Drag...

09-05-2007, 04:49 PM

I know i asked about gravity and a little about drag in my last thread, but this is in entirety about drag and drag concepts...

1. What is Unit vector and how do i calculate it?
2. What is the reference area of an object and/or how is it calculated (is it just 2-D area or such)
3. "v is the speed of the object relative to the fluid,", does this mean that is the fluid is traveling at 10 mph and my obj is traveling with the fluid at 15 mph, its 'v' is 5?
4. Barometric formula, how do i use this to calculate pressure (IE; explain pascals, kelvin, Molar mass of Earth's air (28.9644 g/mol) (what is g/mol and how does it play in the equation), lapse rate, ect.)
5. How is wind that is resisting, turning (ie, wind coming from the right pushing it left), aiding (coming from behind) calculated?

Any help would be EXTREMELY appreciated, please try to explain the quests seperately and in simple, yet detailed methods. Thank you in advance.

09-05-2007, 05:17 PM

Alexander244

A 3-dimensional vector is made of 3 components; x, y and z. A unit vector is a vector with length 1. You can calculate it by dividing each component by the total length of the vector.
?
If v is velocity relative to the fluid, yes :)
Pascal is a measure of pressure (1 newton per square meter)
Molar mass is the mass of one mole of a compound. i.e. 1 mol of air = 28.9g
Kelvin = Celcius + 273.15
Not sure about the other stuff.
Not really sure what you are asking... Get the vector of the wind, then use it as a force.

09-05-2007, 06:00 PM

moyack

about the fifth point, you could have a good approximation in this way: the resistance of the air is proportional to the speed of the object.

Fwind = K * Vobject (where K is a constant that you define according to experiments, as far as I remember, I'm not sure, it depends of the air density and other stuff.)

And because the air puts resistance, the vector should be in a direction opposite to the movement (ie. A parachute has this kind of resistance)