I would like to find a formula which is simple, not all that accurate
scientifically, and delivers straight forward results and puts into
account the weight, speed, how aerodynamic is the body in three types
for example.  That being very aerodynamic, aerodynamic and not all
that aerodynamic.

The parameters might be:

1. Stationary weight
2. Speed in Km/h
3. Aerodynamic register (1, 2 or 3 for example)

The result would be the weight of the car at its indicated speed.

I would be able to use a spread sheet program as well to arrive at a
what-if scenario where I might want to know at what speed a car has to
be in order for it to at a certain weight.

Thank you.

-Dusty

---

Request for Question Clarification by pafalafa-ga on 14 Oct 2003 18:16 PDT

Hi there,

Maybe I'm way off here, but as far as I know, a car's weight is its
weight...period.  Unless you change the force of gravity by, say,
putting it on the moon, it's weight is pretty much a constant.

Take the example of a 10,000 pound airplane.  It weighs 10,000 pounds
whether it's sitting on the runway, taxiing at 150 mph, or flying at
600 miles per hour.

I don't think the speed or aerodynamic shape makes a bit of
difference.

Can you tell us a bit more about what it is you're after here...maybe
one of us will be able to assist you.

Thanks.

---

Request for Question Clarification by mvguy-ga on 14 Oct 2003 20:31 PDT

Are you possibly talking about something related to momentum rather
than weight per se? For example, a one-ton car that hits you at 60 mph
will do the same amount of damage as a six-ton car traveling at 10
mph, or something like that. Is that the concept you're looking for?

---

Clarification of Question by dustydune-ga on 15 Oct 2003 11:15 PDT

Uh! :-)

I've pulled you all into a wild goose chase and I'm sorry for that and
it's due to my lack of ability to express myself clearly.

I don't know what you would call it, but the weight of a high speed
car on the pavement to me would logically be less than that of a
stationary one in terms of how much weight that pavement would need to
support have a 1 ton car pass over it at 150 Km/H compared to it
passing over at at 5 Km/H.

Take an area that would be under both front and then back wheels of
that vehicle when it passes by and put a scale of sorts under it. 
Would it register 1 tons of weight from that 1 ton car passing by at
150 km/H and also register the same weight when it passes by at 5
Km/H?

The above I'm sure have appropriate physics terms to express them, but
I'm not aware of them nor was my early or later education in English
to come up with the right terms. :-)

Hope someone can help me out?

-Dusty

Hello and thank you for your question.

Luckily for you and me, Isaac Newton asked and answered questions like
these so we have his footsteps to follow.  (Before Newton, Aristotle
had also considered these issues, and experimental science has since
shown Newton's analysis to be better than Aristotle's in describing
what really happens to an object in motion.)

A key concept here is the 'normal force.'

"The term normal in mathematics means perpendicular. If an object is
in contact with a surface, the surface exerts a force on the object
called a normal force. It is perpendicular to the surface ... and
directed away from the surface the object is on. In general, we must
solve Newton's Second Law to obtain the value of the normal force for
our particular situation.
Example 1: A 500 N crate rests on a horizontal floor. Although this is
a trivial case, we will use the Second Law to calculate the normal
force to demonstrate how the calculation is done. In the vertical
direction ... [t]here are two forces acting on the crate: the downward
force of its weight, and also the upward normal force.... [The crate
weighs 500 N and] the floor pushes back with a normal force equal to
500 N. In this case it is directed upward because the floor is
horizontal."
Newton's Laws of Motion
http://www.bill-johanson.com/111s03/ch4.shtml

So your question is, does a sideways motion of the object make any
change to the normal force, i.e. the force that the road exerts on the
car which as seen above is equal in magnitude to the weight of the
car.

If the 'car' is an airplane rolling down a runway, the answer is yes,
as the plane starts to lift off its weight on the ground starts to
decrease.  But that's an aerodynamic effect caused by the way its
wings interact with the rushing airstream.  Chop the wings off the
plane and eliminate all other sources of airlift caused by the
particular shape of the vehicle (or roll your vehicle wings-and-all
down the runway but do so in a vacuum) and the answer is no, the plane
rolls and rolls, there's no lift, and its weight remains constant.

So if the road is level and in the absence of any lift caused by air
resistance, the weight stays the same.  I mention the road being level
because if the road slopes up or down then that's another reason the
weight might change.  Accelerate up a hill and you'll sink into the
cushions because your weight like the weight of the car has increased;
accelerate down a hill and the pit of your stomach will tell you that
your weight like the weight of the car has decreased (going up and
down slope also complicates how the normal force is calculated).

Search terms used:
newton's laws  "normal force" "at rest"  weight
://www.google.com/search?q=newton%27s+laws++%22normal+force%22+%22at+rest%22++weight&hl=en&lr=&ie=UTF-8&oe=UTF-8&c2coff=1&safe=off&start=10&sa=N

Thanks again for bringing us your question.  Try the Google search
given above and you'll find lots more to read on the subject.

Sincerely,
Google Answers Researcher
Richard-ga

---

Clarification of Answer by richard-ga on 15 Oct 2003 12:22 PDT

In rereading your question, I noticed you asked specifically for a
mathematical formula.

In my answer, for the sake of clarity I edited the quoted excerpt to
remove its fomulas.
http://www.bill-johanson.com/111s03/ch4.shtml 

They're on that page if you still want them!

-R

Hello

Well the wight (mass) of the car is always the same at any speed (
Average speeds on earth, if we come closer to the speed of light then
e=mc²).
Now the drag doesn´t affect mass from the car but the aerodynamic
effect can alter the wight on the road.
Some cars get a drag lift and so they are "lighter" and some cars get
pressure drag and get "heavier".
This thing is called downforce and prevents that automobiles get
airborne ;)

For example formula 1 race cars can add much more downforce then they
actually wight.


Some car manufactores give exact data how much lift you have at a
certain speed. For example Porsche states different numbers for there
different versions from the basically same body. As

downforce costs power & speed the aerodynamic has to be balanced for
the cars purposes.
Those datas are sometimes puplished in spreadsheet form.
Also the german car magazine Sport Auto runs a "Supertest" series
where they actually messure

the candidates in the old Mercedes Benz or FKFS Windtunnel.


Now some links:

http://autozine.kyul.net/technical_school/aero/tech_aero.htm#Drag and
Lift ( Marc Wan is always

a good source )
http://www.trackaero.com/factors1.html
http://www.mustangsandmore.com/ubb/DanJonesTorqueVsHP.html
://www.google.de/search?q=cache:9TediwvN62EJ:www.phys.unsw.edu.au/hsc/moving.ppt+aerodynamic

+drag+mass+weight&hl=de&ie=UTF-8

An other good source is Autospeed in australia:
http://www.autospeed.com/A_1044/cms/article.html
http://www.autospeed.com/A_1055/cms/article.html
http://www.autospeed.com/A_1065/cms/article.html
http://www.autospeed.com/A_1071/cms/article.html
http://www.autospeed.com/A_1080/cms/article.html

http://www.autospeed.com/A_1094/cms/article.html
http://www.autospeed.com/A_1538/cms/article.html
http://www.autospeed.com/A_1784/cms/article.html


Online Drag-calculators:

http://davewin.com/tech/horsepower_calc.shtml
http://www.eng.vt.edu/fluids/msc/jscalc/cdcal26.htm
http://www.windpower.org/en/tour/wtrb/dragrace.htm 

This isn´t a dragcalculator except for american drag racing ;)
http://kowboy1.bananaman.com/xycool/dragperf.html

Unfortunatly sport-auto online changed dramatically so the only source
aviable is:
In this picture you will find the actuall messurements including
forces on the left side in the

middle:
http://www.honda-s2000.de/05archiv/presse/0011_spa/28-29_gr.jpg
here is the intropage to the complete article
http://www.honda-s2000.de/05archiv/presse/0011_spa/0011_spa.html

Here is the link to the FKFS 
http://www.fkfs.de/veranstaltungen/euromotor2004/scope.htm
http://www.fkfs.de/windkanal/windkanal_uebersicht.htm

A link to maybe the most comphrehensive technial board in automotive:
http://forums.atlasf1.com/forumdisplay.php?s=&forumid=8 

Relatet Topics:
http://forums.atlasf1.com/showthread.php?s=&threadid=26926 
http://forums.atlasf1.com/showthread.php?s=&threadid=52708 
http://forums.atlasf1.com/showthread.php?s=&threadid=31486 
http://forums.atlasf1.com/showthread.php?s=&threadid=41387 
http://forums.atlasf1.com/showthread.php?s=&threadid=61971 

Grüsse

I mya be wrong but I think Dusty wants to know a little about the
effect the car has on the ground, i.e the damamge it may do to the
road. THis is related to weight but not the same. On a firm surface
that is capable of supporting the weight of the car indefinitely, i.e
pushing back with an equal and opposite force, it makes no difference
whether the car is moving or not, assuming a level road. However if
the surface is spongey, e.g. mud, the surface fails to support the car
and the car sinks. If the stretch of mud is only short, then the
faster the car goes, the less time it has to sink in - this is where
speed becomes a factor. But on an infinite stretch of mud the car will
surely sink down at the same rate as if it were stationary - except
for the effect of fluid dynamics that will have a bearing and I know
nothing about.
Heavy lorries damage road surfaces by travelling over them at speed
but this may have a cause in the vibration and shockwaves they set up.