What brings acceleration???

[pompelmo]

There are 2 things we look about an engine, that is torque and power..So, what of those two things gives the car acceleration?? Most of you will say Power, torque brings pull..I'm a physic and i'm saying torque nad also power...i'm a bit confused..there must be some logical explenation..

[MrT]

The torque transmitted from the engine to the wheels, produces the forward force at the contact patch. This force drives the vehicle forward and hence produces the acceleration. Power is just a function of torque as it is just the rate of doing work.

Power = work done / time
Power = Work done / (1 / RPM)
Power = Torque * RPM

[pRo]

You need to know the power OR torque curve of any given engine, to actually calculate anything. Peak power or peak torque tells very little or nothing.

Like MrT said, the other can be calculated from the other. Here's the formula with a constant for "familiar" units:
Power (hp) = Torque (ft-lb) * RPM / 5252

[pompelmo]

Power = work done / time
Power = Work done / (1 / RPM)
Power = Torque * RPM

this is more "high school" stuff..i need more scientefic proof!
F1 car has almost the same torque as a street car (powerfull) and it has greater acc....why? (don't tell me about weight)

[pRo]

No offense, but if you're a physic, as you say, you must be able to figure out what causes acceleration and why two cars with equal torque can have VERY different acceleration...?

Some cars do have variable transmissions, where the engine is kept at power or torque peak all the time. F1 cars don't have them. Now you can do the math yourself.

[pRo]

Sorry about the harsh reply.

I've posted here to explain the difference between torque and horsepower, please read it, maybe it helps to explain some things:
viewtopic.php?p=36475

[basrawi]

The 2006 F1 cars have a power-to-weight ratio of 1250 hp/tonne (930 W/kg). Theoretically this would allow the car to reach 100 km/h in less than 1 second. However the massive power cannot be converted to motion at low speeds due to traction loss, and the usual figure is 2 seconds to reach 100 km/h. After about 130 km/h traction loss is minimal due to the combined effect of the car moving faster and the downforce, hence the car continues accelerating at a very high rate. The figures are (for the 2005 Renault R25):

0 to 100 km/h: 1.9 seconds
0 to 200 km/h: 3.9 seconds
0 to 300 km/h: 8.4 seconds, may be slightly more or less depending on the aerodynamic setup.

AND it is all about power-to-weight ratio, I was searching for the relation between torque and acceleration, i didn’t find any,,, they always relate the acceleration to the power-to-weight ratio.

Its an interesting subject, ill search more for answers.

[basrawi]

thats it this site will explain it all http://craig.backfire.ca/pages/autos/horsepower

[Ciro Pabón]

There are 2 things we look about an engine, that is torque and power..So, what of those two things gives the car acceleration?? ...

Both of them, pompelmo, both of them.

For the physicist in you:

- For a rotating object, the power needed to stop it is the integral of the torque with respect to rpm (the area under the torque-rpm curve).

- For a moving object, the power needed to accelerate it is the double integral of power with respect to time and space.

If this seems like high school physics, perhaps is because it is.

pRo posted something very similar today. Maybe both threads could be as ebony and ivory on my piano (or torque and rpm on my power) and become one.

There are numerous calculators that give you power once you assume mass, initial speed and final speed. My pathetic Excel version is here.

[MrT]

It's not high school stuff... its basic physics which is still applicable! It fundemental to the understanding! Those equations underline the basics.... We used those equations throughout the Motorsports engineering degree i have just completed. Work everything from first principals!

[/quote]

[Carlos]

Excuse me if I intrude. The basic principle if all activity is civility. I am just too fragile for the "tone" of this discussion.

[Gecko]

I am sorry, Ciro, but the integrals you mention make no sense. The power needed to stop a rotating object can be arbitrary (it just takes longer with less power), and the actual energy needed depends only on the moment of ineria and the angular velocity of the object. And for a moving object, how can the expression for power depend on power itself (not to mention that even the basic units are wrong)?

[Ciro Pabón]

I am sorry, Ciro, but the integrals you mention make no sense. The power needed to stop a rotating object can be arbitrary (it just takes longer with less power), and the actual energy needed depends only on the moment of ineria and the angular velocity of the object. And for a moving object, how can the expression for power depend on power itself (not to mention that even the basic units are wrong)?

You are right, Gecko. I tried to cut and paste from another thread by pRo and, when I couldn't, I ended writing it again in a hurry. I think, from the top of my head that the integrals are like this:

- For a rotating object, the power you can use from its energy is the integral of the torque with respect to rpm.

- For a moving object, the power needed to accelerate is the double integral of acceleration with respect to time and space.

Besides, you are right spotting another error: it is the energy needed to stop a rotating object what is constant.

Anyway, I haven't had the time today to write the equations. Until I do (or I get "Vehicle dynamics" from my office) I might well have made another mistake. Sorry, this is what happens when you "don't do your homework". Would you believe me I say I've been really busy today and I am trying to distract myself a little between recalculations being made in my computer?