I just went over it again..... my accuracy has slipped into lunacy.

Although I got the same answer for both ends of the equation, I should have divided on both sides instead of multiplying to do the minute to second conversion (I applied a linear time progression conversion instead of per second conversion).

360 lb-ft @ 6000 RPM
360 lb-ft @ 100 RPS

RPM Crossover = 5252

60 seconds in 1 minute, therefore:
(convert per-minute to per-second, not the linear time progression conversion that we attempted earlier)
1 second = 1/60 of a minute
RPS Crossover = RPM Crossover / 60

RPS Crossover = 5252 / 60
RPS Crossover = 87.533333333333333333333333333333

HP = ((TQ @ RPS) X RPS) / RPS Crossover

HP = (360 X 100) / 87.533333333333333333333333333333
HP = 411.27189642041127189642041127191

OK, now where are my cookies?

k = RPS Crossover
k = 87.533333333333333333333333333333

Although I did it backasswards previously, I am still right in that we converted the entire formula into seconds and you only did half of it which will lead to very wrong answers.

Yes... I've slipped and I'm nuts..... honey roasted....hmmm

 

YAY! Cookies for all!!

 

OK guys. VIP finally got it! Should I send over the Girl Scout.....cookies?

I think you were getting lost in the numbers and losing sight of the concepts...reality, as it were. That is what I was trying to point out earlier. If you understand the concept, you can "derive" the correct formula, and you will know whether you are correct or many orders of magnitude off. That actually counts in the real world.

What you called "RPS crossover" is just the constant (I like "K" or actually "J" if you are a "MIB" fan ) which makes the units (like lb-ft, and revs) work out correctly. Do you see why 5252 is easier to remember than 87.5352187...

Oh, to be precise, remember the "5252" constant is really 33000 lb-ft/ 2 π radians or 5252.113122.. We round it off because 5252 is only about .002% off. Close enough for engine power when we rarely go past 1 decimal place.

BTW, you actually get the 87.53...constant by dividing the 550 lb-ft/sec (not rounded, but the definition of hp) by 2 π.

"Revs" is the difficult unit to work into a formula. We can measure lb of force, feet and seconds (or minutes or years), but revs often cause a problem. That why the equivalence of 2 π radians = 1 rev helps out. You remember the definition of a radian, right?

In the real world you need to KNOW why the numbers are correct. If you understand the concepts, you will have a better chance of getting where you want to go.

The world (Mother Nature) doesn't run on math. Math is used to explain what happens; math doesn't cause it.

Mother Nature isn't a mathematician, She is a practicing physicist, and one tough ol' broad. I've had a crush on her for many decades.

End of lecture.


Jon

PS: Stay awake in physics classes, or Ma Nature will wrap you on the knuckles somewhere down the line. See my siggy quote from a great engineer named Tom.

 

Send girl scout WITH cookies.

 

"Should I send over the Girl Scout.....cookies?"

You aren't as slow as VIP said you were!

Another bonus question (you might pass this course yet):

Why did the DIN (European) specification use the term "ps" for horsepower before they went metric with Kw instead of horsepower? Why is ps still used?

 

oh oh can i answer this one?
Ps stands for a german word that roughly means horsepower Its calculated using a kilopond *m/s
Where english horsepower is used by lbf*ft/min. 1ps is about .986 hp

Isn't ps still used just because its harder for some people to grasp the new metric system using kW

 

More info on horsepower. Believe at your own risk.

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

 

VIP said I was slow?

 

Just pulling your leg. Note the

I never claimed to be a nice person, just a "knowitall" like my hero Cliff Clavin.

 

Is that Burt Reynolds in your avvy?

 

Yeah, Burt and I are often mistaken for brothers.

FWIW here's the connection:

1) Burt played the title role of Stroker Ace in the movie.

2) My son Bret posts (elsewhere) as SStrokerAce because 1) he drives a Camaro SS 2) he thinks the movie is a hoot or 3) he just likes Lonnie

3) I have an LT1 Impala SS, and am 35 years older than SStrokerAce, so I took the name Old SStroker. The avatar is an older Burt.

Man, I really look nothin' like Burt! The Popeye avatar was closer.


As for the siggy, Bo Darville (aka the Bandit) was also a character played by Burt. If you know Bret and his experiences here you will understand my last siggy quote. Yes, it is really from the movie.

Jon Bauer, the Old SStroker

 

I can follow the concepts, I just had a brain fart with the numbers.

I Know. I was just being more descriptive about what it is.


My call sign tends to end up being PITA.

Covered it in a Pre-Calculus class in high school years ago. Can't say I've though much about it since though. Had a teacher that gave us a big math project to do over Christmas Break that has a big portion of the year's grade. That was annoying.

Actually you often don't need the why or how as long as it works.

Physics is mostly math.... and calculus makes it so much faster/easier to calculate.



BTW, I liked Stocker Ace and I do get the reference in your sig.
I have it on DVD.


Nope... he was joking....which he already said...

 

Hey to bring up a old post in this thread...

Wouldn't the metric version of RPM still be RPM, revolutions per minute? We could substitute any acronym in there and it wouldn't matter because the threory is still the same: Degress rotated/time

 

Of course!

I guess the wasn't enough of a hint that I was trying to be facetious.

 

Don't ever say that, even in jest! People will think you mean it and that you personify one of Mark Twain's most famous quotes.

I'm just pis*ing into the wind here aren't I VIP?

Life's too short for that.

Later...

 

I get a mist every once in a while myself.

You're not losing me.... I just tripped over my own feet.

 

This is the coolest thing you have ever said. I love those cars. Is it maroon, black, or green?

 

Damn. You are easy to impress.

How about very early 1997 C5 with 115,000 miles as a year-round DD here in the north country? Vanity plate UNRED

SS has 120,000 miles, vanity plate is KLR WHL

There are very few maroon or green whales, and all Corvettes are not red.

FWIW: Son has black Camaro SS and black silverado, wife has black Audi and there is also a black S15 p'up.

Back OT (sorta). The translation for the German "ps" is loosely "Horse strength". Very descriptive, IMO. Yes, most folks don't relate KW to horsepower very well. I have trouble converting N-m of torque easily to lb-ft in my head, and Kw only sounds right for a Prius.

OK so why is a Ford Fusion not powered by a miniscule bit of hydrogen?

 

haha, hydrogen. BOOOOM!

my highschool friend has a green whale. headers true duals, tuned, intake, TB, and a sexy new leather interior.

I love it.

 

You should change your username to oldriddler....

Its because the only way we have achieved fusion is as a byproduct of a fission event. IE Thermonuke explosion. Wouldn't work well in the automotive world me thinks.