Explain me some physics

[detail]

I remember that at high-school for 4.5 (of 5) years of physics I had A marks, but now I forgot many things and need an explanation of such a simple question.

So, the friction coefficient for rubber and asphault is about 0.3-0.35, at least less than 1. But how is it possible to achieve lateral and longtual acceleration of more than 1g, without downforce? (which means that friction force is stronger than gravity) Or even with downforce, FV8 makes 3g lateral acceleration (3g/0.33 = 1g (own weight) + 8g (downforce)!) Where is the mistake?

[colcob]

Where did you read that the friction co-eff for rubber/asphalt is .35?

Either way, the model of friction you get taught in high school is incredibly basic, (called Coloumb Friction if memory serves) and only applies to notionally rigid bodies ( so Coloumb friction works pretty well maybe for railroad wheels on steel tracks).

But if the Grip = Mu*Load equation held up in the real world, then trucks could drive around on a set of 4 180mm wide hatchback tyres and have just as much lateral grip as any other vehicle.

In reality, rubber on asphalt acheives its grip in two ways, one called hysteresis, which i dont pretend to understand but is to do with the way the contact patch deforms under load (which is not the case if you just took a solid block of rubber and rubbed it against some asphalt).
And secondly adhesion, which is basically stickiness. The molecules of the rubber stretch and interlock with the molcules of the road surface, like microscopic velcro. And this effect is larger with softer stickier tyres and higher temperatures.

So G forces higher than 1 in non aero cars are acheived by effectively 'sticking' to the road, rather than just resting on it in the traditional friction model, and in aero cars higher G forces are acheived because even though your Mu might only be 1.3, the load on the tyre is no longer proportional to the mass of the car because of the aero load, so the grip force can be much higher.
But as this force is still only accelerating the same mass, the rate of that acceleration is much higher.

[detail]

Agh, all right, thanks a lot! That formula 3/.33 = 1 + 8 was told me by a guy who tried to convince me (basing on the simple formula) that F1 produces 10 tons of downforce. I didn't beleive. Thanks!

[GP4Flo]

I just took a look at my physics book and it also has a friction coefficient of 0.3 for car tyres on asphalt and 0.15 for a wet surface. There is a note, that this only applies if the car isn't moving.

[Fonnybone]

I just took a look at my physics book and it also has a friction coefficient of 0.3 for car tyres on asphalt and 0.15 for a wet surface. There is a note, that this only applies if the car isn't moving.

l0l, isn't this the infamous low-speed grip problem in LFS ? Mmmm
Btw, very interesting post there Colcob, 'physics101' teach you that
Coloumb thing alright, i had to do it a few years ago.

[Bob Smith]

But if the Grip = Mu*Load equation held up in the real world, then trucks could drive around on a set of 4 180mm wide hatchback tyres and have just as much lateral grip as any other vehicle.
But it does doesn't it? It's just that Mu is a function of load (among other things), so you almost expand out the equation if there was a perfect formula for Mu. Unless you just leave Mu as a constant the equation works fine.

And with uber tyres on a truck and really bad ones on a hatchback there's no reason why they wouldn't corner at the same speed. Though you did say the same tyres, so I can't pick at that bit. :)

[colcob]

Yeah, I meant the static value given in the textbooks, obviously.

[Don Merino]

a guy who tried to convince me (...) that F1 produces 10 tons of downforce.
Did he ever wonder how its suspension and wheels would take those 10 tons?

[Hallen]

Did he ever wonder how its suspension and wheels would take those 10 tons?


:doh: Never let logic stand in the way of a perfectly good fantasy :ices_rofl

[qwejibo]

F1 cars probably make about 1500-2000kg downforce(max speed), I think?

[Fonnybone]

What about 10g? Seeing how everyone these days likes to throw 'g'
all over the place, maybe he mixed up 10g with 10tons. 'G' could be
mistaken for a 1000 as used by anglos, "I got 2'g' in my wallet".
1000kg is one metric ton. 'G', 'ton' ....

Nevermind me, i just woke up...:sleep2:

[Eldanor]

Sorry, I missed the thread :(