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I am in high school and my textbook says that

"a body is said to be in pure rotation if every point on that body moves in a circular path about a fixed axis of rotation"

but my doubt is that at any moment, I can define a linear velocity as $V=R\omega$ for any particle of that body, where $R$ is the distance of the particle from the axis of rotation.

but as velocity is defined in straight line motion then how can we say that the object is rotating?

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Notice, $V=R\omega$ is the linear or tangential velocity of any particle of a body rotating at angular speed $\omega$ at a particular instant of time $t$ because the tangential velocity $V=R\omega$ keeps on changing in direction from instant to instant while the magnitude $R\omega$ is constant if angular velocity $\omega$ of rotating body is constant.

Therefore, every point of a rotating body has a linear or tangential velocity at a every instant of time. A body moving at a velocity $V$ along a straight line can also be assumed to be moving on circle of ideally infinite radius.

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