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# CBSE Class 11th Physics Notes for ​ Chapter 7 System Of Particles And Rotational Motion

Chapter 7 System Of Particles And Rotational Motion

In a rotation of a rigid body about a fixed axis, every particle of the body moves in a circle, which lies in a plane perpendicular to the axis and has its centre on the axis.

CENTRE OF MASS
The centre of mass is taken to be a single point at which the entire mass of the system is concentrated and all the applied forces act at that point.

MOTION OF CENTRE OF MASS
The centre of mass of a system of particles moves as if all the mass of the system was concentrated at the centre of mass and all the external forces were applied at that point.

LINEAR MOMENTUM OF A SYSTEM OF PARTICLES
The total momentum of a system of particles is equal to the product of the total mass of the system and the velocity of its centre of mass.

COUPLE
A pair of equal and opposite forces with different lines of action is known as a couple.

CENTRE OF GRAVITY
The centre of gravity of an object is the point at which weight is evenly dispersed and all sides are in balance.