Is velocity a true physical quantity?
In physics, velocity is defined as the limit of a difference ratio. It's the differene between the position at two times divided by the time elapsed between the two positions. So there are always two positions needed, no matter how small the time duration gets. Now particles have no memory. They have a position and, so goes the argument, an instanteneous velocity. But a velocity is defined by two different positions. Positions are real. But velocities?
Comments (21)
Quoting Philofile
That's average velocity. The instantaneous velocity is the slope of the tangent of the position-time graph at that particular instant of time, dx/dt.
But that will not convince some folk because they didn't do enough maths at school.
A differential is a difference too.
Time = Measurement of time
Velocity = Measurement of motion
If there is no motion, even over an infinite period of time there is no change in position.
Velocity is measurement of two positions. The positions of particles change. But that goes hand in hand with two different times. But which of the two is fundamental?
How does the position of a particle change?
I could have given that answer myself. Every velocity is an average one.
It depends on the force acting on it.
So what's difference between speed and velocity? If I run around in a circle at 10m/sec what's my speed, average velocity, and my instantaneous velocity at t[sub]0[/sub]?
Speed is magnitude. Velocity is magnitude and direction. Scalar and vector.
By moving. But at no point you had a velocity. That's defined by us. Compare it with physics without time...
But time is consumed in the journey. My watch and my calender says so.
Also, explain this: a person X and Y are racing each other in a 100 m dash. X wins the race i.e. X and Y can be ordered in a sequence, X first, Y second. This ordering is not spatial, both ran 100 m. In what sense can you say that X is first and Y second? Time! Velocity then is a true physical quantity.
That's exactly what my question is about. Can you remember that jewish guy in English parlament smashing his wristwatch?
Your efforts are wasted on Banno. Some people think they know everything and refuse to learn anything.
To address your op, there is no such thing as a "physical quantity". "Physical" means of the body, where a body is a thing, or object. A quantity may be of one, or a multitude of objects. That's why quantity is an abstraction, or universal, and not something physical
Indeed, on this we agree, but it seems we disagree as to who...
Your inevitable presence here doubtless assures that this thread will have a long and unproductive continuation.
Can't a body, or matter, have quantities? Mass, charge, position, maybe velocity?
Perhaps he was onto something.
[quote=Dion Boucicault]Men talk of killing time, while time quietly kills them.[/quote]
:grin:
Jokes aside, timelessness is not something I have the wherewithal to tackle at the moment. I tried turning it over in my mind and I must admit I can't even parse the claim that time is an illusion. What does that even mean?
That we invented it. It's no illusion. It's very real. But Einsteins spacetime grant Nature to much.
These are all things we assign to the body, in predication. We might say that the body has something real, a property which corresponds to the concept assigned, but that all depends on the accuracy of the concept, in its capacity for modeling reality. That's why Banno's "instantaneous velocity" is a bad conception, when judged for truthfulness. Though it is a very useful concept, it's obvious that there is nothing real which corresponds with it.
"Mass" is similar, in the sense of being very useful, but not very truthful. It's like a magical power which we assign to a coherent group of particles which we observe to exist as a unified body. In theory, the massive object consists of a group of parts. But the theoretical parts, in summation, of each one's "mass" cannot account for the quantity of power that the unified whole is observed to have as "mass". So to be truthful we should represent this power which is attributed to "mass", as something which is produced by magic, or magically comes into existence, when parts are unified as a whole.
In a Timeless Universe, how are colors and tones defined?