I’ve heard this nutty claim circulating for years, so it deserves to be put to bed–or proven.
A friend once claimed that he got a ride in a buddy’s souped-up street car that was so fast that the owner took a $20 bill out of his wallet, placed it on the dashboard, and said: “I’m going to floor it. If you can reach up and grab the money, it’s yours.” My friend claims that the acceleration was so wicked he actually couldn’t lift his arm to grab the bill.
This seems nutty. If we ignore the problem of the bill staying in place, how many G’s would a car have to generate to prevent your average guy from reaching up and grabbing the money? I can’t imagine even a fuel funny car generating enough G’s to do that.
Since this ain’t exactly IMHO, what are your (science-based) thoughts?
By the way, am I imagining it, or are the “muscle cars” of today actually faster accelerating than those of the 60s? The auto makers seem to have really gotten good at maximizing the torque in small, turbocharged engines.
Well, I don’t usually attempt math when I’ve had a couple of drinks, but WTH. Let’s say we’re talking 0-60 mph in 5.0 seconds (that would be one of your higher end muscle cars). It seems to the slightly soggy beatle that your average acceleration (a) would be
a = delta v/delta t
delta v being the change in velocity and delta t being the change in time. This gives me an a of 17.6 ft s[sup]-2[/sup], or slightly less than 2G.
Practically speaking, I grew up during the golden age of muscle cars, and I wish I’d known the guy who laid 20s on the dash (would not have been too tough to grab the Jackson - think about it, how’d they shift gears?).
Of course, I’m unfamiliar with the specific rocket-sled to which your bud refers.
One “g” of acceleration is 9.8 m/sec per sec, or roughly a 0-60 mph time of 3 seconds. Since that acceleration acts tangent to gravity, your arm would weigh 1.4 times its normal weight, with the combined forces directed down and back.
Two "g"s of acceleration would multiply your arm’s normal weight by a factor of sqrt(2[sup]2[/sup]+1[sup]2[/sup]), or 2.23
Three "g"s is a factor of 3.16. For the sake of simplicity, let’s say this is where it starts to become difficult to lift your arm… a 26 pound additional load onto a 12 pound arm.
A three G acceleration would require a net force of over five tons to accelerate a 4000 pound vehicle at 3g- that’s a 0-60 time of approximately one second. That would require 960 horsepower at low PRM, and assumes no losses to rolling friction and aerodynamic drag.
Sounds pretty unlikely for a street-legal, gas-powered vehicle.
Yeah, I screwed up my units there (metric garvitational acceleration mixed in with feet). Slightly soggy beatle will still defend the practical observation and get back to the math in a bit.
Which is not ~2G as it’s all in feet (with g=32’[sup]-2[/sup])
I suppose I’m working this problem wrong, but you could still snag the 20. It’s interesting to see KeithT’s entirely different approach to it.
If I’ve not failed my arithmetic (entirely possible), perhaps the question involves the vectors. While standing on earth your usual experience of G normal to that of earth’s gravitation is near zero and the G force I’ve discerned for the passenger in an L-88 'vette is only slightly more than .5 G, but .5 G above what he/she usually experiences.
So, is the water muddy enough yet, or should I go on?
According to one site, a '69 GTO weighs 3503lbs and has 370hp. According to Yammaha, a '98 YZF-R1 weighs 390lbs and has 150hp. Taking these numbers as accurate*, the YZF has 2.74 times the power to weight ratio, hence 2.74x the acceleration.
If no one could touch the windshield of a muscle car when it’s running, then no one could give a YZF full throttle without getting pulled off the back …right?
(Geez, I thought I swore off the SDMB…)
*[sub]Yes, the SAE went to rear wheel measurements in '72 and manufacturers may sometimes fudge their performance specs …and I’m quoting peak HP (which should apply) and adding a 150lb driver. Hey, It’s a seat of the pants figure.[/sub]
**
If no one could touch the windshield of a muscle car when it’s running, then no one could give a YZF full throttle without getting pulled off the back …right?
**
Right. I thought so, too, but I wanted you guys to work on it. If the acceleration were that powerful, you couldn’t operate the car at all–your feet and hands would be pulled from the pedals/steering wheel.
**Anyone with thoughts about the new muscle cars compared with those of the 60s and early 70s? **
There’s a difference between reaching forward to the dashboard and keeping your hands on the steering wheel once you’ve already got a grip on it. The difference between doing a pull up and bench pressing your body weight.
I’ve heard this story, too. When I heard it, it was about a Cobra and a fifty-dollar bill clipped to the sun visor (which makes sense, if it was just on the dashboard the acceleration would make it fall back into my lap). I always think back to one time I went flying with my dad. I was sitting in the back seat while he was practicing 60-degree banked turns (which pull 2 G’s, directed straight down relative to the aircraft) and I tried to reach up to adjust the fresh air vent in the ceiling. I was too young to anticipate the effect of the G’s, and I still remember how strange it felt to put so much extra effort into raising my arm. But I was able to reach the vent.
There might still be some truth to the story. With the G force acting at an odd angle, the fluctuations when the car shifts gears, and the fact you’d only have a few seconds to grab the bill anyway, it might have happened. But I wouldn’t try it with my own fifty.
My older step-brother told me he used to do this in his car, with a slight variation. He’d put the $20 on the floor in front of the passenger’s feet. The bet was to get it before they reached 60 MPH. So this would entail the extra effort of leaning forward and down to the money. He claimed that just as someone would get close to reaching it, he’d shift to 2nd which would throw them back again. The car was a Dodge Dart with a heavily modified 340 engine and huge rear tires. With idea conditions, it would lift the front wheels off the ground when launching.
My dad had a '65 Impalla SS big block, and when I was all of about 90 pounds, he would stomp it and glue me to the seat. If I had to touch the windshield or the top of the dash, it’d be very hard.
The seats were slippery, the dash was far away, realtive to modern cars, and the torque came on fast.
You don’t really need to consider muscle cars of the 60’s because many modern cars run with or ruin faster. It only took us almost all of the 70’s 80’s and some of the 90’s to get back to that kind of acceration, but it was worth the wait.
!!!Real World results are in:)
(Tested this with the wife (135lbs, 5’7") in my 1995 Mustang Cobra 5spd, 320+ HP and 330+ lb/feet torque, 0-60 near 5 secs: Results: she is 20 bucks richer. Also tested in 2001 Dodge Dakota 4.7 V8 w/ 235 HP and 300 lb/ft of torque and dash farther away: She did it again!)
Sounds like legend to me, but I’m sure it’d be hard for a kid in an old muscle car, as I recall.
This sounds like a varient of what Caroll Shelby used to do in the Shelby Cobra and later in the Dodge Viper. I believe he is the origin of this tale, be it actual or UL.
*The AC Cobra is renowned for its acceleration and it is said that during cars launch this was demonstrated to potential buyers by placing a $100 dollar bill on the dashboard in front of the passengers seat. The buyer could keep the $100 dollar bill if they could reach it as the car accelerated. Apparently no one ever did. *
Okay, that’s for the AC Cobra, not the Shelby. But this has Caroll’s style written all over it. I’ll get to checking.
some of the legends associated with Shelby’s cars:
The 0-100-0 thing.
A Hertz rental GT-350 winning SCCA races on weekends in California (it seems true that some were definitely raced, though).
The dashboard thing.
All kinds of weird stuff involving Caroll Shelby, George Lucas, Robert Duvall and the GT40.
The maximum acceleration a car’s wheels can provide, in Gs, is the coefficient of friction between the tires and the road, BTW. So far as I know, there’s no known rubber with a coefficient of friction with asphalt higher than 2, and most are less than 1, so that would put a ceiling on the acceleration of 1 or 2 Gs. Any moderately fit person ought to be able to lift their arms against that.
Ok, some important points everybody is missing (unless I misread the thread):
Sofa King–The AC Cobra is the Shelby Cobra. The Cobra is Carroll Shelby’s modification of the AC Bristol Roadster, with a Ford 302 or 427 (either one is overkill for that little frame), hopped-up suspension, flared fenders, roll bar, etc.
Re bill on dashboard-- The trick here isn’t that the car produces so much acceleration that you are physically unable to lift your arm. That’s silly. You could lift your arm (albeit with much effort) even under 3g of lateral acceleration (as Keith T pointed out), and no car short of a top fuel dragster or a funny car can accelerate anywhere near that fast (1g=32ft/s[sup]2[/sup]. 0-60 in 3 sec, pretending we have constant acceleration, is only 29.3ft/s[sup]2[/sup]). The trick is that it’s really hard to make precise, controlled movements (catching a dollar bill) under conditions where the apparent weight of your arm is changing rapidly and irregularly.
As the car accelerates, several things happen:
[list=1]
[li]The bill starts to slide backwards. This can make it more difficult to catch even under ideal circumstances.[/li][li]The weight of your arm is increased by varying amounts. Think back to when you were an infant, first learning to use your arms and legs. Remember? Of course not. But the point is that we have all learned to make controlled movements under a very specific set of conditions: Gravity is constant. Your arm doesn’t suddenly get heavier. So your movement to try and catch the bill is awkward and uncontrolled.[/li][li]The gravity vector is no longer vertical. Again, a minor thing, but enough that your fine motor skills will feel off-kilter.[/li][li]You have only a second or so to catch the money before it hits the seat (part of the bet, right?). So even though you could overcome all the previous effects, you have very little time to make corrections to your movements.[/li][li]If the driver wants to cheat, he/she can choose to stomp or let up on the gas pedal to make your task even more difficult.[/li][/list=1] Chronos–I don’t know the frictional coefficients of tires, but I know this: Top Fuelers produce acceleration significantly higher than 3g. This past weekend in Gainesville Fl, a driver made a 1/4 mile run in 4.591 seconds at 326.79mph. That’s an average acceleration of 104.4 ft/s[sup]2[/sup], or about 3.26g. Of course it’s not smooth acceleration, so parts of it were less than that, but that means that bursts had to be even higher to average 3.26.
Okay, muscle car fans. Last Saturday, Marcie and I were in Naples, Florida. We went out for a Bagel Breakfast and while we were sitting outside in the sunshine, a Cobra with the 427 engine pulled into the parking lot. The guy driving the thing got out and went into the bagel shop, giving me the opportunity to scope the thing. Pure beauty and the engine sound was unforgetable—better than a Harley, and that is better than sex. The custom Florida license plate was “King Cobra.” Did I see Shelby himself? Or at least his car?
I da man!