o
Rotational analogue of Newton ’ s second law for the translational motion of a single particle : dl / st = τ
Torque and angular momentum of system of particles : o
The total angular momentum of a system of particles about a given point is addition of the angular momenta of individual particles added vectorially . o
Similarly for total torque on a system of particles is addition of the torque on an individual particle added vectorially .
o o
The torque resulting from internal forces is zero , due to o Newton ’ s third law i . e . these forces are equal and opposite . o o
These forces act on the line joining any two particles
The time rate of the total angular momentum of a system of particles about a point is equal to the sum of the external torques acting on the
system taken about the same point .
Conservation of Angular Momentum o
o
if the total external torque on a system of particles is zero , then the total angular momentum of the system is conserved
If text = 0 , then dL / dt = 0 => L = constant