Laws of conservation of momentum?

[Benjamin_harsh]

Problem Statement: Are this 3 topics comes under laws of conservation of momentum?
Relevant Equations: Are this 3 topics comes under laws of conservation of momentum?

Are this 3 topics comes under laws of conservation of momentum: energy lost due to impact, inelastic impact, purely elastic impact?

[Moderator's note: Moved from a homework forum.]

 

[BvU]

Yes. Momentum is conserved, so as long as there are no external forces involved, that is true for all three.

 

[Wrichik Basu]

Are this 3 topics comes under laws of conservation of momentum: energy lost due to impact, inelastic impact, purely elastic impact?

Are you asking whether the law of momentum conservation is valid in these cases? If yes, then the answer is also yes. During collision, elastic or inelastic, momentum is always conserved. In inelastic case, energy is not conserved in the sense that some amount of the initial energy is lost in the form of heat or sound energy.

 

[Orodruin]

energy is not conserved

Kinetic energy is not conserved. Important distinction.

 

[sophiecentaur]

Kinetic energy is not conserved. Important distinction.

Any Potential energy stored due to the deformation of objects is not conserved either. (Hysteresis is at work)

 

[anorlunda]

Those answers are correct, but they can be confusing to students who are shaky on energy conservation. Would it be better to say that "On Earth, energy is always conserved, but in this scenario some kinetic energy and potential energy can be transformed to heat energy."?

The "on Earth" or "locally" qualifier is needed because energy is not necessarily conserved in the whole universe.

I just worry that a B level student may be sloppy and read, "Kinetic energy is not conserved" as "Energy is not conserved."

 

[Herman Trivilino]

I just worry that a B level student may be sloppy and read, "Kinetic energy is not conserved" as "Energy is not conserved."

The important distinction is between mechanical energy and thermal energy. Students should understand that "Mechanical energy is not conserved" except under the most ideal of conditions.