What Lies Beneath the Definition of Velocity?

[arul_k]

Yes,I do know that the definition of velocity is rate of change of displacement, but I sometimes wonder if there is something more fundamental to velocity. Is there a funamental change in an object or the space around it that enables the object to cover a greater distance in a certain time interval. In other words does the appication of a force cause an intrinsic change that enables an object to displace itself a little further in a given instant. Any one out there thinking on similar lines...

 

[Dadface]

Yes,I do know that the definition of velocity is rate of change of displacement, but I sometimes wonder if there is something more fundamental to velocity. Is there a funamental change in an object or the space around it that enables the object to cover a greater distance in a certain time interval. In other words does the appication of a force cause an intrinsic change that enables an object to displace itself a little further in a given instant. Any one out there thinking on similar lines...

Are you familiar with Newton's second law?In a nutshell the greater the resultant force acting on an object and the smaller the mass of the object the more it will accelerate.
(F=Ma).

 

[McVador]

Ah, this is the question that always boggled my mind in high school. I thought of moving objects as having some sort of invisible container filled with kinetic energy, that grew as the object accelerated. Then, I read about Einstein's theory of relativity, and it struck me that no, there is no invisible container of energy. Here's why: that container would have to be different for each and every observer, because speed is relative! So kinetic energy is really just an illusion, moving objects do not actually "contain" kinetic energy, kinetic energy is just a way for physicists to more easily calculate things. It's the same with "potential" energy: objects do not actually contain "potential" energy, it's just a way for us humans to look at things.

Does that help?

 

[Drakkith]

On the risk of causing more confusion, I'll say this.

Don't confuse our definitions of energy as meaning that they contains "something". Energy is defined as the capacity to do work; the property of a system that diminishes when the system does work on any other system, by an amount equal to the work so done; potential energy.

When we say something "contains energy" we mean that it has the potential to change something else in the system in some way. I know most people have a misconception that energy is "something" that is as real as matter. It is not. Contray to what movies, shows, and most literature say, you cannot have a "Big ball of energy" or anything like that.

It's not that it is simply a way of calculating things, energy is a real property of all matter and mass.

 

[McVador]

Well first you say that energy doesn't exist except as "the potential to change", then you said "energy is a real property of all matter and mass".

I know that energy = mass * C^2, which basically proves the equivilence of mass and energy, but that is not his question. He wants to know specifically about kinetic energy, and I think me an you both agree that objects do not "contain" kinetic energy, but scientist and mathametitions sort of pretend that they do to make calculating things easier. Objects do have mass, however, and mass is made of energy, but that's a different topic.

...

hmm, I just thought of something though... when an object gets close to the speed of light, the energy put into speeding it up gets converted into mass in order to preserve the conservation of energy. So in that way, I guess objects DO acquire a sort of "intrinsic" energy! That only happens when an object approaches the speed of light however, and even then each observer sees it differerently: someone moving nearly the same speed, for example, wouldn't notice any change in mass, correct?

 

[Drakkith]

hmm, I just thought of something though... when an object gets close to the speed of light, the energy put into speeding it up gets converted into mass in order to preserve the conservation of energy. So in that way, I guess objects DO acquire a sort of "intrinsic" energy! That only happens when an object approaches the speed of light however, and even then each observer sees it differerently: someone moving nearly the same speed, for example, wouldn't notice any change in mass, correct?

You are correct. If I were traveling at very close to the speed of light, I would not be any more massive from my point of view.

And I realize my explanation is a little confusing. I'm not very good at explaining things lol. I just meant to say that energy is not what most people imagine it as. I wasn't disagreeing with you or anything.

 

[arul_k]

Hey, thanks for the replies, honestly, I was expecting to be laughed right out of Physics Forums for posting this question.

Regarding the question of velocity, If there were an intrinsic change in an object (and not just the kinetic energy) then velocity and mass would no longer be relative, Provided this change could be measured.

 

[Drakkith]

Hey, thanks for the replies, honestly, I was expecting to be laughed right out of Physics Forums for posting this question.

Regarding the question of velocity, If there were an intrinsic change in an object (and not just the kinetic energy) then velocity and mass would no longer be relative, Provided this change could be measured.

I'm not an expert, but that sounds pretty logical to me.