Tiêu đề ROTATIONAL MOTION.pdf ✅

CLASS IX PHYSICS INTRODUCTION: Rigid body: If there is no relative motion between any two particles of the body along the line joining them by the application of external force, then that body is called rigid body. Rotation of a rigid body about a given fixed line TRANSLATIONAL MOTION: All particles of the body move in parallel paths such that displacement of all the particles are same as that of the body then its motion is said to be translational. Example: For a rectangular block sliding down on an inclined plane without any sidewise movement, its mo- tion down the plane is such that all the particles of the body are moving together with same velocity. The rigid body is in pure translational motion. ROTATIONAL MOTION: A body is said to be in pure rotation if every particle of the body moves in a circle with same angular velocity and the centres of all the particles lie on a straight line called the axis of rotation. For the rotation of the rigid body about a fixed axis, every particle of the body moves in a circle, which lies in the plane perpendicular to the axis of rotation and has its centre on the axis of a rotation. Example: Consider the ceiling fan in your room. When it is on, each point on its body goes in a circle. Locate the centres of the circles traced by different particles on the three blades of the fan and the body covering the motor. All these centres lie on a vertical line through the centre of the body. The fan rotates about this vertical line. Axis of rotation of a ceiling fan Such a displacement of a rigid body in which a given line is held fixed, is called rotation of the rigid body about the given line. The line itself is called the axis of rotation. ROLLING MOTION: The combination of rotational and translational motion with regard to certain con- straints is called rolling motion. Example: The rolling motion of a cylinder down an inclined plane is a combination of rotation and translation. ANGULAR VARIABLES: ANGULAR DISPLACEMENT (θ) : It is the angle through which the radius vector representing the position of a particle that moves along a circle. ROTATIONAL MECHANICS SYNOPSIS - 1