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andyrk
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for a perfectly rigid body, how can one identify what is the axis of rotation of the rigid body? What is the condition required for an axis to be called the axis of rotation?
andyrk said:Yes so in case of rotation and translation of a sphere the centre of mass doesn't have zero velocity. Yet it is considered as axis of rotation.
Or is it that it is considered axis of rotation just when we are applying torque and not after it because then it has gained some velocity?
So that's why we take the bottom most point in the sphere rolling without slipping as the instantaneous axis of rotation?
So what would be the axis of rotation if a sphere is rolling with slipping?
voko said:This can be correct only in a reference frame co-moving with the sphere. In any other frame, the axis is elsewhere.
andyrk said:What would be the axis of rotation in an inertial frame of reference? Like ground?
Better: The axis of rotation is that locus where the instantaneous velocity as expressed in some reference frame is zero.voko said:For the record, the axis of rotation is defined as a locus where the velocity is zero.
You're looking at things from a frame of reference that differs from the frame in which the axis of rotation is arbitrarily defined in this particular example.andyrk said:Yes so in case of rotation and translation of a sphere the centre of mass doesn't have zero velocity. Yet it is considered as axis of rotation.
An axis of rotation for a rigid body is an imaginary line around which the body rotates. It is a fixed point that remains stationary while the body moves.
The axis of rotation for a rigid body can be identified by observing the direction and point of rotation. The axis will be perpendicular to the plane of motion and will pass through the center of mass of the body.
A fixed axis of rotation remains in the same position throughout the motion of the body, while a variable axis of rotation changes position as the body rotates. A fixed axis can be identified easily, while a variable axis requires more complex calculations.
A rigid body must have a symmetrical shape and a uniform mass distribution in order to have a fixed axis of rotation. Additionally, the force acting on the body must be parallel to the axis of rotation.
Yes, a rigid body can have multiple axes of rotation if the motion is complex and involves multiple forces acting on different points of the body. However, there will always be one primary axis of rotation that can be identified.