Definition Of Angular Momentum For A Particle
Where:
- = position from reference point
- = linear momentum
Units: kg - m2/s
Where:
Units: kg - m2/s
Vector cross product form.
L = Iω (rigid body about fixed axis):
Simplified angular momentum.
For extended rigid body rotating about fixed axis.
Total Angular Momentum: L_total = Sigma (r_i × p_i) or L_total = I_total ω:
Sum of angular momenta.
Discrete system:
Rigid body:
Simplified angular momentum.
For extended rigid body rotating about fixed axis.
Total Angular Momentum: L_total = Sigma (r_i × p_i) or L_total = I_total ω:
Sum of angular momenta.
Discrete system:
Rigid body:
Net External Torque: Sigmaτ_ext = 0 (or negligible):
Conservation condition.
When net external torque = 0, angular momentum conserved.
Applications:
Radius vector sweeps equal areas in equal times.
Direct consequence of angular momentum conservation (central forces exert no torque).
Work by torque through angular displacement.
Constant Torque: W = τ Deltaθ (if torque is constant):
Work-Energy Theorem for Rotation: W_net = DeltaK_rot = (1/2)Iω_f2 - (1/2)Iω_i2:
Net work equals change in rotational kinetic energy.
Relationship to Linear Power: Analogous to P = F - v in Linear Motion:
Rotational power analogous to translational.
Rotational power analogous to translational.
Constraint for pure rolling.
Total Kinetic Energy: K_total = (1/2)Mv_cm2 + (1/2)I_cm ω2:
Using rolling constraint:
Complete energy conservation.
Both can be conserved (different conditions).
Example: collision with rotation conserves both if no external forces/torques.
Where:
Units: kg - m2/s
Vector cross product form.
L = Iω (rigid body about fixed axis):
Simplified angular momentum.
For extended rigid body rotating about fixed axis.
Total Angular Momentum: L_total = Sigma (r_i × p_i) or L_total = I_total ω:
Sum of angular momenta.
Discrete system:
Rigid body:
Simplified angular momentum.
For extended rigid body rotating about fixed axis.
Total Angular Momentum: L_total = Sigma (r_i × p_i) or L_total = I_total ω:
Sum of angular momenta.
Discrete system:
Rigid body:
Net External Torque: Sigmaτ_ext = 0 (or negligible):
Conservation condition.
When net external torque = 0, angular momentum conserved.
Applications:
Radius vector sweeps equal areas in equal times.
Direct consequence of angular momentum conservation (central forces exert no torque).
Work by torque through angular displacement.
Constant Torque: W = τ Deltaθ (if torque is constant):
Work-Energy Theorem for Rotation: W_net = DeltaK_rot = (1/2)Iω_f2 - (1/2)Iω_i2:
Net work equals change in rotational kinetic energy.
Relationship to Linear Power: Analogous to P = F - v in Linear Motion:
Rotational power analogous to translational.
Rotational power analogous to translational.
Constraint for pure rolling.
Total Kinetic Energy: K_total = (1/2)Mv_cm2 + (1/2)I_cm ω2:
Using rolling constraint:
Complete energy conservation.
Both can be conserved (different conditions).
Example: collision with rotation conserves both if no external forces/torques.