I’m confused about the meaning of this word. Is it how much a horse can pull translated into how much the engine can pull? Also, what is the actual “metric”? Why do we still use this? It seems archaic.
Also, what type of horse was originally used to get the measurement?
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Horsepower is the average output of a horse throughout a day. Horses can still outpace horsepower fairly routinely, just not in a sustained way. When an engine is said to have “100 horsepower”, it means it has as much output as 100 horses on average
It is indeed an archaic unit of Power (approx. 740 watts), but like many archaic units it survives because it sounds cool and only serves as a subjective comparison of “which is better”, so it’s actual objective value isn’t really important.
I don’t know if it’s even originally related to horses, but there’s probably a source on the internet that would explain.
Before steam engines, horses were used to pull plows and cranes and mills.
When steam engines started displacing horses in these applications in the 1800s it was necessary to measure the working capacity of these machines in a way that people understood.
The obvious point of comparison is the horse they’re replacing, so the unit “horsepower” was developed to approximate the working capacity of a draft horse.
This isn’t a horse at full sprint or max load, it’s what a working horse can calmly do all day long.
One horsepower is the power to lift 550 pounds by 1 foot per second in a horse-drawn crane.
Horsepower is a calculated metric, based on the torque output of an engine at any given RPM
Horsepower = Torque * RPM / 5252
The term has evolved over time, but was originally used to describe the amount of power output a steam engine could provide. The method of calculation on dynamometers has also changed, gross vs net, back in 1971.
1 Horse does not necessarily produce 1 horsepower, either. It was an averaged metric over a day’s time. If a horse really exerts itself, it can produce upwards of 15hp (think sprinting vs long distance running).
How does it relate to engines? Some engines produce considerable torque, but can’t maintain that torque throughout the rpm range (high torque, low horsepower, like diesels). Some engines produce considerable torque, but only at high rpm (high horsepower, low torque, such as a sportsbike or smaller displacement engines). Some engines (my favorites) produce gobs of torque at low and high rpm, having a “flat curve” (high horsepower and high torque, such as a supercharged V8). This is a *greatly simplified* explanation of how it all works and is calculated.
Here’s an answer. Torque is kinda like how strong an engine is a certain instant. Like if you pedal your bike really fast the max torque is like the hardest you pedaled out of all your pedals. But horsepower is more like adding up all your pedals over time and dividing them to get a number we can compare across vehicles or machines. Horsepower very specifically is a measurement that involves TIME and POWER.
A horsepower is a unit of power. Not so much the force you can pull, but the energy output per second. It may translate to the force you can pull, or to the speed you can reach, depending on what gear you use; different gears use power for speed or for force.
A horsepower is the average power of one draft horse during routine, non-strenuous activity. Measuring the engine in these units compares it with a horse, how many times is the engine more powerful than a horse.
Horsepower is a measure of power. It’s the amount of power required 550 pounds 1 foot in 1 second.
A guy named James Watt made up the measure. He measured how quickly a horse could turn a wheel at a mill and named that “horsepower”. Today, we usually measure power in units called “Watts”. Like pounds, gallons, and ounces, there are a few different definitions of horsepower that are slightly different amounts of power (because there’s different ways of measuring it in different situations), but 1 horsepower is roughly 745 Watts.
In terms of a car or truck, the horsepower describes the power of the engine, or how quickly it can move the vehicle. More horsepower means the car can move more weight faster.
If you are engineering an engine for some reason, you are usually worried first about torque. Torque is a unit that measure twisting power, in SI we call it a newton meter. Or, one newton of force applied to an arm that is one meter long. The more of those newton meters, the more you can twist. The more you can twist, the heavier the vehicle you can move.
That is all well and good, but it leaves out how we measure how fast two vehicles can go assuming similar weight and similar torque. That measure is horsepower which is calculated as h = torque * RPM / 5252. So if you have an engine that for each rotation of the crank, produces X amount of torque and can max out at 7,000 RPM, that vehicle will have higher horsepower and will go faster than an engine that produces X amount of torque but taps out at 5,200 RPM. Race engines, famously, rev really high. I think an indy car revs up to 20,000 RPM.
There is more to this, like if you are designing a diesel that should go 85 mph while towing 7,000 kilos, that engine will likely have something like 350-400 horsepower (don’t need more than that to go 85 mph) but will produce something like 1200 newton meters of torque and taps out at some low RPM. It doesn’t benefit you at all to have twice the horsepower and half the torque, the stated purpose is to tow.
Now you are the engineer developing a 5.0 liter 10 cylinder motor for the Audi R8. You have the inverse requirement, you will literally never tow so you only really need enough torque to handle the weight of the vehicle plus two passengers and gas. You need horsepower to make it go nice and fast. So that engine produces 600 horsepower and 565 newton meters of torque while it red-lines at 8,100 RPM.
> Also, what type of horse was originally used to get the measurement?
Smallish ponies working at a comfortable pace they could keep up for hours and hours.
Once upon a time they used horses to pull stuff.
When locomotives were invented, they invented a unit to say how powerful the engine was. “the power necessary to lift a total mass of 33,000 pounds one foot in one minute” was chosen as a unit and named horsepower. It was more or less what an horse would do in average without getting tired. Basically, you could replace 10 horses with 10 horsepower engine. It was quite a wild approximation but, hey, at least we have a unit.
It has nothing to do with the real horse if pushed to the limit, a real horse in a sprint is actually delivering something between 4 and 8hp. Im digressing. So horsepower was the name of a unit used to promote and compare steam engines.
Anyway, power is defined as “things done per second”, like, how many kilograms can you lift one meter in a second. There are many units to measure it, and the horsepower (again, not an actual horse of power) is the hystorical favorite. Nowadays we prefer the Kilowatt as a unit, it’s better for math and it can be used in multiple fields.
Anyway, your car engine has a maximum power, this power defines the maximum things per second your car can do.
Example: your car is stationary and you floor the gas to accelerate. A 100 Hp engine will make your car go faster by a certain amount per second. If you double the horsepower you will add twice as much speed per second, aka, you double your acceleration.
If you go uphill, more power means you will be able to go uphill faster, or carry more load uphill for the same speed.
So, when you buy a car, the horsepower is a useful unit to determine what your car will be able to do. If you want to save money, you can get a small engine with less power, it will cost less to buy and will consume less fuel. However, if you want a sporty car you want to have more power.
Once you have a car, you are stuck with whatever power it has. But before buying, its an important stat to look.
Broadly:
50-100hp economic to standard car. Good but if you use this economic car to race uphill your engine will really suffer and overheat.
100-200 standard to quite quick car, will have no trouble quickly overtaking any vehicle, even uphill. Also will suffer less in hot climate and in the mountain.
200-1000 hp: something between ok you are rich and you have spare money for gas, and you dvrooom vroom and you can go from stationary to breaking the speed limit, crash and go to jail in a matter of seconds. Not practically useful but feels powerful.
2000-20000 kw you are actually driving a locomotive or a set of locomotives.
100000 hp is roughly a Boeing 777
212000 hp… sry that’s not a car that’s USS IOWA aka “it’s nice to have guns but it’s even nicer if no one can run away from you”
Rough conversion: 1 hp = 3/4 kw. 100hp=75 kw and so on.
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