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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?

Links related to my question:

Momentum a good definition

Sebastiano
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  • Both are caused due to the loss of kinetic energy. The dissipated energy was used to deform the body and change its shape. – Sam Feb 09 '20 at 16:36
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    momentum gives us the effect that we observe when the sphere impacts on a surface This is a vague statement that can’t be said to be true or false. – G. Smith Feb 09 '20 at 17:37
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    @G.Smith Sir I think OP wants to know if he can affirm that. I find it my duty to inform that OP is using a computer translator to convert his writing from Italian to English. –  Feb 09 '20 at 17:54
  • Yes, I am aware of the language issues. Sebastiano and I have been communicating for the past year. Vague statements are unaffirmable. – G. Smith Feb 09 '20 at 18:00
  • @G.Smith I hope that we can comunicate also in the present :-). You're right that "Vague statements are unaffirmable" but you try to understand me. I cannot be rigorous with my students and I have to find a strategy to make them understand the concept: they don't often remember even the simplest formulas and I dedicate my time with all my heart to my passion which is teaching. – Sebastiano Feb 09 '20 at 20:24
  • When my high-school physics teacher explained the importance of momentum, he focused on the conservation of momentum for closed systems. You should emphasize that there are not many conserved quantities, so each one is important, and that they can help you understand how a system behaves without understanding all of the details of how it evolves. Don’t focus on cars driving into walls. Focus on something like two billiard balls and how you don’t have to think about forces and accelerations to know something about the final state. – G. Smith Feb 09 '20 at 20:36
  • @G.Smith Hi :-) have you a bit of the time in chat? I'm here: https://chat.stackexchange.com/rooms/100303/general-chat – Sebastiano Feb 09 '20 at 20:53

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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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  • Meanwhile, a billion for your answer. The problem is that I have to explain the two concepts in separate moments to my students who do not know the details that you have correctly quoted. I wanted something more immediate for the two concepts. I will answer you later for any comments as I am about to go to church. Greetings. – Sebastiano Feb 09 '20 at 17:07
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    @Sebastiano For the benefit of your students I have added a comment about conservation of momentum in the collision. It's a question that often comes up. Enjoy the service! – Bob D Feb 09 '20 at 17:14
  • I am in complete panic with my students and you can't imagine. They want simple things all the time. I'm skipping a few topics and selecting the simplest ones. They're digital natives but they haven't experienced the reality... – Sebastiano Feb 09 '20 at 20:28
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    @Sebastiano Good luck and I know how you feel. I was tutoring a person not too long ago on the FE (Fundamentals of Engineering) test for his PE license. The very first thing he did when solving a problem was to take out his calculator. I had to keep telling him to put the damn thing away on focus on understanding the concepts. The last thing to do is use the calculator. – Bob D Feb 09 '20 at 21:11