The Porsche vs Ferrari (or Badger vs brielga) thread - Page 424 - 10-Tenths Motorsport Forum

arakis · 11 Jul 2012, 09:35

Quote:

Originally Posted by Dario911

If we consider two cars, both with the same aerodynamic, transmission, engine, ecc. the final top speed will be higher for the heavier one, according to F=ma formula. We were only talking about weight influence.
Anyway, it's obvious a=F/m make the heavier car slower to reach its top speed, but I've said the same. But terminal speed is a physics concept.
A car's terminal velocity is similar to it's maximum speed.
As car's start to accelerate there is more force pushing the car forward than there is air resistance slowing the car down.
As the car's speed increases so does the air resistance, eventually the force of the air resistance will equal the the force of the car's acceleration.
At this point the car can no longer accelerate, it has reached it's terminal velocity.
That's physics.

NO and NO, you are plain wrong...Force is the same as the only force pusing the car is the ENGINE..

in the vertical drop the Frce actigng on two objects is the gravitational pull from earth(Me), and the object(Mo)
gravitational force is calculated as Fg=G*(Mg*Mo)/r^2
G is the gravitational constant!

and acceleration is a=Fg/Mo if you connect the two formulas you get a=(G*Mg)/r^2 which is 9.81-9.83 depending on your location.

the acceleration is constant because the object mass is cancled out by the two formulas, and the acceleration in gravity is only dependent on the Mass of the earth..

In a car driving on a road, there is no gravitation force pushing it forward, only the force of the engine which is constant, and has nothing to do with the mass of the object...

so cars acceleration is a=Ft/M Where Ft are all the forces action on a car(Ft= +EngineF -Roling resistanceF -Windresistance -drivetrain resistance) Fe is constant for the same car with different mass Rolling resistance incresses with Mass

Top speed is achived when there is no more acceleration, all the forces acting on the car have ballanced each other out. Ft=0...
or when EngineF = Rolling resistance + Windresistance + drivetrain resistance
abd because the Rolling resistance for the same speed is higher for a car with higher mass. the engineF has to be higher to reach the same speed.

And since this is not possible, because the engine is the same, a lower top speed will be achieved....

If you do not understand this, I'm sorry, but trust me this is true! continuing to state the opposite, is just embarrassing, as it shows you don't have the basic understanding of physics, which are learned in elementary school, and further studied at high-school...

Spyderman · 11 Jul 2012, 10:13

Not a physics man myself, but this is an interesting read: http://www.physforum.com/index.php?showtopic=14909

Richard Casto · 11 Jul 2012, 18:29

Quote:

Originally Posted by Dario911

If we consider two cars, both with the same aerodynamic, transmission, engine, ecc. the final top speed will be higher for the heavier one, according to F=ma formula. We were only talking about weight influence.
Anyway, it's obvious a=F/m make the heavier car slower to reach its top speed, but I've said the same. But terminal speed is a physics concept.
A car's terminal velocity is similar to it's maximum speed.
As car's start to accelerate there is more force pushing the car forward than there is air resistance slowing the car down.
As the car's speed increases so does the air resistance, eventually the force of the air resistance will equal the the force of the car's acceleration.
At this point the car can no longer accelerate, it has reached it's terminal velocity.
That's physics.

Create a "free body diagram" that shows the forces involved. At it simplest (which is what I suggest you do), include only the aerodynamic forces and the driving force from the powertrain (engine, transmission, etc.) and ignore things like mechanical friction losses (rolling resistance, powertrain power loss). Those two forces would oppose each other. This explains how to create a free body diagram...

http://en.wikipedia.org/wiki/Free_body_diagram

I am not sure, but I think you seem to understand that we are talking about regarding the free body diagram because when the two forces are equal, there is no acceleration, the speed is now constant and at the maximum value.

So with the powertrain force (one 1/2 of the force in the free body diagram) you would agree that you can remove the engine, transmission, etc. from the vehicale (so you take the overall weight of the vehicle out of the equation) and you can now measure it via a dynometer. And that regardless of how heavy the vehicle is that the force provided would remain the same. Would you agree?

Now you look at the aerodynamic forces (the other 1/2 of the force in the free body diagram). Use the following links to see to calculate that value...

http://en.wikipedia.org/wiki/Drag_equation
http://en.wikipedia.org/wiki/Drag_coefficient

The key is the drag equation of ...

F = 1/2 pv^2CdA

This involves things like the drag coefficient of the vehicle, frontal cross sectional area of the vehicle, speed of the vehicle and density of the fluid (air).

You will note that the mass of the vehicle is not part of the above equation. This means vehicle mass does not impact either the amount of aerodynamic drag or the amount of force that the powertrain can deliver. It has no impact on top speed.

So while "F=ma" (Newton's second law) is true, "F = 1/2 pv^2CdA" (fluid dynamics drag equation) is also true. You just have to use the right equation for the right problem. I could try to stuff pythagorean theorem into this problem and while it is a valid formula, it is the wrong one for the problem.

I have suggested you follow the math earlier, but you don't want to do that. I and others have provided specific equations and examples and have explained how you are doing this wrong. If you don't want to follow the math then consider some other examples that use your logic, but you might agree don't work. If increased mass allows for higher top speed, wouldn't long distance runners, wear weight belts to increase their top speed and pass other runners? For high speed trains, couldn't you just keep adding more and more weight and the trains would go faster and faster all on their own? If a train was at maximum speed and a bird landed on top (increasing the overall weight) would the train suddenly speed up? If you made an object infinitely heavy, would it go infinitely fast even with a small engine?

Beyond this, I doubt anyone on this forum will be able to convince you otherwise. I suggest that you find a physics instructor that you will believe their option and ask them. As entertaining as it is to have this discussion, I think I am repeating myself, so I may bow out.

Quote:

Originally Posted by Spyderman

Not a physics man myself, but this is an interesting read: http://www.physforum.com/index.php?showtopic=14909

Thanks for the link. I read through the thread and in short they reach the same conclusion that all things being equal, mass does not impact top speed. If you include impacts of rolling resistances, etc. then higher mass will increase mechanical drag which will reduce top speed. I do agree that a heavier object will be more stable and maybe easier to drive at top speed than an equal car that weighs less. But it will not increase it's top speed.

Richard

**Adam43** · 11 Jul 2012, 18:41

Yep, everything else being equal mass does not change the terminal speed, just how quickly you get to it.

In the F=ma equation quoted above. In this case considered here F remains constant and defined by the powertrain. Increase m and you don't increase F, you decrease a. As said above.

Dr Adam 43 (phd in Physics).

Spyderman · 11 Jul 2012, 20:35

..But this is exactly what some of us were saying. Weight does not have much of an impact on top speed. It affect acceleration, breaking, handling, tire ware, but not significantly top speed.

**Adam43** · 11 Jul 2012, 21:01

Quote:

Originally Posted by Spyderman

..But this is exactly what some of us were saying.

Just to clarify, if it is needed, I was merely agreeing and adding to the consensus.
(confused by the "But" part)

arakis · 11 Jul 2012, 21:42

I agree that it does not effect by much, but it does effect it trough rolling resistance, and drive train losses, but these numbers are indeed negligible..
But higher mass certainly doesn't give a car a higher top speed, that makes no sense at all...

Articus · 11 Jul 2012, 23:07

Porsche vs Ferrari they said...

Spyderman · 12 Jul 2012, 06:47

Quote:

Originally Posted by Adam43

Just to clarify, if it is needed, I was merely agreeing and adding to the consensus.
(confused by the "But" part)

Sorry about the confusion. Somehow the argument got twisted, and those that were originally arguing that weight did not have a significant effect on top speed somehow got placed in the camp that were defending that weight effected it greatly.