3. Angular Momentum Theorem of Particles
4. The law of conservation of momentum of the particle
According to the angular momentum theorem of the particle, vector M=0, then d vector L/dt=0.
Vector L2=vector L1, or vector L=constant vector.
Concentrated force : The force experienced by an object points to or departs from a certain fixed point. This force is called concentric force.
在有心力的作用下
质点运动时
角动量守恒
（如行星绕太阳运动，对太阳角动量守恒）
The law of conservation of angular momentum of the particle : Particle suffered when combined force of a fixed reference point torque is zero , the point angle of the particle momentum remains unchanged.
The condition of the law of conservation of angular momentum of the particle : vector M=0.
The law of conservation of momentum and the law of conservation of angular momentum are different.
Angular momentum to the center of the circle (in a uniform circular motion)
[m1v1r1=m2v2r2]
The Angular Momentum Theorem and Conservation of Angular Momentum of the Particle System
1. The angular momentum theorem of the particle system
The mass point is the time rate of change of the angular momentum of a certain point, which is equal to the sum of the moments of all external forces acting on the system at that point.
2. The law of conservation of angular momentum of the particle system
When vector M outside=0, vector L=constant vector.
When the external moment of the particle system relative to a fixed point is zero, the angular momentum of the particle system remains unchanged at that point.
Newton's second law
The instantaneous force relationship, vector F = m vector a.
Space accumulation of force : work, kinetic energy, kinetic energy theorem.
1. Work
1. Constant force
F is constant force and the object moves in a straight line;
2. Variable force work
The mass point moves from point a to point b along the curve under the action of variable force;
The work done by each force on the mass point = the work of the combined force.
3. Power
Scalar P
2. Particle kinetic energy theorem
成立的参考系——惯性系
3. Kinetic energy theorem of particle system
Mass point system: external force + internal force
1. A system composed of two particles
Outside
A: Inside A:
A outside+A inside=Eka-Ekb=Dalter Ek.
The sum of internal forces must be zero, and the sum of work done by internal forces is not necessarily zero.
Not finished...
Prepared on 2021/3/26.