Is Velocity Always Constant in Physics?

[ObsessiveMathsFreak]

What the hell is going on here.

I read someone arguing that velocity was a constant and now there is talk of making t a dependant variable.

Can someone explain what points are trying to be made here?

 

[dr-dock]

actually the problem was:
whenever one defines V as dx/dt V has to be constant.
if V is variable then dx=Vdt+tdV instead of dx=Vdt.

what do you think of it as a mathematician, ObsessiveMathsFreak?

 

[Hurkyl]

And to me it seems that Dock is going through a phase I once went through... except that Dock is promoting his misunderstandings to the level of belief while I spent effort trying to figure out the underlying structures that rigorously support these types of manipulations.


I thought it might help dock to see the explicit pieces that go into some of these manipulations; I know it would've helped me back then.

Hurkyl

 

[Ben-CS]

Actually, dx = vdt does not imply that v is a constant, it merely implies that x = vt − ∫tdv. I have no problem with this.

 

[ObsessiveMathsFreak]

v = dx/dt

I think this fact is agreed upon by all at least.

What does it mean. It means that velocity is the instantaneous rate of change of distance. In other words, at any given instant, v is a measure of how fast you are going.


but what happens in the case of

x = Sin(t)

does your formula work then.