# how many horsepower does a horse have?

Discussion in 'Highly Technical' started by Atheus, Nov 24, 2007.

1. ### Atheus Diamond Member

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You might naturally and understandably reply, 'one you fool', but think about it for a minute. A little vespa scooter produces about 10 horsepower. If this is actually 10 times the power of a horse then a vespa weighed down to 400kg (my guess at the weight of a horse) should not only be able to move itself at considerable speed, but should also be able to beat up to 9 horses in a tug-of-war. Obviously it can't. Can it?

The first thing that comes to mind is traction. We could eliminate this factor by running the vespa engine in a 400kg rail carriage on toothed rails, giving it massive traction - would this allow it to pull the horses backward? Instinctively it still seems ridiculous.

So what's wrong? Does a horse have more than one horsepower? Is it really all down to traction? Or am I confusing horsepower with torque? Or something equally dumb?

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3. ### Born2bwire Diamond Member

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It is respresentative of the average power output of a horse, that was how it was first defined though the actual power is something like 550 ft-lb/s. I don't know why you find 10 hp to be too small to get the vespa up to speed. Horses can typically reach speeds of 30-40 mph or more. Not that big of a stretch to imagine a little vespa being able to reach and maintain highway speeds.

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4. ### Atheus Diamond Member

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If it weighed the same as a horse could it reach those speeds? And what about the tug of war situation?

/edit: maybe it's all about gearing - a horse has infinite gears, so it can start incredibly low to pull off the line in a tug of war, but a bike only has a choice or 4 (or 5 or whatever) so it has to start much higher and cannot use as much of its power.

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5. ### Peter Elite Member

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'horsepowers' as applied to motor vehicles originally was a tax thing. Coaches were taxed by number of horses, so when those smartarse engineers showed up with zero-horse coaches, the tax authorities had to make some 'equivalent' up so they could tax them anyway.

That's how e.g. the Citroën 2CV got its name - Deux Chevaux, two horses.

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6. ### Born2bwire Diamond Member

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Torque, gearing, and all that are forces and will not affect the amount of power that is used past maybe efficiencies of using one gear over the other (that is as long as the outputed force is enough to overcome static friction). All they are saying is that the vespa's motor can output the same amount of power as 10 representative horses. Tug of war is a different matter as that is about force, which is not what hp is really measuring.

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7. ### lyssword Diamond Member

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I think horse has a lot of torque, but only 1 horsepower due to "rpm" Horsepower is basically how much work you can get done in a certain time period. If you made some special pulleys/gears and you are not losing much power on friction, then 10hp motor will outpull lets say 5 horses. A winch with 4.6 hp motor can pull 12000 lb, I doubt 2 horses would be able to pull that much (maybe 4 would be able to ) My examples though, are for side-by side comparison, not tug of war, but it probably applies to tug of war too.

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8. ### natto fire Diamond Member

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It really depends on the breed and health of the horse. As born2bwire said, 1 horsepower is the ability to raise 550 pounds of mass 1 foot in 1 second, so it is a set number, where as horses are more varied in their strength. Your scenario would be determined by many factors, especially the power curve of the motor in question.

Because horses and vehicles use different forces for locomotion, it would be hard to make a direct comparison.

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9. ### silverpig Lifer

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We did a very simple and crude experiment in my high school science class years ago.

We timed ourselves running up the stairs from the bottom floor to the third floor. We measured this height. Then we multiplied our weight times the height we climbed, and divided by the time it took, then converted into horsepower. I remember scoring just over 1 hp.. 1.01 or so.

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10. ### KIAman Diamond Member

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Also remember that the horsepower of the Vespa is at its "peak" RPM. The horsepower curve starts very low for typical gas engines (about 10% of its peak) and gradually increases the RPMs reach the peak speed and then a sudden "peak" of horsepower of 10 at the optimum RPM. Average horsepower is probably closer to 8.

In a tug of war contest, the horses will win hands down. Why? Gearing. The gearing/clutch is probably rated a little over the engine's power spec so even if you popped the clutch at it's optimum RPM the gear, clutch or engine will bog and die.

Of course if you modify the Vespa with very low gearing (1st gear is something like 14/1) and make it like 1000/1, the Vespa will win.

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11. ### BrownTown Diamond Member

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The answer is "1HP", but that is an AVERAGE amount of power a horse would produce working for hours at a time, In a sprint I am sure a horse could get 10+ horsepower. The original definition is based on the amount of coal you could get out of a mine. So if you had 10 horses and knew the depth of the mine that would tell you how many pounds of coal would be extracted in an hour. Obviously its not an exact measurement, different breeds and ages of horses would have a wide range of power outputs, but the term"horsepower" really is based on the power output of a horse.

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12. ### wwswimming Banned

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without looking it up, i remember this conversion -

1 hp = 750 ft-lbf/ second.

for example, if you're riding your bike up to Skyline,
and climbing at the rate of 1 vertical foot per second,
and you and your bike and water bottle together
weigh 187.5 pounds, you're doing about 1/4 horsepower
worth of work.

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13. ### jagec Lifer

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I got 1.5, sucka!
That was actually a fun experiment.

"Horsepower" was originally designed as a measure of the work done by a horse, but you have to remember that (a) this was considered to be the work that a draft horse could sustain throughout the day, and these horses weren't always that well fed or treated. A race horse taking off from the gate would develop WELL above 1 hp. and (b)horses were significantly under-rated by the guy who came up with the measure, since IIRC he had financial interests in the gasoline engine. I could be wrong about this.

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14. ### d33pblue Senior member

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Its actually 550 ft-lbf/second

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15. ### d33pblue Senior member

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This can be viewed as a balance of FORCE equation, NOT a power equation. If two entities are locked and pulling in opposite directions, the one that "wins" will be able to generate the most effective force in the opposite direction.

Now, with that said, a horse can generate a maximum amount of force from a stand still, a scooter cannot. 10 horses connected and pulling in the same direction against an equal force can more or less generate the maximum FORCE that 10 horses are able to generate. A scooter on the other hand can generate VERY LITTLE force from a standstill (this is what we think of as "low end torque"). Only when the scooter gets revved up to a high RPM does it generate a larger amount of force (high end torque, most commonly thought of as "horsepower").

Now, you were correct to think about gearing. With gearing, you can multiply the torque of the scooter's motor to generate (more or less) as much force as you would like. The downside is that when torque goes up, speed goes down (given that power remains constant for a given RPM, regardless of what gear the scooter is in). With a low enough gear, a 10HP scooter could theoretically overpower 50 or more horses (given that its transmission and internals were strong enough to hold up) - it would just be very slow in doing so.

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16. ### Biftheunderstudy Senior member

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Somewhat related, there was a top gear episode where they had a British tug-of-war team pulling against some merc with 700+ hp. Needless to say the team won, the problem was the car couldn't transfer all the force to the pavement, and when the wheels lost traction it was all over. The top gear top tip was something like "If you want a car with the most horsepower, buy 10 big burly blokes instead"

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17. ### Peter Elite Member

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Yeah, that'll help explaining ancient units of measure ...

Besides, it's "it's" not "its"

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18. ### BrownTown Diamond Member

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You are wrong about this, the term "horsepower" was around well before the gasoline engine. Additionally according to wikipedia 1HP is MORE than the average horse can put out.

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19. ### Aluvus Platinum Member

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Well that settles it then.

Someone needs to look up Horsepower from a horse, from a 1993 issue of Nature.

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20. ### jagec Lifer

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OK, I was wrong about the first point.

But I don't know about the second...I can buy that a horse cannot SUSTAIN 1 hp, but I really doubt that they can't output more than that instantaneously. I mean, during one of those high school experiments I developed 1.5 hp, and that was taking direct measurements...if a horse gets startled and sprints up a hill, I bet it develops much more than 1 hp.

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21. ### BrownTown Diamond Member

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Just read the wikipedia entry, says that the maximum instantaneous power output is ~15HP for a top of the line horse. The <1HP is the average over several hours.

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22. ### steppinthrax Diamond Member

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The reason why we use horsepower for automotive engines is because about a hundred years ago when engines were first developed they were marketed to farmers. Of course these people were use to how a horse would work in the fields. Rather then telling a farmer this engine is 1200cc or 2.9L displacement (which meant absolutley notthing to them) they used the term horse power as the amount of work the engine could do if it were physical horses on the field. Horsepower though is an unscientific term like fahrenheit which is very unscientific as well. The english system is another example. Read about how foot and inches were created.

Brigs and straton have stopped using horsepower when marketing their new product but Torque instead. They say horsepower in certian situations mean absolutley notthing in certian situations. Such as a log splitter or pressure washer.....

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23. ### Howard Lifer

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Give the horses the advantage of gearing...

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WTF

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25. ### KIAman Diamond Member

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FYI, horsepower is just torque over time. Who cares what we call a unit of measurement, doesn't mean it's inscientific. I could call a bork something that is 1.6 meters long and that'd be fine.

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