BlackDog

Here's a good article -

HOW TO GET MAXIMUM ACCELERATION by Mike Clements

http://mclements.net/mrc-PowerTorque.html

PUR_SSYN

You speak as if the "wheel" is some sort of perpetual device and spins without
use of force?

What do you think is spinning the wheel? Itself? You need power to spin the
wheel. The motor spinning the wheel requires a certain amount of power to
sustain the motion.

Your analogy between the engine and wheel is not valid.

Alvin@pcmforless.com

Power is just work over time. How much work per time.

also

power = torque * angular speed (in rad/sec)

MyShibbyZ28

Read again.
My "spins around the crankshaft" was a very broad statement. Yes I know there needs to be energy, did I ever say there didn't need to be?

An engine spins around the crankshaft. What is spinning the crankshaft is the power coming from the cylinders. If the cylinders were not limited by factors such as air intake and gas, they could essentially have enough power and speed to make the crank spin as fast as you want. There are a ton of little limiting factors too. (ie valvetrain, drivetrain, strengths, friction)

Now a wheel is the same thing, except it doesn't necessarily have to be powered by cylinders. Anything can power a wheel. There can also be limiting factors like friction, strengths, and whatever depending on the powerer and enviroment.

Now how is my analogy not correct? A wheel and an engine both have to receive power to move, both have to give off that same amount of power received, and both need to receive constant power to stay moving. After all, what is that big thing behind the engine, I think it's called a flywheel.

)2overt SS

I didn't read all the posts... so, sorry if someone said this already, but

Horsepower = Power

Power = Work/Time

Torque = Work

Now think of it like this:

Seneario 1
Lets say 1 crankshaft rotation takes 1 second at 3,000 RPM (I know that makes no sense in reality.. but just bare with me)

Senario 2
Now lets say, at 6,000 RPM, 1 crankshaft rotation takes 0.5 seconds (makes sense, right? Because the engine is spinning faster so the time it takes to make one rotation will be less)

And lets also assume that at BOTH 3,000 and 6,000 RPM the engine produces 300 ft-lbs of torque.

Ok... now remember, Horsepower = Power and

Power = Work/Time

Work = 300 ft-lbs for both senarios

Senario 1

Horsepower = 300ft-lbs/1second = 300HP

Senario 2

Horsepower = 300ft-lbs/0.5seconds = 600HP

So to summarize as best I can

If the same amount of Work(Torque) is being produced all across the RPM range, the higher the RPM's the less time it takes for the engine to produce the same amount work(torque) so by

Horsepower = Torque/Time If Torque remains constant, as time decreases, horsepower will increase.

Hope that makes sense

Alvin@pcmforless.com

Thats a pretty good explaination.

Its really simple if you look at the formula

power = torque * omega (angular speed, can be replaced with RPM)

If torque is constant and RPM is faster than you are using more power

Alvin@pcmforless.com

A flywheel needs no net power nor does it need any net torque to stay moving.

remeber newton? A body in motion stays in motion unless acted on.


to make things clear here are the units.. They help me understand things

work/energy/torque= N-m also known as a joule
power = joule/s also known as watt


in english units

work/energy/torque = ft-lbf
power = 550ftlbs/sec also known as a HP

WS6T3RROR

an engine and trans most definaitly has momentum (more than one kind even in a moving car!), you get to feel the effects of it every time you upshift, that short sudden boost of acceleration when you hit the next gear is the rotating parts giving back energy to the system.

it doesnt have power it has angular momentum(energy), power to me would suggest some sort of force output, and a disc afaik falls very short in its design at getting anywhere near being something that can produce power, all of them i've seen have been pretty good at storing energy though (flywheels etc)

say wha

i'm still not sure i understand where you're going with that, wrt to the conversation. but at a glance i think we agree on the energy (word) equations there.

maybe i misunderstood when you started talking about spinning the disc faster and it being easier the higher its angular velocity was. that was the whole point of my momentum example.

Injuneer

The spinning wheel analogy loses me completely, and I'm still trying to find a definition of "protrude" that has anything to do with energy . The spinning wheel would continue to spin without additional power input, if you could just get rid of that pesky friction. It is not "protruding" (?) any energy, except to overcome fricton. The spinning wheel is all about inertia. I don't see the relevance to the question.

OldSStroker

Guys, terminology is very important. Don't confuse power, work, torque, momentum, etc. Those words and definitions are being used very loosely in this thread. The terms are NOT interchangable!

No offense pHEnomIC, but I'm not convinced that you do understand torque and hp. Torque, as produced by an rotating engine is work. Work over a time period is power, as Alvin said.

Example of work and power:

You weight 165 lbs. and walk up a flight of stairs that is 10 feet high. You did (165 lbs. x 10 ft) or 1650 lb-ft of work. If you took your time and did it in 60 seconds, you produced 1650/60 or 27.5 lb-ft/sec of power. Because one horsepower is defined as 550 lb-ft per second, you produced 27.5/550 or .05 hp. That's 1/20 of a hp.

If you climbed the stairs in 6 seconds you would have produced 1650/6=275 lb-ft/sec or 1/2 hp. If you ran up the stairs in 3 seconds, you produced.....I'll leave the math to you. In each case the work was the same, only the time, and therefore the power varied.

HP can be thought of as how fast you produce torque. That's in the formula: HP = torque x rpm/5250. So the higher the rpm you can make torque, the more power you are producing. 300 lb-ft @ 3000 rpm is 171.36 hp, but 300 lb-ft @ 6000 rpm is 342.72 hp. That's why a 183 cubic inch F1 engine can produce 900 hp @ 18,000 rpm. It's only getting 262.6 lb-ft at that rpm, by the way.

So if the F1 engine is only producing 262.6 lb-ft at its 18,000 rpm power peak, how could it accelerate a car quicker than an engine making 300 lb-ft at say 6000 rpm power peak? This opens a whole new container of worms, doesn't it?

PUR_SSYN

MyShibbyZ28,

I've read your replies more than once in hopes that I had miscontrued your
intentions.

At this point, you need to take this debate back to your grade school physics
teacher and try to explain your position. Everyone in this thread is quoting
you for a reason. Please try to take their advice and learn from them.

WS6T3RROR

you just couldnt resist could you.

given the same tire height and vehichle mass and perfect traction the f1 car can use 3x the gearing as the 6000rpm street car.

f1 262.6 x 3 = 787.8 lb-ft
street car 300 x 1 = 300 lb-ft

using force = mass (accel) and ignoring force and mass since they're equivalent. the f1 car should accelerate at a rate 2.626 times that of the 6000rpm engine.

note: if you could get the street car to duplicate the tq output of the f1 engine the bhp would be the same at the axle.

I left out tire radius, thrust, and effective gearing on purpose to avoid even more confusion, and to simplify the example.

rskrause

Pretty much addresses what I was trying to get people to think about if you carry it one step further and answer the last question. And believe me, with the right gearing that F1 motor WILL make a vehicle accelerate faster than the "lazy" 300ft.lb. @ 6,000rpm motor. So, isn't it ridiculous when people say "hp doesn't matter, it's just torque that matters?" They are directly related (HP = torque*rpm/5250) so if one matters, so does the other.

Rich

Alvin@pcmforless.com

Pot meet kettle..


Your post are full of mistakes and wrongs also.

Power and force are two seperate things. It takes force to accelerate a wheel spinning or counter friction in your real world senerio, there is no net power needed to sustain a spinning wheel nor is there any net force require to sustain a wheel spinning.

PUR_SSYN

There is if it's attached to a car with aero drag and
moving several miles per hour.

Correct me if I'm wrong, but isn't that what we're discussing? Engine torque
and horsepower?