Physics · Class 11 · Chapter 6
System of Particles and Rotational Motion
13 lessons 105 min 2 simulations
Real bodies have size, and they turn as well as move. This chapter treats an extended body as a system of particles: it locates the centre of mass and shows that it moves as if all the mass and all the external force were there, then builds rotation about a fixed axis step by step, from angular velocity and the vector product to torque, angular momentum, equilibrium, moment of inertia, the rotational equations of motion and the conservation of angular momentum.
What the exam asks
NEET asks for the centre of mass of a few point masses or a composite plate, the motion of the centre of mass after an explosion, torque as r × F and its magnitude rF sin θ, reactions from the principle of moments, moments of inertia from the standard table, τ = Iα with ω² = ω₀² + 2αθ, and Iω = constant for a spinning skater or child. Marks are lost by taking r instead of the perpendicular distance, using rpm without converting to rad/s, forgetting that I depends on the axis, and assuming kinetic energy is conserved when I changes.
Lessons
13 lessons · 105 min
1Rigid bodies and their motionNCERT §6.17 min2Centre of massNCERT §6.28 min3Motion of the centre of massNCERT §6.3, §6.47 min4Vector product of two vectorsNCERT §6.57 min5Angular velocity and angular accelerationNCERT §6.6, §6.6.17 min6Torque and angular momentumNCERT §6.77 min7Equilibrium of a rigid bodyNCERT §6.86 min8Principle of moments and centre of gravityNCERT §6.8.1, §6.8.211 min 1 sim9Moment of inertiaNCERT §6.97 min10Kinematics of rotationNCERT §6.106 min11Dynamics of rotationNCERT §6.116 min12Angular momentum and its conservationNCERT §6.12, §6.12.110 min 1 sim13Chapter reviewMust-know facts, traps and formulas16 min