What is Horsepower (HP)? How Horsepower Works?

There is a common concept that we encounter not only in automobiles, but also in many places from power tools to lawn mowers. Although horsepower is generally used to describe the power of automobiles, its origin dates back to ancient times. Almost everything with an electric motor is used, except cars. It also causes controversy by making different comments about it among the people.

In general, it is stated that a car with 100 horsepower is equal to the power produced by 100 horses. But it’s not exactly like that. The creator of this concept, which came to our language from the word “Horsepower”, is James Watt and it was used for the first time in 1781. While marketing the steam engines he developed, he chose to use this concept to inform his customers about machine power.

When power is mentioned in the years when it was first used, horses used in load carrying works came to mind until today. This subject, which is often confused with torque, is defined as the power that a horse can create in one minute. This value, which is found as a result of detailed calculations in technical terms, is extremely important for all vehicles and automobiles with electric motors.

What is Horsepower (HP)?

Horsepower, if we explain it in the most basic way; It is the amount of power required to move a 75 kg load 1 meter in 1 second. It has passed into our language from the term “Horsepower” in English. Horse, horse – horse; Power means power. The letters “HP”, representing horse power, are the initials of Horsepower.

Horsepower or horsepower is a term used to determine the power of automobiles and motor vehicles. The basis of this term, which is used only for automobiles today, actually dates back to ancient times. Power is defined as work done per unit time. Therefore, the power of a thing is determined not by the work it does in an unlimited time, but the work it does in a certain time.

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The expression horsepower, whose history goes back 200 years, arises from the fact that nothing but a horse comes to mind when it comes to carrying loads. For this reason, the concept of horsepower is not fully understood and is confused by many. For example, when a 100 horsepower car is mentioned, the power produced by 100 horses is understood. Horsepower, on the other hand, is a very different concept. Extensive information about what this concept is, its similarities and differences with torque power are explained in the following parts of our article.

In fact, the amount of load carried by a real horse or horse 1 meter forward in 1 second is approximately 50 kg on average. However, while the power of the engines was symbolized, for some reason, the engineers defined this weight as 75 kg. The first engineer to use the definition of horsepower was the famous inventor James Watt.

According to Watt’s approach, 1 horse can do 44.5 kJ of work per minute. Since this is the work done in a minute, it is divided by 60 seconds and the result is that the horsepower is 0.75 kW or 750 W. This result, while expressing the power of 1 horse, means that it can lift approximately 150 kilograms of coal 30 meters up in 1 minute, 15 kilograms of coal 300 meters or 450 kilograms of load 10 meters. This is horsepower.

Why is a definition like horsepower needed?

While James Watt gave information about the machines he invented, produced and offered for sale, the most curious subject of the customers was how powerful these machines were. Since everyone understands the word “power” is something else; A definition of “power” had to be made, on which different people would agree. Realizing this fact, James Watt decided to explain the power of his engines by indexing them with the power of horses, which everyone was dealing with at that time. This made things even easier.

It is known that James Watt worked for a long time to increase the performance of the steam engines he produced. He started to monitor the way horses work in mines to improve performance. In an event he observed here, he sees that the amount of load carried by the horse 1 meter forward in 1 second is 50 kilograms. Basically horsepower; It is thus accepted that the load of 75 kilograms is carried forward 1 meter in 1 second.

Searching for a way to infer the power that a single horse can produce, Watt concluded that a pony horse can do 30 kilojoules of work per minute. Increasing this value by 50 percent, Watt managed to measure the horsepower of approximately 45 kJ in one minute.

Aiming to increase the performance of the steam machine it produced after the Industrial Revolution, Watt used the concept of horsepower to market it. He began to study how horses and donkeys turned the stone in the mills to get other ideas on how he could improve performance.

He multiplied the distance traveled by the animal in 1 minute to turn the stone with the average pulling force of 80 kilograms and divided this by time. Thus, he discovered the unit he stated as horsepower. The horsepower used today is approximately equal to 735 watts.

How to Calculate Horsepower?

Based on James Watt’s principle, various formulas have emerged to calculate horsepower. According to this; A mill wheel with a radius of 12 feet is turned by 1 horse 144 times per hour, 2.4 times per minute. The force applied to the impeller at this time is 180 pounds of force.

In order to be able to calculate, it is necessary to convert the units first. According to this;

1 foot = 0.3048 meters
1 pound = 0.4536 kilograms
1 pound-force = g * 1 pound = 9.8066 m/s2 * 1 lb * 0.4536 kg/lb = 4.4482 kg.m/s2 = 4.4482 N
180 lbf = 180 * 4.4482 N = 800.6796 M

Our formulas:

Work = Force * Path ie; W = F * x
Power = Work/Time ie; P = W/t or P = (F*x)/t

If we operate according to these formulas;

P = 180 lbf * (2.4 * 2π * 12ft) / 1 minute
P = 32,572 ft.lbf/minute

Watt rounded this result to 33 thousand and stated that it was 1 horsepower. So 1 horsepower in Watt is equal to 33,000 ft.lbf/minute or 745.69 N.m/s (watts).

Is Horsepower transmitted to the wheels in the same amount under all conditions?

Since the horsepower transmitted by the engine passes through many different systems until it reaches the wheels; in different vehicles with the same horsepower; There may be variations between the forces transmitted to the wheels.

Even the number of gears in the vehicle’s components and wheel systems; It is effective in transmitting more or less horsepower to the wheels. Whether the engine is gasoline or diesel, even the size of the wheels of the vehicle changes the transmitted power.

Are Horsepower and Torque Power the Same Thing?

Today, horsepower and torque are often confused because of their similarities. In fact, this similarity is a similarity in terms of power. Let’s think this way. A weightlifter must have very strong feet. Because they must be able to stand upright and not be crushed under the weight they lift. If the kneecaps cannot carry that load, it is out of the question for the weightlifter to lift that load.

However, runners also need to have very strong feet. Because they need maximum power to take their steps faster and farther.

Well, let’s ask ourselves this question: Is the type of power needed by a weightlifter and a runner the same?

No. The strength that the weightlifter should have; While it is about being able to lift the bar better, pulling it higher; The power that a runner should have is about being able to take the steps faster and farther.

Here, when we say torque power to our minds; The strength that the weightlifter’s foot should have should come. When we say horsepower, we should think of the power of runner’s feet. While torque power is related to traction force; horsepower is more about speed. Because of this; a truck or lorry should have higher torque power than a sedan. For the same reason, a race car must have more effective horsepower than a truck or lorry.

If the trucks are given excessive horsepower, it will cause the vehicle to topple over when they reach maximum speed with tons of load. When excessive torque is given to a racing car; it will not see much effect on the racetrack. Because excessive torque has no effect on speed.