# Question About Position, Velocity, etc. Fields

Why in my textbook does it define a velocity field as V = V(x,y,z,t) where x, y, and z are functions of time.

I'm mixed up because if x, y, and z are functions of time, why does there need to be an additional time term t?

I think is an argument passing convention thing...have you done any programming?

I know that as a human, you can easily see that x depends on time t, but if you call a function V() and you only pass the x, y and z functions (of time) and do no pass the time...how is the function V() supposed to know what time to evaluate the functions x(), y(), z()? And so, you need to pass the scalar t, as well.

I think is an argument passing convention thing...have you done any programming?

I know that as a human, you can easily see that x depends on time t, but if you call a function V() and you only pass the x, y and z functions (of time) and do no pass the time...how is the function V() supposed to know what time to evaluate the functions x(), y(), z()? And so, you need to pass the scalar t, as well.
I just...I don't even...Have you ever so far as to even go want if look more like?

Last edited:
sophiecentaur
Gold Member
I don't think you need a 't' in the brackets for all cases - for instance, where there is no acceleration. But, in general, the velocities may not be constant at all points x,y,z - so you need to specify the velocities at all points as they vary with time..

ha!...I really lost you or you really never followed.

o.k. another shot at it.

If V() depends on x() and x() depends on t...does V() depend on t?

And so, when you write the signature of a function, you need to include in its parameter list all the parameters it depends on...and so V=V(x,y,z,t)