Kinetics of Rigid Bodies: Impulse and Momentum

Kinetics of Rigid Bodies: Impulse and Momentum

This method relates the forces and moments acting over time to the change in linear and angular momentum of the body.

Angular Momentum (HH)

  • About Center of Mass (GG): HG=IGωH_G = I_G \omega
  • About Fixed Point (OO): HO=IOωH_O = I_O \omega

Principle of Impulse and Momentum

The system of momenta at time t1t_1 plus the system of impulses from t1t_1 to t2t_2 equals the system of momenta at t2t_2.

Linear Impulse-Momentum: m(vG)1+Fdt=m(vG)2m(v_G)_1 + \sum \int F \, dt = m(v_G)_2

Angular Impulse-Momentum (about GG): IGω1+MGdt=IGω2I_G \omega_1 + \sum \int M_G \, dt = I_G \omega_2

Conservation of Angular Momentum

If the sum of external angular impulses is zero, the angular momentum is conserved. (HO)1=(HO)2(H_O)_1 = (H_O)_2 This is useful for problems involving central forces or impacts where moments are zero about a specific point.

Example: Spinning Disk

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