What is strength and power? What is measured by this indicator, what devices are used in this case, and how the named physical quantities are applied in practice, we will consider further in the article.
Force
In the world, all bodies of a physical nature begin to move due to force. When it is exposed, with a passing or opposite direction of body movement, work is done. Thus, a force acts on the body.
So, the bike starts moving due to the force of the legs of a person, and the traction force of the electric locomotive acts on the train. A similar effect occurs with any movement. The work of force is the value in which the modulus of force is multiplied, the modulus 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 equal to zero, then work is always done. Moreover, it can have both positive and negative values. The force will not act on the body at an angle of 90 °.
For example, consider a cart pulled by a horse’s muscular strength. In other words, the work is performed by traction in the direction of movement of the cart. But gravity, directed down or perpendicularly, does not perform 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);
- unstable (then the calculation is done with the integral).
Power
What is this quantity measured in? To begin with, we will analyze what it is. It is clear that the body begins to move due to the force that performs mechanical work. However, in practice, in addition to this, it is necessary to know how it is performed.
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 be produced. 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:
N = A / Δt.
By logical actions we arrive at the following formula:
N = Fv
that is, the product of the force vectors and the speed of motion is power. What is it measured in? According to the international SI system, the unit of measurement for this quantity is 1 Watt.
Watt and other power units
Watt means power, where one joule is produced 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 - horsepower, which is still used today. One horsepower is approximately equal to 735.5 watts.
Thus, in addition to Watt, power is measured in metric horsepower. And with a very small value, Erg is also used, equal to ten in minus the 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 happens to be of very different power. For example, an electric razor has hundredths of a kilowatt, and a spacecraft rocket has millions.
For different loads, different power is needed to maintain a certain speed. For example, a car will become heavier if more cargo is placed in it. Then the friction force on 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 eat more fuel. This fact is known to all drivers.
But at high speed, the inertia of the machine, which is directly proportional to its mass, is also important. Experienced drivers who are aware of this fact find a better combination of fuel and speed when driving, so that less gasoline is used.
Current power
What 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. Indirect method is used if necessary to measure small values. The instruments for this are an ammeter and a voltmeter connected to the consumer. The formula in this case will look like this:
P = U
With a known load resistance, measure the current flowing through it and find the power as follows:
P = I 2 ∙ R n.
By the formula P = I 2 / R n, the current power can also be calculated.
What it is measured in a three-phase current network is also not a secret. For this, a familiar device is used - a wattmeter. Moreover, it is possible to solve the problem of measuring electric power with the help of one, two or even three devices. For example, a four-wire installation will require three devices. And for a three-wire with an asymmetric load - two.