You are here:

# Physics/Spinning sphere

supper wrote at 2008-02-22 16:13:50
an easy way to make it very large with few materials is to have your craft attached by a long tether to a large weight and you spin around the center of the tether.

Erik wrote at 2010-12-24 09:54:28
Hmm... random I found this question(searching for something totally different), but perhaps I can clear up a few points:

A spinning object does not "create gravity" at all. Instead it is the objects themselves placed inside the sphere that push out against the surface(because the sphere is stopping them from going where they want due to inertia(ie tangent to the sphere))

The force of the sphere causes them to be caught in the curved path instead of the straight path they want to go, and this causes them to "feel gravity".

Imagine a human-sized hamster wheel in space spinning at the correct speed to simulate earth gravity. You could be floating in a space suit in the middle of the wheel and not "feel" any gravity. You could, while floating, touch the side of the wheel and not feel gravity, just it rushing under your hand. It is only when you yourself are spinning(perhaps by touching the wheel hard enough that its friction causes you to start moving in a circle along with it) that you feel any force.

When looking at this problem in the correct light, it should be obvious that at the north/south pole of a spinning sphere, that a person standing there would not experience any acceleration(gravity) because they themselves would only be spinning, the sphere is not stopping them from escaping. If they jumped, they would float to the other side.

Multiverse wrote at 2012-12-28 10:15:56
If you put three skewers through an orange in any orientation, and try to rotate the orange around all of them, you will make orange juice.

As the original answer states, decomposition of motion into orthogonal components is not the same as actually moving along those components.

I think you may be confusing forces with motion.  You can exert force on a sphere in three different directions, and the resulting motion will be the combined effect of all those forces.  Imagine an orange with thrusters placed tangential to the surface in three orthogonal directions.  The orange would indeed spin, and it would do so about a single axis.

Physics

Volunteer

#### Expert

##### Expertise

I can help with understanding physics that does not involve eggs. I will NOT help with academic or professional questions, which are NOT limited only to homework. Please do not waste your time by asking a question that comes out of ANY kind of academic, professional, or business matters.

##### Experience

Have been fascinated by physical laws ever since I learned, at age seven, that magnets work under water. My study continued through college and has not ceased even after I retired.

Education/Credentials
B.A. in Physics (with honors) from University of California at Berkeley.M.A. in Physics (with honors) from University of Texas Austin.