Can a horse do a horsepower?

October 22, 2006 3:49 PM

Is it true that a horse is not capable of doing a horsepower worth of work? (And since horses are supposed to have such a high power to weight ratio are there any other animals that can do so?)

I school I heard the story that James Watt asked some pony managers at a coal mine how much their charges could do and that - perhaps sensing imminent redundancy - they exagerated somewhat. Any evidence for or against this story?

I also read (I think in New Scientist a few years ago) that horses have somewhat freaky physiology that allows them to deliver way more sustained power than any other animal of a similar body weight. Is this true?

We are talking about 33,000 foot pounds per minute (in whatever combination of weight and speed of movement) or about 746 watts I believe.

posted by rongorongo to science & nature (8 comments total)

Even a human can producer one horsepower, though only briefly.

The wikipedia entry on Horsepower has more info.
posted by atomly at 3:52 PM on October 22, 2006

1 horsepower is about 746 watts, which is a rate unit, equal to 1 Joule per second. Cyclists, who have the tools to measure these things, can put out sustained effort in the range of 2-400 watts, and pros can put out much more, during things like long hill climbs. They can even peak above 1000 watts (albeit only for a few seconds). Assumedly, horses can do much more than that.
posted by The Michael The at 6:21 PM on October 22, 2006

A good cyclist could generate .4 horsepower indefinitely. I find it hard to believe a horse couldn't produce at least 2.5 times a cyclist.

whether they could do wheelies is a different matter
posted by Rumple at 6:27 PM on October 22, 2006 [1 favorite has favorites]

Yeah, but horses can't ride bikes. Doesn't that impact their maximal efficiency?
posted by knave at 6:32 PM on October 22, 2006

Can't ride bikes, or won't ride bikes? Hmmmm?

I'm not sure how their noncyclisme affects their horsepower though.
posted by Rumple at 6:36 PM on October 22, 2006

Does it help to know that an acre is "approximately the amount of land tillable by one man behind an ox in one day."? No, probably not.
posted by jepler at 7:13 PM on October 22, 2006

I've never thought that one horse-power was really the same as the power output of a horse, but I've always thought that it was wrong the other way. Two examples :

1. We own a one horse mowing machine (made around 1914, much less common than the 2 horse models), which has a 42 inch cutter bar. The rule of thumb I've always heard for tractors and sickle bar mowers is that you need one hp per foot of cutter bar, so this should require 3.5 hp. But even I can pull it for short distances !

2. A one horse plow is typically one bottom 8 - 10 inches wide. This is the kind that the horse or mule pulled while a man walked behind guiding the plow. The tractor power estimate for plows is about 10 hp per foot of plow bottom, which is even further off (part of that is the faster speed of the tractor, though).

Also, mules are bred to have the strength of a horse and the brains and toughness of a donkey (horses are quite dumb in comparison, but I'm speaking as a mule owner).
posted by rfs at 8:28 PM on October 22, 2006

Whoa, thanks Rumple. Paul MacCready is my new hero.
posted by Eamon at 9:53 PM on October 22, 2006