I enjoyed this excellent review of the physics of power! Is there any way do the comparison between/among engines similar to that demonstrated in the article to allow more intelligent purchase of motor vehicles? Is this information readily available from the companies, or does Consusmer Reports or some such magazine provide this information/service? Thanks.
Presumably this is in reference to What’s the difference between horsepower and torque?, which doesn’t officially appear until next Tuesday.
Thank you very much for the kind words.
The truth is, I’m not certain exactly how easy it might be. My article was very simplified to fit into the alloted space for presentation reasons on the Reader’s server. However, I think in truth one would have to take into account a large number of factors. The big ones which an average comsumer would notice being:
- Price (cost as an option on the vehicle)
- Fuel economy
- Low, mid-range, and peak power
- Noise/vibration
Then there are things which a more automotive mind might consider:
- Reliability
- Ease/cost of maintenance
- Sound (that “V8 growl”)
- Responsiveness to throttle changes
A scientific mind might consider:
- Emissions of CO, HC, NOx, CO2, aldehydes
- Overall thermal efficiency
An economic mind might consider:
- Origin of the engine/parts (domestic vs. foreign)
- Levelized annual cost of operation
It’s certainly a task that can take a while to go through the options.
Disclaimer: I may be horribly wrong, as this information came from a public education system, and we all know how great those have been over the last twenty years.
As I say, I may be wrong, but I could swear up and down that I once read a textbook which said that the measure of horsepower was related to the amount of time that it took a horse to lift one pound off the ground. These measurements were then used to calculate how much energy the horse had used (ie how much work it had done), which was the measurement applied to horsepower. Now, the only evidence I have for this is anecdotal, but the text had a real nice old-fashioned-looking line drawing of Watt watching a horse lift a weight by means of a pulley while he took notes and someone else timed. I realise that’s not actually evidence, but I think the historic charm it generates gives it heaps of credibility. 
Was there anything in the research to specifically discredit this, or am I going to be tortured by the thougt for the rest of my life?
*thought, not thougt. Remember kids, always proofread!
I have a couple of thoughts.
First, given the small amount of weight involved, I really do not think that there is a significant enough time differential between a horse, mule, or human in pulling a single pound off of the ground. Presumably, however, the test could have involved several pounds, or a few hundredweight, and this impact would be minimized.
But second, horses turning mill wheels was something they did, and it was a well-established mode of operation for a horse in an industrial works. It seems reasonable at least as a performance test.
The reference is found in many places; my specific one for the article came from Kirby, Richard S.; Withington, Sidney; Darling, Arthur B.; and Kilgour, Frederick G., Engineering in History, 1990, pp. 167-172. I would propose that it’s not up to me to discredit your recollection, rather, but perhaps you could present your citation as a counter to mine.
Someday I’d like to, rather than looking for the best/most car for the money. I’m about due for a midlife crisis. Vrooooom! That new Mustang GT is calling my name!
But I see that you have next week’s so my brilliant, next, Guest Staff Report won’t be published for a while. 
Then again, that means all the longer before I have to submit my even-more-brilliant, NEXT, next Guest Staff Report.
Correct me if I’m wrong, but don’t horses actually put out considerably MORE than one horsepower and I, a fat guy on a bicycle, can pull a horsepower or two over short distances?
I read the same thing–I recall hearing that Watt figured out that your average horse could raise a 550-pound weight at a rate of 1 foot per second, and thereby declared this to be one horsepower. But I am willing to defer to Una, Goddess of Sciency-Stuff.
Interesting article. This article goes into detail about the differences between gross horsepower and net horsepower. If you look at horsepower figures from the sixties, they will be inflated because they’re gross horsepower. It also notes that sometimes a company will understate horsepower for various reasons. The example cited of the engine used in the Corvette and the Camaro/Firebird is because the Corvette is the sports car and will always be advertised as the highest horsepower car GM sells, even when another car they sell actually has the same or more horsepower.
I almost bought a new Mustang GT, but when I saw it close up, I realized I could never sit in one and feel good about myself. That interior is so ugly it’s Kafkaesque.
Yes, I believe the original horsepower measurement was definitely an average over a duration, although the length of time of the measurement was not specified in my sources.
So what? As long as I’ve known you you haven’t felt good about yourself. 
Continuing the hijack while I try to think of something to say about horsepower vs torque so I don’t get yelled at, Motor Trend this month has “Bullitt: The Rematch,” between the Mustang GT and new Charger. First off, American four-door muscle cars, no matter their horsepower or torque, are an abomination. Second, well, there is no second point because Wife finished shopping in record time and as an old *Road & Track * reader I’m embarassed buying Motor Trend so I couldn’t finish the article. However, the Mustang trounced the Dodge in the quarter, which I see as a triumph of power to weight ratio.
I don’t know about your average fat guy, but during the Tour de France, some of my officemates and I ran some numbers on Lance Armstrong. In the mountains, he was averaging a half a horsepower just in lifting his own weight against gravity, without even considering any power lost to wind resistance or other frictional effects. Then again, Lance probably isn’t the best comparison, here.
Another excellent staff report from Una…
One thing I’ve been wondering about - could you explain the derivation of the 5252 constant?
Same reason there are 91.44 centimeters in a yard. The torque foot-pound and the horsepower weren’t created in a matching set, so you need a number to convert them.
Along the lines of what Mr. Kennedy said. More specifically, however…well, I could write the conversion out and try to look smart, but I think linking to a site where they do it for me is better. And it’s very late…
This link should explain is a bit more detail, I hope:
I don’t know about that! One particular climb wasn’t particularly long or high, from a sunken parking lot up a steep ramp to street level. The lot was about 45 feet below street level, I weighted at the time 310 pounds plus a 35 pound bike, and I timed myself at 20 seconds.
45 ft * (310 lbs + 35 lbs) = my foot-pounds of work = 15525 ft-lbf
I managed to produce that work for 20 seconds, or a third of a minute. Assuming I could continue producing 15525 ft-lbf for a full minute without dying that would mean I would produce 46575 ft-lbf/min, or 1.411 horsepower using Una’s formula.
Back then my brother, a mountain biker, wished he had my calf muscles. I pointed out that I only had them because that’s what was needed to lug around a guy who weighed twice what he did.
Una, another great article. I have one simple, silly, inconsequential question, though: Why didn’t you mention SHP (Shaft HorsePower) as another measurement of power? Just curious, since you seemed to want to be all-inclusive and stuff.
There’s all sorts of things I could have talked about regarding horsepower and torque, but I fear the wrath of Ed’s delete key…
Pretty good article, marred by I think at least one blooper:
>" Torque is a measure of the ability of an engine to do work. "
Um, well, technically, NO.
Work is force times distance.
Torque is just Force.
An engine can be putting out 550 foot-pounds of torque with the brakes fully on, that’s zero RPM, so it’s zero work. A strong rubber band could also put out that amout of force forever. Again it’s exactly zero work.
No, torque is not force. Torque is work per (some unit of angle, such as degree, radian, grad, or revolution), though it is, unfortunately, traditionally regarded as force-at-radius-x. It is the rotational analog of force.
However, Una said “ability…to do work”, not “work”.