# Primitive variables in Fluid Mechanics

## Main Question or Discussion Point

Hello!
I know that the primitive variables in fluid mechanics are velocity and pressure. But why?
I don't see how "primitive" these variables are...What does it mean by a "primitive variable"? Is that all other variables in a fluid flow can be derived from velocity and pressure? Is there any other set of primitive variable? Lastly, how do you know velocity and pressure are primituve variables?

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I am not aware of such terminology but they are the main variables. You can manage any fluid flow problem if you know these two things.

quark, thanks! I was afarid that no one is going to help me out. Why can we manage all flow problems if we know these 2 things?

hanson said:
Hello!
I know that the primitive variables in fluid mechanics are velocity and pressure. But why?
I don't see how "primitive" these variables are...What does it mean by a "primitive variable"? Is that all other variables in a fluid flow can be derived from velocity and pressure? Is there any other set of primitive variable? Lastly, how do you know velocity and pressure are primituve variables?
Try this ....
When you try to solve a fluid feild without energy equation (heat transfer)? Conservation of mass and Conservation of momentum (Derived from Newton's Second law) are sufficient. You will find the main variables are pressure and velocity. With pressure and velocity information you can find the fluid feild. BESIDES all the properties.

QUOTE=hanson;752113]Hello!
I know that the primitive variables in fluid mechanics are velocity and pressure. But why?
I don't see how "primitive" these variables are...What does it mean by a "primitive variable"? Is that all other variables in a fluid flow can be derived from velocity and pressure? Is there any other set of primitive variable? Lastly, how do you know velocity and pressure are primituve variables?[/QUOTE][/FONT][/SIZE]

what is primitive variable? i know it is velocity and pressure,but why it is? Is that all other variables in a fluid flow can be derived from velocity and pressure?

minger