Every student knows that the values of all physical quantities are currently represented by the standards of the International System of Units, or SI. One of the important quantities in physics is force. Consider the question of what is its unit of measure in SI, as well as in other commonly used systems.
What is power?
Before considering the question of the unit of measurement of force in the SI system, we will understand the concept of force itself.
In classical physics, it is understood as a quantity that is capable of changing the nature of the motion of an object, for example, its direction of motion or speed. This physical quantity, together with energy, determines the intensity of any interactions that exist in nature.
When people talk about power, it is customary to consider it from two points of view:
- The nature of the origin of the force, for example gravitational, electrical, or mechanical.
- The result of her action, that is, how she influenced the movement of the object. In this understanding, they mean the use of Newton’s second law.
Examples of the manifestation of force in action are the movement of a car (a mechanical force that forces its wheels to rotate) or the ball falling from a certain height (gravity).
History reference
The emergence of the concept of power dates back to the times of philosophers of ancient Greece. In particular, Archimedes believed that any body is at rest if other bodies do not influence it, that is, the philosopher considered force in statics.
The first definition of this physical quantity from dynamic positions is attributed to Galileo (XVII century), who, unlike Archimedes, believed that the lack of interaction with other objects of the body in question would not change its inertial motion.
Isaac Newton developed the modern concept of power in his writings. He defined this concept in detail, including it in all the laws of classical mechanics. So, Newton determined that the intensity of interaction of absolutely any bodies having a finite mass decreases as the square of the distance (the law of universal gravitation). Only one century later (the end of the 18th century), Henry Cavendish, using torsion scales, was able to measure the gravitational constant, which was introduced by Newton. For Newton’s listed merit in physics, the unit of force in the SI system was named after his last name.
In modern physics, the concept of force is mainly used to describe macroscopic objects. In quantum mechanics and elementary particle physics, they often operate with the concept of "energy".
International System of Units and Newton
By this name is meant a system of measures and quantities, which is briefly denoted by SI (from the French. Système International). It is based on 7 basic physical quantities (ampere, kelvin, second, candela, kilogram, meter and mole). SI was adopted in 1960, and in 1971 the last fundamental value of "mole" was added to it.
In the SI system, the unit of measurement of force is Newton. It is understood as such a category which, acting on a body with a mass of 1 kg, accelerates its movement by 1 m / s for every second of time. In Russian, the designation of Newton [H] is accepted, in Latin it is written as [N].
Application of prefixes approved in SI to the basic units of measurement allows to obtain their fractional or large values. For strength, it can be, for example, μN (micronewton, 1 μN = 10 -6 N), mN (millinewton, 1 mN = 10 -3 N) or kN (kilonewton, in newtons it is 1000 N).
It is curious to note that Newton is not among the 7 fundamental units of measurement of force in the SI system, so it is a derived unit. In particular, 1 [N] = 1 [kg * m / s 2 ], that is, it is expressed in kilograms (mass), meter (distance) and second (time).
The work of force in the SI system
It has already been mentioned above that the concepts of power and energy are closely related to each other. This connection can be clearly expressed through work. In physics, work is the value obtained as a result of the product of the modulus of force that acts on the body in the direction of its movement, by this very movement. In mathematical form, we can write: A = F * l, where F is the force model, l is the distance that the body moved as a result of the action F.
In SI, force is measured in Newtons, and distance in meters, so work will be expressed in N * m. However, this quantity has its own name: joule (J), that is, it is expressed in the same units as energy.
What instrument measures force?
To measure the force in Newtons, Kilonewtons, Millinewtons, a device called a dynamometer is used. It was invented by Isaac Newton. The device is a spring mounted on a graduated ruler. Since the tension of the spring is described by Hooke's law, that is, it is elastic, the force is always directly proportional to the magnitude of the spring elongation. This fact is used in the dynamometer when calibrating it.
In addition to the dynamometer, torsion scales are used to measure too small forces, the main element of which is the so-called torsion pendulum. The force measurement using these weights is based on the elastic shear deformation of the working element.
Strength in other unit systems
The SI system is used all over the world and in all areas of research, however, in some areas, due to historical reasons or simple usability, units of measurement from other systems continue to be indicated. The conversion of all of them into SI units is also standardized.
One of the most popular is the GHS system (centimeter, gram, second). This system was proposed back in 1832 by the German scientist Gauss. In it, the force is measured in dyne (dyne), 1 dyne is equivalent to 10 -5 Newtons. GHS is often used to describe electromagnetic phenomena, since in its presentation form many laws look simpler than in SI units.
Another system of units, which is called technical, has often been used to describe engineering processes. In it, force is the fundamental unit through which mass is determined. It is called kilogram-force or kilopond. A kilogram-force is such an intensity of impact on a body weighing 1 kg, which is equal to the force of gravitational attraction of this body by the Earth, that is, 1 kilopond = 9.81 Newton. With the advent of SI, the technical system of units has practically ceased to be used.