Rod swinging and hitting a ball

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SUMMARY

The discussion centers on a physics problem involving a uniform rod and a ball, specifically analyzing the collision dynamics when the rod is released from a 45-degree angle. The rod has a mass of 1 kg and a length of 0.2 m, while the ball has a mass of 0.1 kg and a radius of 2.85 cm. Participants explore the conservation of angular momentum and energy, leading to calculations of angular velocities before and after the collision, as well as the ball's translational speed. Key equations include the moment of inertia of the rod and the coefficient of restitution, highlighting the complexities of elastic versus inelastic collisions.

PREREQUISITES
  • Understanding of angular momentum and its conservation principles
  • Familiarity with moment of inertia calculations, particularly for rods
  • Knowledge of the coefficient of restitution and its application in collision problems
  • Proficiency in energy conservation principles in mechanical systems
NEXT STEPS
  • Study the derivation of the moment of inertia for various shapes, focusing on rods and spheres
  • Learn about the coefficient of restitution and its implications in elastic and inelastic collisions
  • Investigate the effects of friction on rolling motion and its role in collision scenarios
  • Explore advanced topics in rotational dynamics, including angular impulse and torque
USEFUL FOR

Students and professionals in physics, particularly those focusing on mechanics, collision analysis, and rotational dynamics. This discussion is beneficial for anyone looking to deepen their understanding of collision problems involving rigid bodies.

  • #31
erfz said:
@haruspex
I'm thinking now, would it be possible to set your axis on the table that the ball sits on and treat the rod and ball as a single system?
This would eliminate frictional torque, I think.
Do you see anything wrong with that?
But then you would have torque from the unknown reaction at the rod's hinge.
You can take anywhere as your reference points for angular momentum, but if that means dragging in the reaction force from the hinge or the friction from the table then you will need to bring in a linear momentum equation as well in order to eliminate the unknown. The great benefit of using the rod's axis for its equation and the point of contact of the ball with the table for its equation is that we never get those impulses in the equations.
 
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  • #32
haruspex said:
But then you would have torque from the unknown reaction at the rod's hinge.
You can take anywhere as your reference points for angular momentum, but if that means dragging in the reaction force from the hinge or the friction from the table then you will need to bring in a linear momentum equation as well in order to eliminate the unknown. The great benefit of using the rod's axis for its equation and the point of contact of the ball with the table for its equation is that we never get those impulses in the equations.
Ah, shoot. I forgot about that completely. Thank you very much!
 

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