Confusion regarding centrifugal force

In this https://youtu.be/YCrFwQtW5o0 sir took a disk and demonstrated that the particles kept on it fly away due to centrifugal force.

Now, suppose I take a ring in free space and a placed particle in its interior (Not on circumference).

If we observe it from a frame of reference of the ring, since ring is rotating the particle must experience a centrifugal force and hence it will fly off.

But from space frame, it doesn't.

Why does this happen?

I am also attaching a picture of my demonstration.

In the picture there are two scenarios first is the same as shown in the video .

In the second picture will the particle experience a centrifugal force or is it n it is necessary that the particles must somehow interact with the rotating frame to experience a pseudo force.

• sorry, your question is not clear to me , Could you rephrase your scenario? Dec 3, 2020 at 11:33
• A particle inside a ring out in outer space is not in contact with the ring. So it won't move when the ring is spinning. A coordinate system attached to the spinning ring will thus move around this particle periodically - the particle will not move away or out of the ring. The particles in the video are only moving and thrown away from the disc due to friction. Dec 3, 2020 at 14:07
• So in order to apply pseudo force on a particle in rotating frame it is necessary that the particles must somehow interact with the rotating frame? Dec 3, 2020 at 14:27

If we observe it from a frame of reference of the ring , since ring is rotating the particle must experience a centrifugal force and hence it will fly off .

But from space frame, it doesn't.

Why does this happens ?

The centrifugal force is not the only inertial force in a rotating reference frame. You are neglecting the Coriolis force. The Coriolis force is given by $$-2 m (\vec \omega \times \vec v)$$ where $$\vec \omega$$ is the angular velocity of the rotating reference frame relative to the inertial frame and $$\vec v$$ is the velocity in the rotating frame.

Note that your particle has a velocity of $$\vec v = -\vec \omega \times \vec r$$. This is in the opposite direction as the centrifugal force and is twice the magnitude. So the total inertial force is centripetal and the particle undergoes uniform circular motion in the rotating frame, as expected.

It is not necessary for a particle to be in contact with anything to experience the inertial forces. They apply to all objects in the frame.

• Thanks everything makes sense now i mistook. Coriolis force Dec 3, 2020 at 16:42