Physics: How does more rpm = more power
#16
Re: Physics: How does more rpm = more power
Here's a good article -
HOW TO GET MAXIMUM ACCELERATION by Mike Clements
http://mclements.net/mrc-PowerTorque.html
HOW TO GET MAXIMUM ACCELERATION by Mike Clements
http://mclements.net/mrc-PowerTorque.html
#17
Re: Physics: How does more rpm = more power
Originally Posted by MyShibbyZ28
How so? A wheel spins, so does an engine. Spins around the crankshaft.
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.
#19
Re: Physics: How does more rpm = more power
Originally Posted by 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.
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.
Originally Posted by MyShibbyZ28
It takes power to get it moving, but it also has to protrude that same power. So in a sense it has power. If a disc is spinning in space, you can obviously stop it if something is not driving it. But if something is driving it, you need to over come the power of the driver, since the power is being transfered. I guess that is really what I was getting at.
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.
Last edited by MyShibbyZ28; 01-03-2006 at 12:40 PM.
#20
Re: Physics: How does more rpm = more power
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
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
#21
Re: Physics: How does more rpm = more power
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
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
#22
Re: Physics: How does more rpm = more power
Originally Posted by MyShibbyZ28
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.
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
#23
Re: Physics: How does more rpm = more power
Originally Posted by MyShibbyZ28
Are you saying an engine doesn't have momentum?
Originally Posted by MyShibbyZ28
And also, how does a spinning wheel have no power?
Originally Posted by MyShibbyZ28
It takes power to get it moving, but it also has to protrude that same power. So in a sense it has power.
Originally Posted by MyShibbyZ28
If a disc is spinning in space, you can obviously stop it if something is not driving it. But if something is driving it, you need to over come the power of the driver, since the power is being transfered. I guess that is really what I was getting at.
Originally Posted by MyShibbyZ28
I wasn't really trying to get at all the acceleration stuff.
#24
Re: Physics: How does more rpm = more power
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.
#25
Re: Physics: How does more rpm = more power
Originally Posted by pHEnomIC
I know what torque and hp are by definition but what I am wondering is how does more rpm = more torque on most combustion engines. Does the faster burning of more gas stack up the power? It just puzzles me a little bit because i think of this analogy. Say there is a bolt that requires 100 ft/lbs of torque to bust it loose and your ratchet can only give 80 ft/lbs. No matter how much you power the ratchet for, it wont stack up to the 100 required.
I don't know if this makes sense but can you explain to me what goes on exactly and possibly even explain to me what i am thinking because Im not too sure it is correct either.
I don't know if this makes sense but can you explain to me what goes on exactly and possibly even explain to me what i am thinking because Im not too sure it is correct either.
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?
#26
Re: Physics: How does more rpm = more power
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.
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.
#27
Re: Physics: How does more rpm = more power
Originally Posted by OldSStroker
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?
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.
#28
Re: Physics: How does more rpm = more power
Originally Posted by 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?
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?
Rich
#29
Re: Physics: How does more rpm = more power
Originally Posted by 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.
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.
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.
#30
Re: Physics: How does more rpm = more power
there is no net power needed to sustain a spinning wheel nor is there any net force require to sustain a wheel spinning.
moving several miles per hour.
Correct me if I'm wrong, but isn't that what we're discussing? Engine torque
and horsepower?