship was a book (three different principal moments of inertia) the behavior is quite complex. Now you can get into a situation where angular velocity and angular momentum point in different directions. The object will exhibit all kinds of weird behavior. Angular momentum will still be constant, but angular velocity is not. As Goldstein put it, "The polhode rolls without slipping on the herpolhode lying in the invariable plane."

3. Jun 23, 2013

### solar71

The object (large cube) in space if hit on its edge would not spin in any sort of uniform fashion.
Because its central axis is not tethered to any stationary object.
In 99.999% of instances the large cube would wobble about all over the place. But if you could hit the cube very very precisely you could get it to spin without wobbling, BUT it would drift ever so slightly.

4. Jun 23, 2013

### D H

Staff Emeritus
A cube will do just that. You need at least one of the principle moments of inertia to differ from the other two to get any kind of interesting motion. But even then it won't be that interesting. Things only get really interesting when all three principal moments of inertia are different from one another.

The wobbling results from the $(\mathbf I \vec{\omega})\times \vec{\omega}$ term in the torque-free equations of motion for a rigid body.