just trying to understand
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just trying to understand
just been brushing up on things i forgot/didn't know on howstuffworks.com, and i was reading all the definitions on power, torque, energy, and work. from the beginning and up to now, i still would have trouble answering somebody if they asked me, "what's the difference between horsepower and torque?" torque is no problem, but i would have trouble with defining horsepower. so basically let me give my version of a definition of hp that i have gathered from the site and you guys can correct me if i'm wrong or add on stuff.
Torque is a force that turns/rotates things (mooched from site) and the SI unit is the Newton-meter.
Power is a measure of how quickly work can be done (mooched again) and the SI unit for power is the watt.
One watt is equal to 1 Newton-meter per second (Nm/s).
since the si unit for torque is the Nm, this shows that power is related to torque. also, since the watt is related to horsepower---> 1 horsepower equals 746 watts--->horsepower as defined by me is a measurement of the amount of torque that can be done in a certain period of time.
sorry for the intro and **** but i had to create a basis to try and make my definition logical (or seem to be if it's wrong) any help appreciated [IMG]i/expressions/beer_yum.gif[/IMG]
Torque is a force that turns/rotates things (mooched from site) and the SI unit is the Newton-meter.
Power is a measure of how quickly work can be done (mooched again) and the SI unit for power is the watt.
One watt is equal to 1 Newton-meter per second (Nm/s).
since the si unit for torque is the Nm, this shows that power is related to torque. also, since the watt is related to horsepower---> 1 horsepower equals 746 watts--->horsepower as defined by me is a measurement of the amount of torque that can be done in a certain period of time.
sorry for the intro and **** but i had to create a basis to try and make my definition logical (or seem to be if it's wrong) any help appreciated [IMG]i/expressions/beer_yum.gif[/IMG]
[IMG]i/expressions/face-icon-small-smile.gif[/IMG][IMG]i/expressions/face-icon-small-smile.gif[/IMG][IMG]i/expressions/face-icon-small-smile.gif[/IMG] w00t! 
Science + Math = Best subjects [IMG]i/expressions/face-icon-small-smile.gif[/IMG][IMG]i/expressions/face-icon-small-smile.gif[/IMG][IMG]i/expressions/face-icon-small-smile.gif[/IMG]
Science + Math = Best subjects [IMG]i/expressions/face-icon-small-smile.gif[/IMG][IMG]i/expressions/face-icon-small-smile.gif[/IMG][IMG]i/expressions/face-icon-small-smile.gif[/IMG] 
DIY King
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Rep Power: 419 Torque is what you're looking for when you look at a dyno since it changes with the rpm. Horsepower is just the torque at one rpm. I think this is a standard, but I forget what rpm that is? [IMG]i/expressions/face-icon-small-confused.gif[/IMG] Anyway, look at where the torque line and horsepower line cross on a dyno chart. That's where the horsepower measurement is taken.
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[hr]Originally posted by: RyzRocket02
They are both used to measure power. Torque just measures rotational power while horsepower measures pulling power. That's the simpliest explanation I can come up with.[hr]
[hr]Originally posted by: RyzRocket02
They are both used to measure power. Torque just measures rotational power while horsepower measures pulling power. That's the simpliest explanation I can come up with.[hr]
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[hr]Originally posted by: Grey
Torque is what you're looking for when you look at a dyno since it changes with the rpm. Horsepower is just the torque at one rpm. I think this is a standard, but I forget what rpm that is? [IMG]i/expressions/face-icon-small-confused.gif[/IMG] Anyway, look at where the torque line and horsepower line cross on a dyno chart. That's where the horsepower measurement is taken.[hr]
[hr]Originally posted by: Grey
Torque is what you're looking for when you look at a dyno since it changes with the rpm. Horsepower is just the torque at one rpm. I think this is a standard, but I forget what rpm that is? [IMG]i/expressions/face-icon-small-confused.gif[/IMG] Anyway, look at where the torque line and horsepower line cross on a dyno chart. That's where the horsepower measurement is taken.[hr]
edit: cool link of hp, torque, and power to weight ratio of several sports cars
i just found this on howstuffworks.com, pretty sweet
DIY King
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Rep Power: 419 I'm not sure why the crossing points would be different? They should be at 5,252rpm. I guess the dynonometer isn't that accurate then? [IMG]i/expressions/face-icon-small-confused.gif[/IMG] This is a good link: How Horsepower Works Basically your link, but a different page...
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Rep Power: 0 Quick version:
HP = Torque X RPM / 5252
where torque is in FT-LBS (not newton-meters or any other force-length)
This equation will give you the horsepower at any RPM, provided you know the torque (given to you by the dyno).
Long version:
(taken from a cached page, <pages.prodigy.net/csw_cmt/page8.htm>[IMG]i/expressions/face-icon-small-wink.gif[/IMG]
The truth is, if an engine makes power, it will show up on a dynamometer. Dynamometers (dynos) measure power output from engines. They do this by measuring the torque, or twisting force in foot / lbs. at a convenient output shaft (crank shaft or transmission output shaft / countershaft) or rear wheel. The torque is determined through the use of a hydraulic or water brake, eddy current power absorption unit or inertia drum. All of these units force the engine to perform work against a known load. The term brake horsepower comes from premise that a brake affixed to the shaft of an engine could be gradually applied until the rpm is held constant. The brake, if attached to a fixed and floating rod system like old style torque wrenches, will deflect slightly (this was called the prony brake). Through the deflection of the brake arm, torque in foot lbs. can now be read. New brake style dynos use a much higher tech method of measuring the deflection with electro- mechanical sensors. The software compares the engine rpm to torque and calculates the horsepower from these figures. The formula is rather simple but it's roots complex.
Horsepower = (Torque x RPM)/5252
Where torque is measured in foot / lbs. Rpm is the rpm where the particular torque figure is obtained. 5252 is a constant. This is a standard.
If you notice, when the rpm is equal to 5252 the torque will equal the horsepower. This is always the case, it never changes. Every dyno chart will show the torque and horsepower as being equal at 5252 rpm. If you see a chart that does not look like this, it's a fraud. Don't buy an engine from this person. In fact, I wouldn't recommend buying a used car, motorcycle or cup of coffee from this guy. The numbers are based on simple physics and physics never breaks.
The constant 5252 goes back all the way to the 17th century. A man named James Watt developed a steam engine to pump water out of coalmines. There was no convenient measurement standard so Watt had to equate his engine to the power of the previous standard, the draft horse. The typical arrangement was a draft horse pulling on a 12-ft. lever affixed to a turnstile (the pump was driven by the turnstile). The pulling force of the horse was estimated to be 180 pounds. The circumference of the twenty four-foot turnstile circle is 75.4 feet. (2 x pi x 12 ft. = 75.398 ft.) A good horse could make 144 revolutions per hour which equals 2.4 revolutions per minute. 2.4 x 75.4 ft. = 180.96 ft. which was rounded up to 181 ft. / min.
Watt took the 180 lbs. of force and multiplied it by the 181 feet to get 32,580 lbs.- feet of force per minute. If 32,580 lb.-ft. of force is rounded up to 33,000 and divided by 60 sec. we get 550 lbs.-feet per sec. Thus 550 lbs.-feet per sec was determined to be the average power output of the draft horse.
How does this relate to the modern engine? James Watt had to equate this to his steam engine, which had a crankshaft like a modern engine, to the horse. His engine turned the center of the aforementioned turnstile, not the 12-foot lever. To finish the equation he "affixed " a lever off the crankshaft. For ease of calculation he used one foot as the length. The length of travel of the one-foot lever is:
2 x pi x one ft = 6.283 ft
To relate this to the average horse calculation, the total distance the end of the lever travels in one minute would be 6.283 ft. x rpm. When this figure is multiplied by the torque output of the engine we get the total lbs.-feet of torque per minute. If we divide this by 33,000 (Watt’s figure for lbs.-feet per minute for one horsepower) we will get the horsepower for the given engine. To recap:
Horsepower = (6.283 x RPM x torque)/33,000
Simplified we get:
Horsepower = RPM x torque
5252.268
The numbers are still a little too cumbersome so we round 5252.268 to 5252. Hence the simple equation referred to at the opening.
HP = Torque x RPM / 5252
Hope this helps,
Joey
HP = Torque X RPM / 5252
where torque is in FT-LBS (not newton-meters or any other force-length)
This equation will give you the horsepower at any RPM, provided you know the torque (given to you by the dyno).
Long version:
(taken from a cached page, <pages.prodigy.net/csw_cmt/page8.htm>[IMG]i/expressions/face-icon-small-wink.gif[/IMG]
The truth is, if an engine makes power, it will show up on a dynamometer. Dynamometers (dynos) measure power output from engines. They do this by measuring the torque, or twisting force in foot / lbs. at a convenient output shaft (crank shaft or transmission output shaft / countershaft) or rear wheel. The torque is determined through the use of a hydraulic or water brake, eddy current power absorption unit or inertia drum. All of these units force the engine to perform work against a known load. The term brake horsepower comes from premise that a brake affixed to the shaft of an engine could be gradually applied until the rpm is held constant. The brake, if attached to a fixed and floating rod system like old style torque wrenches, will deflect slightly (this was called the prony brake). Through the deflection of the brake arm, torque in foot lbs. can now be read. New brake style dynos use a much higher tech method of measuring the deflection with electro- mechanical sensors. The software compares the engine rpm to torque and calculates the horsepower from these figures. The formula is rather simple but it's roots complex.
Horsepower = (Torque x RPM)/5252
Where torque is measured in foot / lbs. Rpm is the rpm where the particular torque figure is obtained. 5252 is a constant. This is a standard.
If you notice, when the rpm is equal to 5252 the torque will equal the horsepower. This is always the case, it never changes. Every dyno chart will show the torque and horsepower as being equal at 5252 rpm. If you see a chart that does not look like this, it's a fraud. Don't buy an engine from this person. In fact, I wouldn't recommend buying a used car, motorcycle or cup of coffee from this guy. The numbers are based on simple physics and physics never breaks.
The constant 5252 goes back all the way to the 17th century. A man named James Watt developed a steam engine to pump water out of coalmines. There was no convenient measurement standard so Watt had to equate his engine to the power of the previous standard, the draft horse. The typical arrangement was a draft horse pulling on a 12-ft. lever affixed to a turnstile (the pump was driven by the turnstile). The pulling force of the horse was estimated to be 180 pounds. The circumference of the twenty four-foot turnstile circle is 75.4 feet. (2 x pi x 12 ft. = 75.398 ft.) A good horse could make 144 revolutions per hour which equals 2.4 revolutions per minute. 2.4 x 75.4 ft. = 180.96 ft. which was rounded up to 181 ft. / min.
Watt took the 180 lbs. of force and multiplied it by the 181 feet to get 32,580 lbs.- feet of force per minute. If 32,580 lb.-ft. of force is rounded up to 33,000 and divided by 60 sec. we get 550 lbs.-feet per sec. Thus 550 lbs.-feet per sec was determined to be the average power output of the draft horse.
How does this relate to the modern engine? James Watt had to equate this to his steam engine, which had a crankshaft like a modern engine, to the horse. His engine turned the center of the aforementioned turnstile, not the 12-foot lever. To finish the equation he "affixed " a lever off the crankshaft. For ease of calculation he used one foot as the length. The length of travel of the one-foot lever is:
2 x pi x one ft = 6.283 ft
To relate this to the average horse calculation, the total distance the end of the lever travels in one minute would be 6.283 ft. x rpm. When this figure is multiplied by the torque output of the engine we get the total lbs.-feet of torque per minute. If we divide this by 33,000 (Watt’s figure for lbs.-feet per minute for one horsepower) we will get the horsepower for the given engine. To recap:
Horsepower = (6.283 x RPM x torque)/33,000
Simplified we get:
Horsepower = RPM x torque
5252.268
The numbers are still a little too cumbersome so we round 5252.268 to 5252. Hence the simple equation referred to at the opening.
HP = Torque x RPM / 5252
Hope this helps,
Joey
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