A rigid body is an object that maintains its shape and volume during motion.
A rigid body can be considered as being made of many small parts marked by points.
Classification of motion based on the movement of individual points of a rigid body:
Parts of a rigid body move along circular paths, and all those circles lie in planes that are mutually parallel.
The axis of rotation – a straight line that passes through the centers of all circles (can go through the body or outside of it).
Angular velocity is the physical quantity that describes the speed of rotation of a rigid body.
When a body rotates, its points do not have the same linear velocities – points closer to the axis move slower, while points farther from the axis move faster. However, all points sweep the same angle in the same time, meaning they all have the same angular velocity. That is why angular velocity is used instead of linear velocity.
Points 1 and 2 are located at different distances from the axis of rotation. In the same time, they travel different distances and have different displacements.
The radius vectors of points 1 and 2 sweep the same angle in the same time. The angle swept describes the rotational motion. Based on that, angular displacement is defined. Angular displacement is a vector quantity.
The direction of normal acceleration matches the radius of the circular path, and the vector always points toward the center of the circle. That’s why it’s called radial or centripetal acceleration.
