SYSTEMS OF PARTICLES AND ROTATIONAL MOTION
Frequently Asked Questions
A system of particles is a collection of two or more particles considered together to study their combined motion.
Studying systems simplifies analysis by focusing on collective properties like centre of mass and total momentum.
A rigid body is an ideal body in which the distance between any two particles remains constant under applied forces.
It is motion in which all particles of the body move with the same velocity and acceleration at any instant.
Rotational motion is the motion of a body about a fixed axis where all particles move in circular paths.
It is an imaginary straight line about which a rigid body rotates.
The centre of mass is the point representing the average position of the mass of a system.
Yes, in some cases like a ring or a bent object, the centre of mass lies outside the material body.
Only external forces acting on the system govern the motion of the centre of mass.
The centre of mass remains at rest or moves with constant velocity.
It is the vector sum of the momenta of all particles in the system.
If the net external force on a system is zero, its total linear momentum remains constant.
It is the angle through which a body rotates about a fixed axis.
Angular velocity is the rate of change of angular displacement with time.
It is the rate of change of angular velocity with time.
Linear quantities depend on angular quantities and distance from the axis of rotation.
Torque is the turning effect of a force about a fixed axis.
Force magnitude, perpendicular distance from the axis, and direction of force.
It is a measure of a body's resistance to rotational motion about a given axis.
It depends on mass, shape, size, and distribution of mass relative to the axis.
Because mass distribution relative to the axis changes.
It is the kinetic energy possessed by a rotating body due to its rotation.
Rolling motion is a combination of translational and rotational motion.
The point of contact with the ground is momentarily at rest.
Angular momentum is the rotational analogue of linear momentum.
If no external torque acts, angular momentum of a system remains constant.
Folding arms reduces moment of inertia, increasing angular velocity to conserve angular momentum.
Torque is proportional to angular acceleration.
A pair of equal and opposite forces acting at different points producing rotation only.
Newton metre (N·m).
Kilogram metre squared (kg·m²).
In rotation, particles move in circles; in translation, all particles move parallel.
Rotation about a fixed axis without translation of the centre of mass.
Motion without any rotation, where orientation remains unchanged.
A wheel rolling on a road.
It simplifies analysis of motion of complex systems.
It explains machines, wheels, gears, sports motions, and planetary motion.
Conceptual, numerical, derivations, and application-based questions.
Linear momentum and angular momentum.
It simplifies rotational analysis by neglecting deformation.
It is the weighted average of position vectors of all particles based on their masses.
Internal forces cancel each other and do not affect the motion of the centre of mass.
It is the axis about which a body appears to rotate at a particular instant of time.
Yes, a body can rotate about a fixed axis without translational motion.
Yes, in pure translational motion, the body moves without any rotation.
Because the perpendicular distance of force from the axis is zero.
Mass farther from the axis increases moment of inertia and resists rotation more.
Angular velocity increases to conserve angular momentum.
Most machines involve rotating parts like gears, pulleys, and shafts.
Motion of centre of mass and conservation laws simplify complex rotational problems.
