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Can I affirm that the momentum gives us the effect that we observe when the sphere impacts on a surface (for example if a car impacts against a wall we observe fractures and visual damage)?

After, for the kinetic energy can I affirm that is the energy released or dissipated when a car impacts against a wall?

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Momentum a good definition

Sebastiano
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1 Answers1

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After, for the kinetic energy can I affirm that is the energy released or dissipated when a car impacts against a wall?

Yes you can, but it should be qualified that it is the macroscopic kinetic energy of the car that is dissipated in the collision. The macroscopic kinetic energy is the kinetic energy associated with the velocity of the center of mass of the car as a whole.

In the collision the loss of macroscopic, or external, kinetic energy becomes an increase in the microscopic internal energy (kinetic plus potential) associated with the fracturing and visible damage to the car (and possibly the wall as well) resulting in raising the temperatures of the colliding objects. Overall, external plus internal energy is conserved. Only the macroscopic kinetic energy is not conserved.

I would add that the difference between momentum and macroscopic kinetic energy in your collision example is that momentum is conserved whereas macroscopic kinetic energy energy would not be. Macroscopic kinetic energy is only conserved in a perfectly elastic collision. Perfectly elastic collisions do not exist at the macroscopic level.

As a final comment, it is not uncommon for one to think momentum is not conserved when a wall brings a car to a stop since the wall does not appear to move. But the wall/earth actually does move to conserve momentum. Thing is its mass is so huge compared to the car, its movement is so infinitesimal as to be immeasurable and is therefore ignored from a practical perspective.

Hope this helps.

Bob D
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