# Effect of forces inside a sphere

What would be the effect of applying two parallel forces of the same value at opposite points of the equator inside a sphere?

Common sense tells me that it wouldn't move, but it seems that it could cause a torque from the point of contact with the ground that may not be balanced with the rolling resistance. I mean, would it create movement if

$$2Fr \gt \delta mg$$

where $F$ is the force applied at one of the two points, $r$ and $m$ are the radius and the mass of the sphere, $g$ is the gravity force and $\delta$ is the rolling resistance coefficient.

Then imagine that the two forces are created by two internal motorized wheels (blue schema).

• Are the forces directed towards the center of the sphere or tanget to the surface? Apr 26, 2017 at 19:34
• Tangent to the surface, sorry for not specifying Apr 26, 2017 at 20:10
• What exerts these forces? Do you have a small levitating rocket engine in there, then sure, it could roll. Do the forces come from something mounted onto the sphere, then it won't. Apr 26, 2017 at 20:48
• It would be good if you could add a sketch if the setup. As I read it, the two forces are pushing at two opposite points inside the sphere and then you mention rolling friction which is a very varying type of force. Would you mind sketching out your thinking? Apr 26, 2017 at 20:51
• @Steeven ok, just give me a moment... Apr 26, 2017 at 20:54