Energy Lost During Purely Inelastic Collisions

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Discussion Overview

The discussion revolves around the energy lost during purely inelastic collisions, focusing on the application of conservation of momentum and the relationship between kinetic energy loss and the deformation of colliding objects. Participants explore theoretical implications and interpretations of the collision mechanics in a one-dimensional context.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that the velocity of the combined object after a purely inelastic collision is determined by the initial speed of the moving object and the masses involved, which also influences the amount of kinetic energy lost.
  • Others argue that energy loss should be related to the extent of smashing and deformation during the collision, suggesting a connection between these physical processes and energy dissipation.
  • A later reply questions whether the energy required for deformation sets a critical condition for achieving an inelastic collision, depending on the relative masses and initial speed of the objects.
  • Some participants affirm that the energy lost to deformation is equal to the kinetic energy loss, while others suggest that the relationship may not be straightforward and could depend on material properties.
  • One participant provides a mathematical expression for energy loss in a perfectly inelastic collision, indicating a specific formula involving reduced mass and relative velocity.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between energy loss, deformation, and the conditions necessary for inelastic collisions. There is no consensus on whether the energy loss is solely determined by the collision mechanics or if other factors, such as material properties, play a significant role.

Contextual Notes

Participants mention the need for specific energy conditions related to material behavior, such as elastic and plastic regions in stress-strain curves, which may influence the nature of the collision. However, these aspects remain unresolved in the discussion.

jon4444
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I'm curious about how the math comes out when you apply conservation of momentum to the theoretical problem of a moving object having a purely inelastic collision with another stationary object in a single dimension. Since the velocity of the combined object is entirely determined by the initial speed of the moving object and the masses of the objects, these parameters also determine the amount of energy lost (when you compare the kinetic energy of the initial object versus that of the combined object).
But shouldn't energy loss be related to how much smashing and deformation goes on during the collision? Is there another interpretation I'm missing?
 
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jon4444 said:
I'm curious about how the math comes out when you apply conservation of momentum to the theoretical problem of a moving object having a purely inelastic collision with another stationary object in a single dimension. Since the velocity of the combined object is entirely determined by the initial speed of the moving object and the masses of the objects, these parameters also determine the amount of energy lost (when you compare the kinetic energy of the initial object versus that of the combined object).
But shouldn't energy loss be related to how much smashing and deformation goes on during the collision? Is there another interpretation I'm missing?
You have assumed that the two objects smash together and then continue to move together as one object. The energy lost to the smashing and deformation required to reach that state is exactly equal to the kinetic energy loss.
 
jon4444 said:
these parameters also determine the amount of energy lost (when you compare the kinetic energy of the initial object versus that of the combined object).
Yes.

jon4444 said:
shouldn't energy loss be related to how much smashing and deformation goes on during the collision?
Yes. The two amounts are the same.
 
But shouldn't energy loss be related to how much smashing and deformation goes on during the collision?
But shouldn't smashing and deformation be related to energy loss? Or even, determined by it.
 
so, say certain materials require a certain amount of energy to join together (the smashing and deformation)--this essential sets a critical condition for if you could have an inelastic condition (i.e., only under certain relative masses and initial speed).
Is that a correct interpretation of the situation?
 
jon4444 said:
so, say certain materials require a certain amount of energy to join together (the smashing and deformation)--this essential sets a critical condition for if you could have an inelastic condition (i.e., only under certain relative masses and initial speed).
Is that a correct interpretation of the situation?
Yes, for example, if a material has an elastic region and a plastic region in its stress strain curve then you would not get a plastic collision at low energies.
 
Since the OP asked about the maths, then (for the record) energy loss in a perfectly inelastic collision is given by:

## ΔE = ½μΔv^2 ##

where μ is the reduced mass of the colliding objects and Δv their relative velocity.
 
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