Power in physics is understood as the ratio of work performed for a certain time to the period of time for which it is performed. Mechanical work means the quantitative component of the effect of force on the body, due to which the latter moves in space.
Power can also be expressed as the rate of energy transfer. That is, it shows the efficiency of the automatic apparatus. By measuring the power, it becomes clear how quickly the job gets done.
Power units
Power is measured in watts or joules per second. Motorists know about horse power. By the way, before the advent of steam engines, this value was not measured at all.
Once, using a mechanism in a mine, engineer J. White set about improving it. To prove his improvement in the engine, he compared it to the performance of horses. People have been using them for centuries. Therefore, it was not difficult for anyone to imagine the work of a draft horse for a certain period of time.
Watching them, White compared the models of steam engines depending on the amount of horsepower. He experimentally calculated that the power of one horse is 746 watts. Today everyone is sure that such a number is clearly overestimated, but they decided not to change the power units.
By means of the named physical quantity, they learn about the productivity, since with its increase, the work increases over the same period of time. This standardized unit of measurement has become very common. It began to be used in a variety of mechanisms. Therefore, although watts have been used for a long time, horsepower is more understandable for many than other power units.
How power is understood in household electrical appliances
Power is, of course, also indicated in household electrical mechanisms. In luminaires, its specific values \u200b\u200bare used, for example, sixty watts. Bulbs with a large indicator then it is impossible, since otherwise they will quickly deteriorate. But if you buy not incandescent lamps, but LED or fluorescent ones, then they will be able to shine with greater brightness, while consuming little power.
Energy consumption is naturally directly proportional to the amount of power. Therefore, there is always room for product improvement for light bulb manufacturers. Nowadays, consumers are increasingly preferring options other than incandescent bulbs.
Sports power
Power units are known for more than just machinery. Power can be applied to both animals and humans. For example, you can calculate this value when an athlete throws a ball or other equipment, getting it as a result of determining the applied force, distance and time of its application.
You can even use computer programs with which the indicator is calculated as a result of a certain number of exercises done and the introduction of parameters.
Measuring instruments
Dynamometers are special devices that measure power. They are also used to determine force and torque. The devices are used in a wide variety of industries. For example, it is they who will show. To do this, the motor is removed from the car and connected to the dynamometer. But there are devices that can calculate what you are looking for even through the wheel.
Dynamometers are also widely used in sports and medicine. Exercise machines often have sensors that are connected to a computer. All measurements are made with the help of them.
Power in watts
James Watt invented the steam engine, and since 1889, the unit of measurement has become the watt, and the value was included in the international system of measurements in 1960.
In watts, not only electrical, but also thermal, mechanical or any other power can be measured. Also, multiples and sub-multiples are often formed. They are called with the addition of various prefixes to the original word: "kilo", "mega", "giga", etc.:
- 1 kilowatt is equal to one thousand watts;
- 1 megawatt equals a million watts, and so on.
Kilowatt hour
In the international SI system, there is no such unit of measurement as kilowatt-hour. This indicator is non-systemic, introduced to account for consumed electrical energy. In Russia, GOST 8.417-2002 operates with regulations, where the unit for measuring the power of electric current is directly indicated and used.
This unit of measurement is recommended to be used for accounting of consumed electrical energy. It is the most convenient form for obtaining acceptable results. Multiple units can also be used here if necessary. They look similar to watts:
- 1 kilowatt-hour equals 1000 watt-hour;
- 1 megawatt hour equals 1000 kilowatt hour, and so on.
The full name is written, as already seen, through a hyphen, and a short one through a dot (Wh, kWh).
How power is indicated in electrical appliances
It is generally accepted to indicate the mentioned indicator directly on the body of an electrical device. Possible designations are:
- watt and kilowatt;
- watt-hour and kilowatt-hour;
- volt-ampere and kilovolt-ampere.
The most universal designation is the use of units such as watt and kilowatt. If they are present on the body of the device, it can be concluded that the specified power is developing on this equipment.
Often, in watts and kilowatts, the mechanical power of electrical generators and motors, electrical heating devices, etc. is measured.This is basically the power of the current, the unit of measurement in the device of which is focused primarily on the amount of heat received, and the calculations are taken into account after him.
Watt-hour and kilowatt-hour are shown for a given unit of time. These markings can often be seen on household electrical appliances.
In the international SI system, there are units for measuring electrical power that are equivalent to a watt and a kilowatt - these are volt-amperes and kilovolt-amperes. This measurement is given to indicate AC power. They are used in technical calculations when electrical indicators are important.
This designation best meets the requirements of electrical engineering, where devices operating with alternating current have both active and reactive energy. Therefore, it is determined by the sum of these components. Volt-amperes are often used to denote the power of devices such as transformers, inductors, and other converters.
At the same time, the manufacturer independently chooses which units of measurement to indicate to him, especially since in the case of low-power equipment (such as household electrical appliances), all three designations, as a rule, coincide.
What are strength and power? What this indicator is measured in, what devices are used in this case, and how they are used in practice, we will consider later in the article.
Power
In the world, all bodies of physical nature begin to move due to force. Under its influence, with a passing or opposite direction of body movement, work is done. Thus, a force is exerted on the body.
So, the bicycle starts off due to the force of the human legs, and the traction force of the electric locomotive acts on the train. A similar effect happens with any movement. The work of force is the value in which the modulus of the force, the modulus of displacement of the point of its application and the cosine of the angle between the vectors of these indicators are multiplied. The formula in this case is as follows:
A \u003d F s cos (F, s)
If the angle between these vectors is not zero, then the work is always done. Moreover, it can have both positive and negative values. The body will not be affected by a force at an angle of 90 °.
Consider, for example, a cart being pulled by a horse's muscular strength. In other words, the work is done by the traction force in the direction of movement of the cart. But directed downwards or perpendicularly does not do the work (by the way, horsepower is what the engine power is measured in).
The work of force is a scalar quantity and is measured in joules. She may be:
- resultant (when exposed to several forces);
- not constant (then the calculation is performed with an integral).
Power
How is this value measured? First, let's take a look at what it is. It is clear that the movement of the body begins at the expense of the force that makes it. However, in practice, in addition to this, it is necessary to know exactly how it is performed.
The work can be completed at different times. For example, a small motor or a large electric motor can perform the same action. The only question is how long it will take to produce it. The quantity responsible for such a task is power. In what it is measured, it becomes clear from the definition - this is the ratio of work for a specific time to its value:
By logical actions, we come to the following formula:
that is, the product of the force vectors by the speed of movement is power. How is it measured? According to the international SI system, the unit of measurement for this value is 1 Watt.
Watt and other power units
Watt means power, where one joule is done in one second. The last unit was named after the Englishman J. Watt, who invented and built the first steam engine. But at the same time he used a different value - horse power, which is still used today. is approximately equal to 735.5 watts.
Thus, besides Watts, power is measured in metric horsepower. And with a very small value, Erg is also used, equal to ten to the minus seventh power of Watt. It is also possible to measure in one unit of mass / force / meters per second, which is equal to 9.81 watts.
Engine power
The named value is one of the most important in any motor, which can be of very different power. For example, an electric razor has hundredths of a kilowatt, and a spaceship's rocket has millions.
Different load requires different power to maintain a certain speed. For example, a car will become heavier if you put more load in it. Then the road will increase. Therefore, in order to maintain the same speed as in the unloaded state, more power is required. Accordingly, the engine will consume more fuel. This fact is known to all drivers.
But at high speed, the inertia of the machine is also important, which is directly proportional to its mass. Experienced drivers who are aware of this fact find the best combination of fuel and speed when driving so that less gasoline is consumed.
Power current
How is the current power measured? In the same SI unit. It can be measured directly or indirectly.
The first method is implemented using a wattmeter that consumes significant energy and heavily loads the current source. With its help, it is measured from ten watts or more. The indirect method is used when small values \u200b\u200bare to be measured. The devices for this are an ammeter and a voltmeter connected to the consumer. The formula in this case will look like this:
With a known load resistance, we measure the current flowing through it and find the power as follows:
P \u003d I 2 ∙ R n.
According to the formula P \u003d I 2 / R n, the current power can also be calculated.
How it is measured in a three-phase current network is also no secret. For this, an already familiar device is used - a wattmeter. Moreover, the problem can be solved by means of one, two or even three instruments. For example, a four-wire installation would require three devices. And for a three-wire with an unbalanced load - two.
Hello! To calculate a physical quantity called power, use the formula, where the physical quantity - the work is divided by the time during which this work was done.
It looks like this:
P, W, N \u003d A / t, (W \u003d J / s).
Depending on the textbooks and sections of physics, the power in the formula can be denoted by the letters P, W or N.
Most often, power is used in such branches of physics and science as mechanics, electrodynamics and electrical engineering. In each case, the cardinality has its own formula to calculate. For AC and DC, it is also different. Wattmeters are used to measure power.
Now you know that power is measured in watts. In English watt - watt, international designation - W, Russian abbreviation - W. This is important to remember, because all household appliances have such a parameter.
Power is a scalar, it is not a vector, unlike a force that can have a direction. In mechanics, the general form of the power formula can be written as follows:
P \u003d F * s / t, where F \u003d A * s,
From the formulas it can be seen how instead of A we substitute the force F multiplied by the path s. As a result, power in mechanics can be written as force multiplied by speed. For example, a car with a certain power is forced to slow down when driving uphill, as this requires more power.
The average human power is taken as 70-80 W. The power of cars, airplanes, ships, missiles and industrial installations is often measured in horsepower. Horsepower was used long before the introduction of watts. One horsepower is equal to 745.7W. Moreover, in Russia it is accepted that l. from. equal to 735.5 watts.
If you are suddenly accidentally asked 20 years later in an interview among passers-by about power, and you remember that power is the ratio of work A, performed per unit time t. If you can put it that way, pleasantly surprise the crowd. Indeed, in this definition, the main thing to remember is that the divisor here is work A, and the dividend is time t. In the end, having work and time, and dividing the first by the second, we get the long-awaited power.
When choosing in stores, it is important to pay attention to the power of the device. The more powerful the kettle, the faster it will heat the water. The power of the air conditioner determines how much space it can cool without extreme engine load. The more power of the electrical appliance, the more current it consumes, the more electricity it will spend, the more the electricity bill will be.
In general, electrical power is determined by the formula:
where I - current strength, U-voltage
Sometimes even it is measured in volt-amperes, writing it down as B * A. The total power is measured in volt-amperes, and in order to calculate the active power, you need to multiply the total power by the efficiency (efficiency) of the device, then we get the active power in watts.
Often, devices such as an air conditioner, refrigerator, iron work cyclically, turning on and off the thermostat, and their average power over the total operating time may be small.
In alternating current circuits, in addition to the concept of instantaneous power, which coincides with the general physical, there are active, reactive and apparent powers. Apparent power is equal to the sum of active and reactive power.
To measure power, electronic devices are used - Wattmeters. The unit of measurement Watt got its name in honor of the inventor of the improved steam engine, which revolutionized the power plants of that time. Thanks to this invention, the development of industrial society accelerated, trains, steamships, factories appeared, using the power of a steam engine to move and manufacture products.
We have all come across the concept of power many times. For example, different cars have different engine power. Also, electrical appliances can have different capacities, even if they have the same purpose.
Power is a physical quantity that characterizes the speed of work.
Respectively, mechanical power is a physical quantity that characterizes the speed of mechanical work:
That is, power is work per unit of time.
SI power is measured in watts: [ N] \u003d [Watts].
1 W is 1 J work done in 1 s.
There are other units for measuring power, for example, such as horsepower:
It is in horsepower that the power of a car engine is most often measured.
Let's get back to the formula for the power: The formula by which the work is calculated is known to us: 
Therefore, we can transform the expression for cardinality:
Then, in the formula, the ratio of the displacement modulus to the time interval is formed. This, as you know, is the speed:
Just note that in the resulting formula we use the velocity module, since we have divided not the movement itself, but its module for the time being. So, power is equal to the product of the modulus of force, modulus of speed and the cosine of the angle between their directions.
This is quite logical: say, the power of the piston can be increased by increasing the force of its action. By applying more force, he will do more work in the same time, that is, he will increase the power. But even if you leave the force constant and make the piston move faster, it will undoubtedly increase the work done per unit of time. Consequently, the power will increase.
Examples of problem solving.
Objective 1.The power of the motorcycle is 80 hp. Moving along a horizontal section, the motorcyclist develops a speed of 150 km / h. At the same time, the engine runs at 75% of its maximum power. Determine the frictional force on the motorcycle.
Objective 2.The fighter, under the influence of a constant thrust force directed at an angle of 45 ° to the horizon, accelerates from 150 m / s to 570 m / s. In this case, the vertical and horizontal speed of the fighter increases by the same value at each moment of time. The mass of the fighter is 20 tons. If the fighter accelerated within one minute, what is the power of its engine?
If you need to bring the units of measurement of power into one system, our conversion of power - an online converter will come in handy. And below you can read how the power is measured.
Automotive manufacturers from different countries measure the power of their vehicles in different units. What for? You will find out the answer below.
When reading an article about cars, be sure that you will always come across this data. With which? With car power data. Car engine power is one of the most important indicators, relevant at any time, in any situation. From both practical and theoretical points of view.
Always up to date. According to statistics, one of the most interesting pieces of information about new products for readers lies precisely in the power of car engines. Thus, at a subconscious level, people compare models, their advantages and weaknesses relative to each other, only in one parameter - the power of the motor.
Power per se is a measure of how quickly and how far an engine can, through physical work, propel a car forward using torque. In mechanical engineering, this phenomenon is summarized by the concept of the amount of "work" that the power unit of a car must perform in order to propel the car forward. As a measure of measurement, such work has received many different units over time. We will take a closer look at some of them today.
Kilowatts (kW)
From a technical point of view, this form of measurement is the most versatile method for calculating power. It is used by engineers all over the world.
Watt is a SI unit of measurement (International System of Units), which means how much power will be required to do work in 1J per unit of time.
It is mainly used by professionals as a more "correct" power indicator from the point of view of fundamental science. As a unit of measurement in the automotive industry is used mainly in the Southern Hemisphere, so it has historically developed.
The method of measuring power in kilowatts on cars mainly occurs by finding the amount of torque transmitted from the wheels on a dynamometer, then this equation is used for calculations:
Kilowatts have become a modern measure for fixing the power output of cars and perhaps in the future they will become a generally accepted global measure. At least if you look at any of the official figures offered by automakers, you will definitely see the units of kW of power of internal combustion engines on par with horsepower.
Moreover, as the hype around electric cars begins, the introduction of this form of measurement will become even more justified, because the amount of work produced by an electric motor is measured using kWh (kilowatt-hours), which determine how long an electric motor can produce a certain amount energy, for example, for driving a car.
Horsepower (hp)
Introduced into everyday life by the "maestro" and part-time the creator of productive steam engines - Mr. James Watt - this unit of power, based on horsepower, is somehow alive to this day, carrying the calculations of a brilliant engineer through the centuries. It is the main unit for measuring the power of cars in many countries, including Russia, it is used not only as a measurement of the power of an internal combustion engine in official documents for car models, but also for calculating taxation in the automotive sector, for example, calculating transport tax.
So what is horsepower (hp)? How did it come about and how is it calculated? How was her appearance related to horses?
Scotland, inventor James Watt has brought to mind his first steam device that could help hundreds of industrialists and artisans in their everyday work. And it seems that the engine was good for everyone, but how to explain this to the townsfolk? The answer suggested itself, it was necessary to compare the work of the most widespread at that time "power device" (horse) with the work of a new machine. No sooner said than done, Watt sat down to count.
COUNTING AND COMPARISON OF UNITS OF MEASUREMENT
In most European countries, horsepower is defined as 75 kgf m / s, the power expended with a uniform vertical lifting of a 75 kg load at a speed of 1 meter per second with an acceleration of gravity of 9.8 m / s.
In the International Metric System, SI is officially measured in watts. 1 h.p. (metric horsepower) is equal to 735 W or 0.73 kW.
In turn, 1 kW is equal to 1.35 hp.
Moreover, the measurement system in the United Kingdom, as well as in the United States, equates horsepower (hp) to 745 watts, which is why there is a slight discrepancy with European "horses". Thus, 1 hp. in the USA is equal to 1.0138 hp. from Europe.
For example, the power of a 3.8 liter engineNissanGT-R is 570 h.p., in kilowatts it will be equal to 419
, in hp 577
units.
See also:
How James Watt introduced steam engines and horsepower
Now, no one knows for sure how strong the horses that participated in Watt's experiments were, whether they were in their prime or they were old nags. However, several legends have survived.
According to one of which, a certain brewer, the first buyer of Watt's steam unit, probably in order to bring down the price of the inventor's car, decided to hold a competition. A horse in a brewery powered a water pump, and a brewer wanted to buy a steam engine instead.
In order to win for sure, an unfair industrialist chose the strongest horse for competition and, by manipulating the whip and other tools to increase labor productivity, squeezed the maximum efficiency out of the poor beast. In response to the challenge, James Watt, using his machine, exceeded the work performed by the horse by 1.5 times, according to some sources, which was taken as a sample of a metal device that worked on steam.
The second legend, on the contrary, tells us that Watt himself slightly "twisted" the calculations in his favor. He needed this in order to convince the intractable owners of coal mines to switch from draft horses to steam engines. In the 18th century, the coal from their mines was lifted by horses with a rope through a system of blocks. After calculating the performance of the average horse, Watt applied a factor of 1.5 multiplying the resulting number, making his machine easily outperforming any horse doing the same job.
Since horsepower has spread significantly across the globe due to the simplicity of calculations and understandability for users, various types (definitions) of horsepower have appeared: metric horsepower, mechanical horsepower, boiler hp, electric hpand water horsepower.
Perhaps in some articles and news, both foreign and domestic, you have repeatedly come across incomprehensible abbreviations, for example: nhp,rhp, bhp, shp, ihp, whp... What do they mean?
Nhp orrhp,Nominalhorsepower,ratedhorsepower- net power, used to estimate the power of steam engines.
Bhp,Brakehorsepower- the effective power in hp, the power “removed” from the crankshaft of the internal combustion engine, does not take into account the power loss from the gearbox and transmission of the vehicle.
Shp,Shafthorsepower- engine power on the shaft, this is the power supplied to the propeller shaft, to the turbine shaft or to the output shaft of an automobile gearbox. Gross
Ihp,Indicatedhorsepower- Indicated power in hp, this is the theoretical power of a piston engine, determined by the sum of power from the crankshaft, effective power, and energy consumed for friction.
According to the operation of the apartment electricity meter, it can be traced that the winding up of kilowatt-hours occurs the faster, the greater the load is supplied to the network. This is one of the ways in which power is measured. There are several varieties of the indicator, indicated by the first letter of the English watt - W. The amount of energy consumption depends on the parameters of the electrical circuit of the dwelling - it is directly proportional to the power of the connected pantographs.
Types of electrical power
The physical quantity W represents the rate of change, transmission, consumption and transformation of energy of the system under consideration. Specifically, the definition of power sounds like the ratio of the work performed in a certain period of time to the time interval of action: W \u003d ΔA / Δ t, J / s \u003d watt (W).
With regard to the electrical network, we are talking about the movement of charge under the influence of voltage: A \u003d U. The potential between two points of the conductor is the indicator of the energy of motion of a single nucleon. The full work of the flow of the entire number of electrons is Ap \u003d U * Q, where Q is the total number of charges in the network. In this case, the power formula takes the form W \u003d U * Q / t, the expression Q / t - electric current (I), that is, W \u003d U * I.
In energy, there are several terms W:
The nature of the installed equipment predetermines redundancy Wр, when capacitive devices prevail and the potential increases, or deficiency, if the mains inductance prevails (voltage decreases). Using the principle of the opposite action, devices have been developed that make it possible to compensate for the harmfulness of Wp and improve the quality and efficiency of energy supply.
Influence of network parameters on kilowatts
From the formula W \u003d U * I, it can be seen that the power depends simultaneously on two characteristics of the power system - voltage and current. Their influence on the network parameters is parity. The process of generating electrical power can be described as follows:
- U is the work spent on moving 1 pendant;
- I is the number of charges flowing through the conductor in 1 second.
According to the calculated value of W, the consumed energy of the network is determined, multiplying the amount of power by the time it is spent. By changing one of the parameters W in the direction of decreasing or increasing, it is possible to keep the energy of the system at a constant level - to obtain a high amperage at low voltage or a large potential of the network with a weak movement of coulombs.
Converting devices designed to change parameters, called voltage or current transformers... They are installed at step-up or step-down electrical substations to transfer energy from a source to consumers over long distances.
Load measurement methods
You can find out the power of the device by referring to its instructions or passport, and if not, look at the nameplate attached to the case. If there is no manufacturer data, then other methods are available to determine the energy of the equipment. The main one is measure the load with a wattmeter (a device for recording electrical power).
According to their purpose, they are divided into 3 classes: direct current and low-frequency (LF), optical and high-pulse. The latter are referred to as the radio range and are divided into 2 types: included in the line break (passing power) and mounted at the end point of the route as an agreed (absorbed) load. According to the method of communicating information to the operator, digital and analog devices are distinguished - indicating pointer and self-recording. Brief characteristics of some meters:
In addition to the help of special devices, the power is recognized by applying the calculation formula: an ammeter is included in the break of one of the supply wires, the current and voltage of the network are determined. Multiplying the values \u200b\u200bwill give the desired result.