What Are Physics Forces?

Force is one of the basic concepts in mechanics. It is an external cause that causes an object to obtain acceleration or deformation. In dynamics it is equal to the product of the mass of the object and its acceleration.

When the concept of force forms a brief history of pushing and pulling objects, you can intuitively realize the fuzzy concept of "force". When the pushed and pulled object moves and the object glides, it gradually slows down due to friction and finally stops, reflecting the effect of force. The ancient Chinese text "The Classic of Mo" summarized this concept as "force, because of its shape, and its strength." That is to say, force is the reason that makes objects move up. Therefore, force is naturally reflected in human consciousness. But people have experienced a long struggle from intuitively realizing the concept of "force" to obtaining a strict scientific definition of "force".

In the West, the concept of force was proposed before in physical science. First there was controversy in philosophy. Thales and others of the ancient Greek school of cosmology believe that nature is alive, and it is a living tissue that moves by itself like the human body. Under the guidance of this philosophical thought, there will be no origin of motion propositions and no concept of "force". Later Parmnides put forward the idea that motion does not exist from logical reasoning. His opponents proposed that the source of the movement is "force" to prove that the movement exists. This means acknowledging the original causal view that "force is cause and motion is effect".

Plato's concept of force is basically immaterial. He believes that the nature of movement is given to nature solely by an immortal living spirit. The final source of all forces in nature is the hidden world soul, which is the source of all physical activity. Of course, this metaphysical point of view is difficult to explain with motions like gravity.

In Aristotle's work, force is seen as being emitted from one object to another. This emitted force is not matter itself, but a "form" that exists depending on matter. According to this concept of force, its effects are limited to objects that touch each other; only by pushing or pulling can they interact with each other. This concept of force by Aristotle completely denied the existence of forces that acted through distance without touching each other. It can only be assumed that the planets are driving themselves; the stars themselves have life. But Aristotle first proposed the so-called "law of motion", which believed that the speed of a moving object was directly proportional to the resistance encountered when passing through the medium. However, he did not propose the unit of measurement for the quantities used, nor did he have a method for measuring these quantities. Aristotle believes that the weight of an object means "natural movement", which means that the object has a tendency to return to its natural position, rather than the reason for the forced movement of the object. This recognition ruled out the possibility of using weight as a unit of measurement.

Throughout the Middle Ages, the concept of force was deeply constrained by Aristotle's ideas, and little progress was made.

Galileo made important contributions to the establishment of classical mechanics, but did not form a complete concept of force. His definition of mass is ambiguous, so he cannot give a clear definition of force that applies to both statics and dynamics. Of course, he has a basic understanding of the principle of inertia. His principle of inertia states that an object can continuously move at a constant speed without being affected by external forces. He linked changes in force and speed. Breaking away Aristotle's long-term ideological restraint of linking force and speed. Newton opened the way by linking force and acceleration.

The concept of force occupies the most fundamental place in Newtonian mechanics. Newton proposed the definition of force in 1664 as the time variability of momentum (momentum equals mass times velocity). Newton's first law (law of inertia) is a qualitative definition of force, which gives the qualitative conditions under which a force exists and under what conditions. Newton's second law gives a quantitative definition of force, that is, the time rate of change of force equal to momentum; if the mass is constant, force is also equal to mass times acceleration. Newton's third law states that, for each force, there must be reaction forces of equal magnitude and opposite directions. It states that all forces are in pairs and can only be achieved when two objects interact (see Newton's laws of motion).

The amazing achievements of Newton's theory of universal gravitation extended the concept of super-forces to other branches of physics. However, Newton could not physically explain the essence of the distance action, so he was severely criticized by all parties for a long time. Einstein proposed the special theory of relativity in 1905, and pointed out that after the maximum speed of all physical effects was the speed of light, people realized that Newton's concept of super-range force had great limitations. Einstein clearly pointed out in his general theory of relativity in 1915 that the speed of gravity's propagation cannot be faster than the speed of light.

In history, many scientists and philosophers have pointed out that the concept of force in Newtonian mechanics is just a methodological

Definition : Force is generated by the interaction between an object (substance) and an object (substance). The magnitude, direction and action point of the force are the three elements of the force.

or

Materiality : Force is the effect of an object (substance, mass) on an object (substance, mass). When an object is subjected to a force, there must be another object exerting this effect on it. Force cannot exist without the object.

Mutuality (interaction force) : the action between any two objects is always mutual, and the force-applying object must also be stressed

Contains the three elements of force magnitude, direction and action point. Use one

unit

Newton (N)

When an object is subjected to several forces, if it remains stationary or moves in a straight line at a uniform speed, it is said that the object is subject to a balance force (or these forces are balanced). The stationary state and the state of uniform linear motion are also called equilibrium states. ^[1]

An object is subject to two forces, which maintain a stationary state or a state of linear motion at a constant speed. These two forces are a pair of balanced forces, called two-force equilibrium. In other words: "If an object remains stationary or moves at a constant speed in a straight line, the force it receives must be balanced (or unforced)."

Uniform rotation,

Strong interaction, weak interaction, electromagnetic force, universal gravity.

A branch of physics. It is used to study the laws of mechanical movement and balance of objects and their applications. Mechanics can be divided into three parts: statics, kinematics and dynamics. Statics mainly discusses the conditions under which an object maintains equilibrium under the action of external forces. Kinematics is a descriptive method of studying the mechanical motion of objects without considering the interaction between objects, and does not involve the causes of motion. Dynamics discusses the relationship between the forces on a particle system and the motion that occurs under pressure. Mechanics can also be divided into particle mechanics, rigid body mechanics and continuous medium mechanics according to the properties of the object under study. Continuous media are usually divided into solids and fluids. Solids include elastomers and plastics, while fluids include liquids and gases.

Between the 16th and 17th centuries, mechanics began to develop as an independent, systematic discipline. Galileo proposed the law of inertia through the study of projectiles and falling objects and used to explain the motion of objects and celestial bodies on the ground. At the end of the 17th century, Newton put forward three basic laws of mechanical motion, which made classical mechanics a systemic theory. According to Newton's three laws and the law of universal gravitation, the laws of the motion of falling bodies on the earth and the orbits of the planets were successfully explained. In the following two centuries, with the research and promotion of many scientists, it finally became a classic mechanics with perfect theory. In 1905, Einstein proposed the special theory of relativity. For high-speed moving objects, relative mechanics must be used instead of classical mechanics, because classical mechanics is just an approximate theory that the speed of an object is much smaller than the speed of light. In the 1920s, quantum mechanics was developed. It explained the microscopic phenomena that classical mechanics could not explain based on the duality of particles and waves of real particles and photons, and limited the scope of application of classical mechanics in the microscopic field. ^[4]

Classical mechanics of force

The basic laws of classical mechanics are Newton's laws of motion or other mechanical principles related to and equivalent to Newton's laws. They are mechanics before the 20th century. The measurement of the interval has nothing to do with the observer's movement, and the transfer of the interaction between the materials arrives instantaneously; the second is that all observable physical quantities can be measured indefinitely and accurately in principle. Since the 20th century, due to the development of physics, the limitations of classical mechanics have been exposed. As the first assumption, it is actually only suitable for low-speed motion compared with the speed of light. In the case of high-speed motion, time and length can no longer be considered independent of the observer's motion. The second assumption applies only to macroscopic objects. In microscopic systems, it is not possible in principle for all physical quantities to be accurately determined simultaneously. Therefore, the laws of classical mechanics are generally only approximate laws when macro objects move at low speed.

Newtonian mechanics

Newtonian mechanics was based on Newton's laws of motion and developed after the 17th century. The Newtonian mechanics is the study of the motion of the particle system directly based on Newton's law of motion. It takes the mass point as the object and focuses on the concept of force. When dealing with the problem of the mass point system, it is necessary to consider the force of each mass point separately, and then to infer the motion of the entire mass point system. Newtonian mechanics believes that mass and energy exist independently and are conserved. It is only applicable to the range where the speed of the object is much smaller than the speed of light. Newtonian mechanics mostly uses intuitive geometric methods, which is more convenient and simpler than analytical mechanics when solving simple mechanical problems.

Force Analysis Mechanics

Classical mechanics is divided into Newtonian mechanics and analytical mechanics according to the sequence of historical development stages and research methods. In 1788 Lagrange developed the work of Euler, Dallem and others, and published "Analytical Mechanics". In the analysis of mechanical problems, the entire mechanical system is taken as the object, and the general coordinate is used to describe the configuration of the entire mechanical system, focusing on the concept of energy. When the mechanical system is subject to ideal constraints, the motion of the system can be solved without considering the constraints. Analytical mechanics mostly uses abstract analysis methods, which shows its superiority in solving complex mechanical problems.

Force theory mechanics

It is a combination of mechanics and mathematics. Theoretical mechanics is an integral part of mathematical physics and the basis of various applied mechanics. It generally uses mathematical tools such as calculus, differential equations, and vector analysis to give an in-depth explanation of Newtonian mechanics and a systematic introduction to analytical mechanics. Because mathematics is applied more deeply in the field of mechanics, mechanics is more theoretical.

Kinematics

The purely analytical and geometric methods are used to describe the motion of the object, and the physical reasons for such motion of the object can be ignored. That is, the change of the relative position between objects over time is studied from the geometric aspect, without the cause of motion.

Force dynamics

Discuss the relationship between the force on the particle system and the motion that occurs under the force. Based on Newton's law, various basic principles of dynamics are proposed according to different needs, such as D'Alembert's principle, Lagrange's equation, Hamilton's principle, and regular equation. According to the current state of the system and the interaction between the internal parts and the interaction between the system and its surroundings, the movement that will occur can be predicted.

Force- elasticity

A discipline that studies the stress, deformation, and displacement of an elastic body due to external forces or temperature changes, so it is also called elastic theory. Elasticity is usually discussed about the linearity of an ideal elastomer. Its basic assumptions are: the object is continuous, uniform, and isotropic; the object is completely elastic; before the load is applied, there is no initial stress in the body; the deformation of the object is very small. Based on the above assumptions, the mathematical inference of the relationship between stress and deformation is often called mathematical elasticity. There is also the application of elasticity. If the deformation of the object is not very small, it can be studied by nonlinear elastic theory. If the internal stress of the object exceeds the elastic limit, the object will enter an incomplete elastic state. In this case, plasticity theory must be used to study.

Continuum mechanics

The motion of deformable objects with continuously distributed masses is studied, and the laws of mechanics that all continuous media generally follow are mainly discussed. For example, conservation of mass, theorem of momentum and angular momentum, conservation of energy, etc. Elastomer mechanics and fluid mechanics are sometimes referred to collectively as continuum mechanics.

Force relativity mechanics

It is based on relativity, which is very different from classical mechanics. It denies that space-time is absolute, and many effects cannot be explained by classical mechanics. For example: Mercury's perihelion precession, radar echo delay, etc., it also states that There is an inseparable relationship between energy and mass of matter (E = mc²).

Force submechanics

Fusion of matrix mechanics and wave dynamics. Quantum mechanics is based on Heisenberg's uncertainty principle and De Broglie's wave-particle duality. In quantum mechanics, the state of particles uses a wave function (R, t) indicates that it is a complex function of coordinates r and time t. Quantum mechanics tells us the probability (probability) density of a particle at a certain point in space. When the particle velocity is not large, the equation of motion satisfied by the particle is Schrödinger's equation. In the case of relativity with large particle velocity, Schrödinger's equation is replaced by Dirac's equation or Klein Gordon's equation. In quantum mechanics, the force between particles is described as the result of the exchange of bosons whose spins are integers, and Stephen Hawking opened a chapter in his book A Brief History of Time: Elementary Particles and Natural Force ". ^[5]