Merv the Derv

...im no rocket scientist, but fan of physics:

heres a good definition, anyone want to do the math

"....it's really an approximate equation for terminal speed (I say speed because velocity describes both speed and direction).

The two dominant forces in free-falling through the atmosphere are drag and
gravity. (Atmospheric) Drag is due to what we call (skin or surface)
friction. Long story short, the typical formula for atmospheric drag is

D = (1/2)*C*A*p*(V^2)

D is the drag force, in Newtons (or pounds)
C is the coefficient of drag, or drag coefficient, which is unitless
C is often written as Cd where "d" is a subscript
A is the area of the body's surface over which the air is flowing
p is the density of the air, in kg/(m^3) or slugs per cubic foot
V is the speed of the air flow relative to the body which is experiencing
the drag
V is expressed in meters per second (m/s) or feet per second

The units for D is then ( kg/(m^3) * (m^2) * (m/s)^2 ) = kg*m/(s^2) =
Newtons
or ( slugs/(ft^3) * (ft^2) * (ft/s)^2 ) = slugs*ft/(s^2) = pounds

note: a slug is the imperial unit for mass, just like the kilogram (kg) is
the SI unit for mass

note: the density of air is not constant, it changes over time and
location. You can read more about this in the references, below.

The force exerted by gravity is called weight. The formula is

W = m*g

W is the weight, in Newtons (or pounds)
m is the mass of the object, in kg (or slugs)
g is the acceleration due to gravity, in m/(s^2) (or ft/(s^2))

note: I'm using the carat "^" for exponentiation. a^b is "a" raised to the
power of "b", so that 2^2 is 4, 4^2 is 16

note: acceleration due to gravity changes with location. This is often
ignored for problems like what you're describing, but if you double your
distance from the center of Earth, then the acceleration due to gravity is
one-fourth what you felt before.

If there were no atmosphere to slow you down, the force of gravity would
continually accelerate you until you collide with something solid (like the
earth). However, the atmosphere does exists and it retards your motion
with the force of drag. Therefore, the resultant force you feel towards
the earth is weight minus drag (W-D) and when your speed increases to the
point that the drag you feel equals your weight, you will accelerate no
more. This then, is your terminal speed. And the equation to find it is:

W = D
m*g = (1/2)*C*A*p*(V^2)

and we can rearrange this with some algebraic manipulation to get

V^2 = 2*m*g/(C*A*p)
or
V = ( 2*m*g/(C*A*p) )^(1/2)"

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And I always thought you used algebra to reduce excitment whilst on the job. How stupid of me!

znod

His car really is slow since, as I recall, it takes a sky diver about 10 secs. to accelerate to a terminal velocity of about 120 MPH when in "standard" sky diving position.

BetterMakeWay

His car really is slow since, as I recall, it takes a sky diver about 10 secs. to accelerate to a terminal velocity of about 120 MPH when in "standard" sky diving position.
[/quote]
So? It doesn't mean it's not fun...remember weight has a word to say and on twisties it means quick times and lots of fun AND it's still a bmw...an e60 if i'm not mistaken

m630

LMAO

znod

His car really is slow since, as I recall, it takes a sky diver about 10 secs. to accelerate to a terminal velocity of about 120 MPH when in "standard" sky diving position.
[/quote]
So? It doesn't mean it's not fun...remember weight has a word to say and on twisties it means quick times and lots of fun AND it's still a bmw...an e60 if i'm not mistaken
[/quote]Yes, it must be very light if it can't beat a sky diver to 120 MPH. ~(;^) And, you are right it still is a great car no matter how fast it gets to 62 MPH.

Shebs

Thanks for your gentle comments, you were of great help really and you showed your great knowledge about cars in general .

I did expect people like you making fun of my 520i, but it's ok. I like the car, it is fun to drive. Also, I will be glad to overtake you on any curve due to the the lower weight in front and the better front to rear weight distribution in my car .

And by the way, due to customs and tax issues in Egypt, my 520i costs more than your 545i (my car costs exactly $81,000), so please give me a break.

I never said I was doing neutral drops, but anyways if you want to come to Cairo I'd be happy to be your host (that is if you are ever able to get out of Arkansas). Also, you don't have to return my transmission, I have a lot of friends to do that for me, I won't be waiting for you .

It seems that due to your immense knowledge about the world, you've confused Egypt with other Middle East countries, oil is not the major contributor to the Egyptian economy due to it's scarcity. So you will never visit a rig in Egypt, especially around Cairo as you stated .

fred1976

Just a comment on this thread : how do you measure the time?

I suppose that the best way to obtain a good time is to use a kind of automatic chronometer that stops exactly at 100km/h.

If the time data you provide are realised "manually", meaning you press start and stop, then I suppose you should take into account a human error coefficient (you cannot get as my opinion an accuracy of data of 0.1s when looking at the road and the tachymeter alternatively because this action costs you much more time) and also the neural transmission delay supposing that you have overcome the first problem in any (unknown) way.

Thias said, I suppose you were maybe to pessimistic and in fact your car is maybe having the announced measurements! The best solution is, for me, to forget about this and just have fun with your car when you press the gaz and be pressed against the seat!

m630

Thanks for your gentle comments, you were of great help really and you showed your great knowledge about cars in general .

I did expect people like you making fun of my 520i, but it's ok. I like the car, it is fun to drive. Also, I will be glad to overtake you on any curve due to the the lower weight in front and the better front to rear weight distribution in my car .

And by the way, due to customs and tax issues in Egypt, my 520i costs more than your 545i (my car costs exactly $81,000), so please give me a break.


[/quote]

..now now now Shebs, please dont take offense, we were only joking ..im personally looking to get the 530i so im just playing here,...all E60s are great cars and wouldnt put any other owners car down!

KYRIACOS

And by the way, due to customs and tax issues in Egypt, my 520i costs more than your 545i (my car costs exactly $81,000), so please give me a break.

Mine cost $91,000 here in Cyprus (total rip off) but still a great car to drive!!!!

Shebs

Oh my god! That is a total total rip off. I thought my 520i was the most expensive around the world. Welcome to the Mediterannean sea countries .