Test Your Knowledge...

OttoNP · Addict Joined: 13 Jan 2003 Posts: 848 City: MI

Okay, I'm bored...

Bob says he just added enough horsepower to his car to go from 0 to 60 MPH in just 1.5 seconds, do you believe him? Why or why not....
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Jim M · Wakeboarder.com Freak Joined: 17 Jan 2003 Posts: 2933

Of course not. It could technically have enough power, but there is no way the car could maintain traction and high torque and actually climb to 60mph in 1.5 secs. Anyone into cars knows that the 0-60 test is poor and very inaccurate. I would like to hear the .25 mile statistics to put things in better perspective.

OttoNP · Addict Joined: 13 Jan 2003 Posts: 848 City: MI

The corresponding quarter mile time would be 6.7 seconds at 119.95 MPH. Also, this is a made up question so bob could have a million horsepower...

Nick
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DockSecret · Addict Joined: 14 Mar 2003 Posts: 756 City: Austin, TX

Wasn't there a highly modified Corvette (twin turbo I believe) that reached 0-60 in less than 2 seconds that was the fastest street legal car Motor Trend ever tested?

Also a 2000 HKS Racing 180SX did 0-60 in 1.2 supposedly. (7.72 sec @ 176 mph)
http://www.fast-autos.net/0to60.html

They won't need a million horsepower... and what is this topic doing in the boats and accessories forum?

wakebrdr190 · Newbie Joined: 17 Mar 2003 Posts: 32 City: MN

i agree with jim, i seriously doubt that "bob" could get the traction needed to hit 60 in that amount of time. unless his gearing is INCREDIBLY low, with bookoo HP and some fat-ass tires.... i dunno...

Breezer · Outlaw Joined: 17 Jan 2003 Posts: 246 City: Austin

A top fuel dragster that runs on nitro methane goes 0-100mph in less than 1 second. That is a fact.

ohsix · Posted: Mar 26, 2003 12:09 pm Post subject:

i was going to say that breezer.
does the answer to bob have something to do with torque being what accelerates his car instead of horsepower?

OttoNP · Addict Joined: 13 Jan 2003 Posts: 848 City: MI

Getting closer...20 minutes left...
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ohsix · Posted: Mar 26, 2003 12:29 pm Post subject:

i'm guessin because torque is a force and force is what accelerates the car. horsepower is the rate at which a device can perform work. i cant remember how to figure horsepower right now and i havent had a physics class in a year so im a little rusty. plus im too lazy to look it up. so someone else answer the question.

OttoNP · Addict Joined: 13 Jan 2003 Posts: 848 City: MI

How fast a car can accelerate is largely dependent on its tires. You can have all the horsepower in the world, but if you don't have any traction your tires will just spin. You can determine the fastest a car can accelerate based on its tire's static coefficient of friction. About the best street tires you can get have a coefficient of 1, which would lead to a 0-60 of about 2.73 seconds. If you hear anything higher than that without special tires it is likely made up. The range for tires goes up to about 4 for dragsters, below is a list of the coefficient and the best 0-60 possible. Also, if you add some kind of downforce or a prop/jet the times will be better.

1 2.73
1.5 1.82
2 1.37
2.5 1.09
3 0.91
3.5 0.78
4 0.68
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ohsix · Posted: Mar 26, 2003 12:58 pm Post subject:

you didnt say he was using street tires or what kind of car he had. jk. i never knew what the coefficient of friction of different types of tires are though.

i did have an argument with a cop one time in physics class because they use the formula: s=square root of 30xfxd. (i dont see a square root button on my keyboard) to determine how fast cars were going before an accident by the skid marks. they will take one of their cruisers and go 30 mph and lock up the brakes to find the coefficient of friction of the pavement and apply that to the other car and he said that formula is proven and accepted in most courts. i argued that the tire compound and weight of the car would also affect the amount of friction but he disagreed. needless to say i still think im smarter than the cop.

noneya · Addict Joined: 13 Jan 2003 Posts: 796 City: Roxboro, NC

There was an article in Car and Driver a few years ago, one of their editors (Csaba Csere i think) got a ticket in a Porsche. He took it to court and PROVED that he couldnt have been going however fast it was given the allowable acceleration distance. Judge said so what and he had to pay anyway!

Geoff Standish · Addict Joined: 13 Jan 2003 Posts: 843 City: Calgary

That modified corvette did it in 2 seconds flat...But it had drag slicks and the rear suspension was sitting almost on the ground. 1.5 seconds seems almost impossible....

Could an all wheel drive car achieve this. Would this make the coefficient 2? and thus make it possible to accelerate at those speeds?

ohsix · Posted: Mar 26, 2003 2:27 pm Post subject:

salmon_tacos · Posted: Mar 26, 2003 4:10 pm Post subject:

Geoff,

AWD will not change the coefficient. The amount of friction, however, is also determined by the pressure on the surface. Simply put, it would be the coefficient * weight / surface area.

If you don't drive the front wheels, the weight on them, which is still part of the mass to be accelerated, is not applied to that friction equation and is lost for the purpose of producing traction.

So anyway...yes, AWD will help. It won't cut times in half though because a lot of the weight shifts back onto the rear tires upon acceleration.

P.S. sorry for sloppy use of "mass", "weight", etc...you know what I mean.

criminally_minded · Posted: Mar 27, 2003 3:23 am Post subject:

Yeah, well I have a friend who has a civic with badass rims and a sweeet exhaust and a honda racing sticker. He can get to 60mph in 3 seconds and does the 1/4 mile in 8. Hes badass. He burns cops and stuff all the time.

uhhhh....... Confused

no.

OttoNP · Addict Joined: 13 Jan 2003 Posts: 848 City: MI

The coefficient is such that that the normal force * it is the max force that can be applied. The normal force is usually the weight but in some cases it can be different, for example on a hill or if you had a spoiler creating additional downforce. There is a static and a dynamic coefficient, the static one which applies before you are sliding/slipping and the dynamic one after sliding/slipping occurs. The dynamic one is usually less than the static one, that's why once your tires break loose it's easier to keep them slipping.
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OttoNP · Addict Joined: 13 Jan 2003 Posts: 848 City: MI

Wes,

In your case with the cops, the right formulas are below:

F=.5*V^2/(G*D)

Where

F is the friction coefficient, V is velocity, G is gravity, and D is skid mark length. If you wanted to use this formula with speed in MPH and D in Feet, it would be:

F=.033404V^2/D

The formula for speed would be:
V=sqroot(2*G*F*D)

If you made this so that you got MPH when you put in feet, it would like like this:
V=sqroot(29.93631*F*D)

Your right about the type of tire changing the F, but I'd guess that most passenger cars are about the same.

Nick
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mcfatty · Addict Joined: 13 Jan 2003 Posts: 725 City: Cookeville

otto

Great post.

I'm sitting at work thinking harder than I have for weeks.

ohsix · Posted: Mar 27, 2003 11:53 am Post subject:

Otto- The last formula in your post is what i was trying to write but using 30 instead of 29.93631. Another thing the cops' formula doesn't account for is weight. I would think that a corvette with equal length in skidmarks and on the same pavement as a 1-ton pickup with a loaded utility bed was going much faster than the pickup. The cops' formula would tell them they were going the same speed.

salmon_tacos · Posted: Mar 27, 2003 1:40 pm Post subject:

Wes,

The only reasons there would be a difference would be if you were accounting for downforce (Corvette probably has more) or if you were accounting for the fact that the Corvette almost certainly would have stickier tires than the truck.

If, however, those things were equal, then the skidmarks would indeed be the same...

Truck: More weight to stop but more weight on the tires
Corvette: Less weight to stop but also less weight on the tires.

Imagine if there is no weight on the tires. It would never stop no matter what the mass of the vehicle to stop is...it would just keep skidding and skidding.

Conversely, imagine if there were some external force (which does not contribute to the mass that needs to be decelerated) pushing down hard on the car. It could stop much faster (assuming it's brakes were up to the job).

porter · Outlaw Joined: 23 Jan 2003 Posts: 109 City: Sammamish

Strange, I thought I was on the boat discussion board. You guys must be really bored.

I dropped my car off the empire state building and it went from 0 to 60 in 1.5 seconds.

ohsix · Posted: Mar 27, 2003 3:26 pm Post subject:

salmon tacos- i understand what you're saying by the amount of weight on the tires but the kinetic energy of a 10,000 lb truck traveling at 40 mph is so much greater than a 3,000 lb corvette traveling at 40 mph. I know the added weight of the truck would cause more friction but i'm guessing it wouldn't be near enough to compensate for the added weight.

An example of this involving water and hull friction instead of rubber and asphalt would be a wakeboard boat traveling at 25 mph versus an oil-tanker traveling at 25 mph. even though the tanker has a lot deeper draft and more hull surface area in the water it will take it forever to get stopped compared to the light wakeboard boat because of the kinetic energy. The force of the water stopping them should be the same since each displaces the same ratio of water to weight.

salmon_tacos · Posted: Mar 27, 2003 4:47 pm Post subject:

Wes,

In both the friction and the energy equations, the mass has the same exponent, i.e. 1.

So, for example, if you double the mass of the vehicle, the energy will double but so will the friction.

Maybe you're thinking of the velocity which has 2 for an exponent? That's why a car going 60 takes more than just double the amount of time to stop than a car going 30.

I don't really know anything about hydrodynamics so I can't give you an explanation for your boat example. I only know there is more than just friction involved in stopping the boats (well...there is in cars too but it's sort of negligible).

ohsix · Posted: Mar 27, 2003 8:27 pm Post subject:

salmon- i think you meant acceleration instead of velocity.

stopping a vehicle is a force of acceleration. negative acceleration but still acceleration which has an exponent of 2.

salmon_tacos · Posted: Mar 27, 2003 10:01 pm Post subject:

No, I meant velocity, as in:

Kinetic Energy = (1/2)*(mass)*(velocity)^2

According to this equation, an increase in mass only increases kinetic energy linearly just like it does with friction. An increase in velocity, however, increases kinetic energy exponentially.

This was in response to your argument that the truck would create similar skid marks at a slower speed because it has so much more kinetic energy than the Corvette at the same speed. It is true that it has more kinetic energy but only insomuch as it also has more friction.

ohsix · Posted: Mar 27, 2003 10:42 pm Post subject:

if the corvette and the truck are on flat ground and both are traveling at 40 mph and you cut the power, neglecting wind resistance which would take longer to stop?

DRAGON88 · Posted: Mar 27, 2003 10:51 pm Post subject:

soo very confused.....i think im haveing an Aubs moment....lol

OttoNP · Addict Joined: 13 Jan 2003 Posts: 848 City: MI

Salmon_taco is right on, when you determine the stopping distance you figure out how much energy the vehicle has and then you determine how much work is needed to stop it. The energy is just the kinetic energy and the work is the force times the stopping distance, see below, M is mass, V is velocity, F is friction coefficient, N is normal force, G is gravity, and D is stopping distance:

KE=.5*M*V^2
Max Friction force =F*N =F*M*G (N is just the weight)
Work from friction force=F*M*G*D

Then you set these equal, .5*M*V^2=F*M*G*D, as you can see the M cancels

Wes,

The boat analogy is a good one except that a boat in water is much different than a car. Think about trying to push a boat around slowly, a person can move it around the dock pretty easy, now think about a car, it is harder to get a car moving. Yet, at the same time, a boat slows down much quicker than a car once you cut the throttle at higher speeds...think about it for awhile and if no one knows I'll post why...
For you question about the truck and the car, if you eliminate air resistance and have no braking, the only friction that will slow them down is rolling friction, which I'm thinking probably doesn't depend on weight as much as braking so I would guess the corvette would stop faster since your applying about the same force to both and it weighs less.

Nick
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OttoNP · Addict Joined: 13 Jan 2003 Posts: 848 City: MI

Salmon_taco is right on, when you determine the stopping distance you figure out how much energy the vehicle has and then you determine how much work is needed to stop it. The energy is just the kinetic energy and the work is the force times the stopping distance, see below, M is mass, V is velocity, F is friction coefficient, N is normal force, G is gravity, and D is stopping distance:

KE=.5*M*V^2
Max Friction force =F*N =F*M*G (N is just the weight)
Work from friction force=F*M*G*D

Then you set these equal, .5*M*V^2=F*M*G*D, as you can see the M cancels

Wes,

The boat analogy is a good one except that a boat in water is much different than a car. Think about trying to push a boat around slowly, a person can move it around the dock pretty easy, now think about a car, it is harder to get a car moving. Yet, at the same time, a boat slows down much quicker than a car once you cut the throttle at higher speeds...think about it for awhile and if no one knows I'll post why...
For you question about the truck and the car, if you eliminate air resistance and have no braking, the only friction that will slow them down is rolling friction, which I'm thinking probably doesn't depend on weight as much as braking so I would guess the corvette would stop faster since your applying about the same force to both and it has less mass.

Nick
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ohsix · Posted: Mar 28, 2003 7:59 am Post subject:

salmon_tacos · Posted: Mar 28, 2003 9:12 am Post subject:

Hey Wes,

If you took out wind resistance and braking, I think the truck would take longer to stop.

The reason I say this is that I believe the rolling resistance would be more similar between the vehicles than the mass. The surfaces are the same. I don't think the friction from the wheel bearings with matter much. The tires should be properly inflated on both vehicles so they should be of similar "roundness".

Actually, the Corvette, being set up for handling, probably has more toe and camber than the truck which would add to it's rolling resistance. So the Corvette, while having less mass and therefore less energy, might even have higher rolling resistence.

About the boat: I don't think it has anything to do with solid surface vs. liquid surface exactly. I would say it has more to do with the fact that the friction (drag) between the hull and water increases with speed. So, when you are pushing the boat around really slowly, there is very little resistance (less than the rolling resistance of a car). The energy it takes to move the boat a little is just whatever it takes to move a bit of water around from in front of the boat, which isn't very much when you consider that you are mostly just moving it around horizontally with very little friction.

salmon_tacos · Posted: Mar 28, 2003 9:13 am Post subject:

This is fun...I love arguing about random trivial stuff (well...trivial to a software developer anyway).

OttoNP · Addict Joined: 13 Jan 2003 Posts: 848 City: MI

That equation is just for the type of friction in sliding, rolling friction is different and that equation doesn't apply. A car mainly faces 2 forms of friction, rolling and air resistance. The rolling friction is larger at low speeds but friction from air resistance is larger at higher speeds. The friction from air resistance is based solely on the shape and the speed.

Air resistance is closer to the type of friction force a boat experiances from the water, as the boat speeds up the friction forces increase.

You can figure out a ton of things if you time how long it takes your car or boat to slow down from say 70-60 MPH or 65-60, etc...
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ohsix · Posted: Mar 28, 2003 10:33 am Post subject:

salmon- i meant all comnditions are the same on the two vehicles except mass. anyway, it looks like we all agree that the truck will travel further than the vette with rolling friction. what is the equation for rolling friction?

i understand what you are saying about pushing the boat but i still think a lot of it has to do with the different types of surfaces. if you simply get in the water and try to move the boat by swimming and pushing against it it's not going to move very easy.