rec.autos.simulators

F1RS ??

Paul Godfre

F1RS ??

by Paul Godfre » Sat, 09 May 1998 04:00:00

I'm have to reply to this common misconception. touching the grass at
200mph (or whatever speed) will not "speed you up". It is not physically
possible, unless some force is applied to increase the speed, it cannot
happen (ie. staying on the throttle would provide such a force, but even
then you will speed up less than you would if you had stayed on the
pavement due to the reduced friction coefficient of the tires on the
grass relative to the pavement). Don't get mixed up - more friction is
good between the tires and road (rolling resistance, however, is
detrimental to speed), but air friction produces the majority of drag at
any speed over approx 30mph. To return to the elementary laws of
physics, a body in motion stayes in motion unless acted upon by a force.
So, a car would continue in a straight line at a constant speed forever
were it not for the external forces of surface friction (simple rolling
resistance, steering input, acceleration through throttle application,
etc.), air friction (drag), and other inherent forces. a car WILL NOT
ACCELERATE SIMPLY BY CHANGING THE SURFACE FROM ASPHALT TO GRASS, even
though the silly anouncers (some even former drivers) continue to spout
this "fact". It defies all laws of physics as I've learned them, and
I've had more physics courses than I care to remember.

Now, I think that the perception of increased speed from the***pit is
due to the reduced control experienced when changing from a high
friction surface (asphalt) to a low friction surface (grass). A driver
equates loss of control to "going too fast", ie. when going through a

tires on asphalt was not equal to the centripetal force pushing the car

on the grass, friction is reduced, hence control is reduced, hence,
perhaps to some???, a perception of increased speed (ie.
all-hell-breaking-loose ->ie. increased speed). This is just my personal
attempt to explain why SOME drivers claim that the speed increases on
grass. I GUARANTEE YOU, measure the speed of the car before it leaves
the pavement and continue monitoring while on the grass - the speed
won't increase unless the driver has complete control of the situation
and keeps the car in a straight line with the throttle applied, and then
the increase in inferior to that which could occur on the higher
friction surface of the asphalt. You see, we race on asphalt because it
provides a high coefficient of friction between the tire and the road,
hence quicker acceleration, turning response, braking, etc. Take a car
travelling 200mph, remove ALL friction, and it will not accelerate nor
decelerate, but rather maintain that exact speed and direction, forever.

Anyone with a rudimentary understanding of physics will see that the
statement of a car accelerating "on the grass" is an utterly false
statement.

That's all, sorry for boring you, but this should be cleared up
Paul




> % >
> % > The grass (if one is only just
> % > touching it) isn't going to slow you down, in fact (unless it's really
> % > tall grass), it will actually speed you up.  This is because you loose
> % > grip.

> % Please explain how losing grip speeds you up?

> Believe it or not, even traveling on the tarmac at 200+ mph there is
> friction involved (yep that's the grip).  Now if the car suddenly finds
> its way on a non-grip surface (ice, water, and to some extent grass),
> the friction is gone and the car will speed up.  However, there are some
> down sides to no grip.  Control is certainly one of them, but from a
> certain point the car will actually lose speed, since it can't get grip.

> What doesn't seem to happen in F1RS, is the initial loss of control and
> increased speed when running on grass.  What comes into play almost
> immediately is the fact that the car can't gain/maintain speed that is
> based on grip.  So in a sense, UbiSoft has it half right.

> --
> **************************** Michael E. Carver *************************
>      Upside out, or inside down...False alarm the only game in town.

> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=<[ /./.  [-  < ]>=-=-=-=-=-=-=-=-=-=-=-=-=-=

Jeff Salzma

F1RS ??

by Jeff Salzma » Sat, 09 May 1998 04:00:00

On Fri, 08 May 1998 02:24:22 GMT, Paul Godfrey


>I'm have to reply to this common misconception. touching the grass at
>200mph (or whatever speed) will not "speed you up". It is not physically
>possible, unless some force is applied to increase the speed, it cannot
>happen (ie. staying on the throttle would provide such a force, but even
>then you will speed up less than you would if you had stayed on the
>pavement due to the reduced friction coefficient of the tires on the
>grass relative to the pavement).

        Thank goodness! Somebody was thinking here. Actually, there is
NO change in 'friction' when there's a switch from tarmac to pavement.
There is a significant change in _rolling resistance_ but not
friction. Why? Friction opposes motion, by it's definition.

        Alas, the universe is a quirky place. Where the tyre (tire)
contacts the tarmac, there is no friction. Why? There's no motion! The
speed is zero at the point of contact- trust me on this, it's zero- if
it weren't, it would spin. Yeah, we can bicker for days about the edge
of the contact patch having a different speed, but the truth of it is
that there is no motion between the tyre and the tarmac parallel to
the direction of motion. The only thing friction does is oppose the
spinning tyre, not the car speed. This is why it's easier to pull
something on wheels than a flat box with a *** bottom.

        In fact, the centre/center of the hub/wheel is traveling at
the speed of the car, and the top is double, but that's why the tops
of the tyres wear out faster than the bottoms (groan!)

        Anyway, since there's no motion in that direction, there's no
way the speed can change at all. In a perfect vacuum, that would be
the case. If you put the car, from tarmac to ice, you'd notice no
difference. The rolling resistance might change- OK, I never quite
understood dynamics, I majored in semiconductors- but there's neither
a change in any force, nor any change in (nonexistant) friction. Ergo,
no change in speed.

Jeff

Paul Godfre

F1RS ??

by Paul Godfre » Sat, 09 May 1998 04:00:00


> On Fri, 08 May 1998 02:24:22 GMT, Paul Godfrey

> >I'm have to reply to this common misconception. touching the grass at
> >200mph (or whatever speed) will not "speed you up". It is not physically
> >possible, unless some force is applied to increase the speed, it cannot
> >happen (ie. staying on the throttle would provide such a force, but even
> >then you will speed up less than you would if you had stayed on the
> >pavement due to the reduced friction coefficient of the tires on the
> >grass relative to the pavement).

>         Thank goodness! Somebody was thinking here. Actually, there is
> NO change in 'friction' when there's a switch from tarmac to pavement.
> There is a significant change in _rolling resistance_ but not
> friction. Why? Friction opposes motion, by it's definition.

Pretty good explanation in the part I snipped, but if there were "NO
change in 'friction' when there's a switch from tarmac to pavement",
then a car on the grass would accelerate from a standing start as fast
as a car on pavement. I can assume we all agree that is not true. We
rely on friction between the *** and the pavement to propel the car
forward, not rolling resistance. I do understand where you are coming
from, though - the idea just needs some adjustment/refinement.

Paul

Jeff Salzma

F1RS ??

by Jeff Salzma » Sat, 09 May 1998 04:00:00

On Fri, 08 May 1998 15:23:50 GMT, Paul Godfrey



>> On Fri, 08 May 1998 02:24:22 GMT, Paul Godfrey

>Pretty good explanation in the part I snipped, but if there were "NO
>change in 'friction' when there's a switch from tarmac to pavement",
>then a car on the grass would accelerate from a standing start as fast
>as a car on pavement. I can assume we all agree that is not true. We
>rely on friction between the *** and the pavement to propel the car
>forward, not rolling resistance. I do understand where you are coming
>from, though - the idea just needs some adjustment/refinement.

>Paul

        Err, it's not the same thing. There is no change in friction
because, initially, there is no wheelspin. Accelerating on grass is
'slower' than tarmac, since the grass provides less friction to
prevent wheelspin. In that, you're completely correct, and knowing me,
I didn't explain that correctly.

        Initially, this thread revolved around speeding up when
hopping from tarmac to grass; for that, my explanation is more or less
valid. I hope :)

Jeff

Byron Forbe

F1RS ??

by Byron Forbe » Sun, 10 May 1998 04:00:00


> On Fri, 08 May 1998 02:24:22 GMT, Paul Godfrey

> >I'm have to reply to this common misconception. touching the grass at
> >200mph (or whatever speed) will not "speed you up". It is not physically
> >possible, unless some force is applied to increase the speed, it cannot
> >happen (ie. staying on the throttle would provide such a force, but even
> >then you will speed up less than you would if you had stayed on the
> >pavement due to the reduced friction coefficient of the tires on the
> >grass relative to the pavement).

>         Thank goodness! Somebody was thinking here. Actually, there is
> NO change in 'friction' when there's a switch from tarmac to pavement.
> There is a significant change in _rolling resistance_ but not
> friction. Why? Friction opposes motion, by it's definition.

>         Alas, the universe is a quirky place. Where the tyre (tire)
> contacts the tarmac, there is no friction. Why? There's no motion! The
> speed is zero at the point of contact- trust me on this, it's zero- if
> it weren't, it would spin. Yeah, we can bicker for days about the edge
> of the contact patch having a different speed, but the truth of it is
> that there is no motion between the tyre and the tarmac parallel to
> the direction of motion. The only thing friction does is oppose the
> spinning tyre, not the car speed. This is why it's easier to pull
> something on wheels than a flat box with a *** bottom.

>         In fact, the centre/center of the hub/wheel is traveling at
> the speed of the car, and the top is double, but that's why the tops
> of the tyres wear out faster than the bottoms (groan!)

>         Anyway, since there's no motion in that direction, there's no
> way the speed can change at all. In a perfect vacuum, that would be
> the case. If you put the car, from tarmac to ice, you'd notice no
> difference. The rolling resistance might change- OK, I never quite
> understood dynamics, I majored in semiconductors- but there's neither
> a change in any force, nor any change in (nonexistant) friction. Ergo,
> no change in speed.

> Jeff

   How on earth does a simple case of static friction Vs dynamic friction get so overly
sophisticated to the point of complete confusion?

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