# Thread: "Force due to circular motion"

1. Which one of the circle will act greater force on the object when the object is embedded between two rotating concentric circle?PHYSICS-"circular motion". Your answer is necessary to me! I think circle of smaller radius will act greater force on the object in radially outward direction that is centrifugal force. Since two opposite force is acting on the object. One is centrifugal force=mv^2/r and other is centripetal force=mv^2/R.Clearly,(centrifugal force)mv^2/r> mv^2/R(centripetal force) [ R>r]Hence, the force on object due to smaller circle is greater. Is it right or wrong? Please correct me with explanation!

2.

3. Allas, i hope this diagrammatic hint will provide you insight in solving your homework to which we naturally will never just give you the answer:http://imgs.xkcd.com/comics/centrifugal_force.png

4. Still I need clearification!!

5. You should probably forget the idea of a centrifugal force. Centrifugal force is a fictitious force in a rotating frame of reference, whereas you can discuss centripetal force in an inertial frame of reference.

As to the force on an object which is trapped between two rotating rings, there isn't a simple answer. The formula you used applies for a mass which is hypothetically concentrated at a single point. The mass of your object is distributed over a volume between two radii. To find the net force you could integrate over the entire volume.

6. Originally Posted by Harold14370
You should probably forget the idea of a centrifugal force. Centrifugal force is a fictitious force in a rotating frame of reference, whereas you can discuss centripetal force in an inertial frame of reference.
Actually, centriputal force and centrifugal force is the same. Though Wikipedia makes it appear to be the same. The derivations of both, from analytical mechanics is the same.

7. You mean there is something net force acting on object.And the net force is not 0.Is it?

8. Originally Posted by sagarkaran
You mean there is something net force acting on object.And the net force is not 0.Is it?
Looking at it from an inertial frame of reference, what you would say is that there is a centripetal force which causes a continuous acceleration. The acceleration is in the direction of the center of the circle. This acceleration is what makes the object follow a circular path when inertia makes it want to go off on a tangent.

The centripetal force is provided by the outer ring which is preventing it from flying off on a tangent. There isn't any force on the inner ring.

9. You have said that there isn't any force on the inner ring.But since inner ring is continuosly rotating it apply centrifugal force on the object.Is it right?

10. Originally Posted by sagarkaran
You have said that there isn't any force on the inner ring.But since inner ring is continuosly rotating it apply centrifugal force on the object.Is it right?
Take something heavy and tie a string to it. Spin it around in a circle. The centrifugal force pulls the string taut. There is no external force pushing the weight outward. You cannot push on something with a string. The "centrifugal force" just comes from the fact that there is a mass going around in a circle.

I tried to get you to think in terms of a centripetal force accelerating the mass in toward the center, but that didn't work. If you insist on talking about a centrifugal force, you will just have to accept that the force comes from the mass spinning in a circle.

11. Originally Posted by sagarkaran
You mean there is something net force acting on object.And the net force is not 0.Is it?
That is correct. Remember Newton's laws of motion?

First law: If an object experiences no net force, then its velocity is constant.
Second law: The acceleration a of a body is directly proportional to the net force F acting on the body.

In this case, the velocity is not constant; the object is under continuous acceleration. Therefore there must be a net force.

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