What is strength and power? How this indicator is measured, what instruments are used at the same time, and how the mentioned physical quantities are used in practice, we will consider further in the article.
В мире все тела физической природы начинают movement thanks to force. With its impact, with a fair or opposite direction of movement of the body, work is done. Thus, any force acts on the body.
So, the bike gets under way thanks to the powerthe feet of a person, and the train is influenced by an electric train. This effect happens in any movement. The work of force is the value in which the force module multiplies, the module of displacement of the point of its application and the cosine of the angle between the vectors of these indicators. The formula in this case is as follows:
A = F · s · cos (F, s)
If the angle between these vectors is not zero, thenwork is always done. At the same time, it can have both positive and negative values. The force will not act on the body at an angle equal to 90 °.
Consider for example a cart that pullshorse's muscular strength. In other words, the work is done by a thrust force in the direction of movement of the cart. But the force of gravity, directed downward or perpendicular, does not perform work (by the way, horsepower is what measures engine power).
The work force is a scalar value and is measured in joules. She may be:
How is this value measured?First, let's look at what she is. It is clear that the body begins to move at the expense of the force that performs mechanical work. However, in practice, in addition, it is necessary to know exactly how it is performed.
Work can be completed at different times.For example, the same action can be performed by a small motor or a large electric motor. The only question is how long it will be made. The quantity responsible for such a task is power. In what way it is measured, it becomes clear from the definition - this is the ratio of work for a specific time to its value:
N = A / ∆t.
By logical actions we come to the following formula:
N = F · v,
that is, the product of the force vectors and the speed of motion is power. What is it measured in? According to the international system of SI, the unit of measurement of this value is 1 watt.
Watt means power, where in one secondwork is done in one joule. 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 - horsepower, which is used to this day. One horsepower is approximately 735.5 watts.
Thus, besides Watt, power is measured inmetric horsepower. And with a very small value also use Erg, equal to ten to the minus of the seventh power of Watts. It is also possible to measure in one unit of mass / force / meter per second, which is equal to 9.81 watts.
Named value is one of the most importantin any motor, which is of very different power. For example, an electric razor has hundredths of a kilowatt, and a spacecraft rocket has millions.
Для разной нагрузки необходима различная мощность to save a certain speed. For example, a car will become harder if more load is placed in it. Then the force of friction on the road will increase. Therefore, in order to maintain the same speed as in the unloaded condition, greater power will be required. Accordingly, the engine will eat more fuel. This fact is known to all drivers.
But at high speed, the inertia of the machine is important,which is directly proportional to its mass. Experienced drivers who know about this fact, find when driving the best combination of fuel and speed, so that gasoline takes less.
What is the current measured? In the same SI unit. It can be measured directly or indirectly.
Первый способ реализуется при помощи ваттметра, consumes substantial energy and greatly loads the current source. With it, measured from ten watts and more. The indirect method is used if necessary to measure small values. Devices for this are the ammeter and voltmeter connected to the consumer. The formula in this case will look like this:
P = U · I.
With a known load resistance, we measure the current flowing through it and find the power as follows:
P = I2 ∙ Rn
According to the formula P = I2/RMr. can also be calculated power current.
How is it measured in a three-phase network,also not a secret. To do this, use the familiar device - wattmeter. And to solve the problem, what is measured by electrical power, you can use one, two or even three devices. For example, a four-wire installation will require three devices. And for a three-wire with an asymmetrical load - two.
