# Forces – all about it

## Basic mechanics

In physics we often stumble over the concept of force. But what exactly is a force and in which subject areas do we actually use it? Before we take a closer look at the term force, let us first clarify the question in which areas of mechanics it plays a role.

As we already know from the Mechanics chapter, classical mechanics generally deals with bodies at rest and in motion and the forces that occur as a result. Two major sub-areas can be distinguished: the kinematics and the dynamics.

Figure 1: Mechanics classification

In kinematics, the study of movements, mechanical movements are considered without considering the acting forces. An example of this would be a uniform motion of a body where the cause of the motion is irrelevant. The second major topic is the dynamics. In this sub-area, attacking forces are also taken into account, which is why the dynamics are also called doctrine of forces is titled. This can be further subdivided into the sub-area of staticsin which forces on bodies at rest are treated and in the subfield of kinetics, in which forces are examined as the cause of the movements. When it comes to forces, we are in mechanics in the sub-area of ​​dynamics.

## Powers – what is it all about?

Forces accompany us every day in everyday life. We encounter forces both when just standing on the ground and when throwing a ball. But what exactly is a force in physical terms?

### description of a force

Physically, a force is cause for having a body his state of motion of stillness or of uniform movements changes or one deformation of the body takes place.

A force can usually only be visually identified by its Effect recognize. This definition of a force goes back to the well-known scientist Isaac Newton (1643 – 1727). Correspondingly, in literature, the power is associated with the letter f and the associated unit Newton marked after their inventor.

Expressed in words, this means that 1 Newton is the force required to accelerate a mass of 1 kg at 1 m/s².

A force is often measured by a so-called spring dynamometer. This has a spring inside which, depending on the size of the pulling force, is pulled apart. With the help of a suitable scale, the acting force can be read off directly.

From a physical point of view, however, not only a numerical value and its associated unit are necessary for the description of the force.

A full description of the force is characterized by:

• Amount (numerical value with unit)
• line of action
• sense of direction
• attackpoint

To illustrate these different components, they are drawn in the graphic below. First, we start with a certain starting point or attackpoint. From there the line of action of the force are transferred to the sketch, i.e. along which line the force actually acts on the body. How big is the power (the amount), is determined by drawing an arrowlength Are defined. Finally the sense of direction added in the form of an arrowhead. In this way we get a force arrow with a certain length and a certain direction.

Figure 2: Components of a force

Mathematically, therefore, the force is marked with an arrow above the letter F. So this as directed Size defined as you could just see in the example. However, in the literature, the amount is often only used if it is permissible for the task.

### Newton’s axioms

In this context, Isaac Newton, in addition to describing a force, also formulated various principles relating to forces. The so-called Newton’s axioms or Newtonian principles form an important foundation in the mechanics. In the literature, three different Newton’s laws are mainly mentioned, which we will briefly discuss below.

#### 1. Newton’s axiom («lex prima»)

Newton’s first axiom, too law of inertia or. axiom of inertia, goes back to the definition of force. It states that the state of motion of a body not changedas long as no external acting forces cause a change of state.

The body remains i.e. in its state of rest or uniform motion, as long as it is not forced to change this by external forces.

#### 2. Newton’s axiom («lex secunda»)

That principle of actionalso known as Newton’s second law or Newton’s lawalso goes back to the definition of force and establishes the connection between physical quantities. The unit results in a relationship between the quantities mass, acceleration and force.

The relationship between the quantities of force, mass m and acceleration is defined by:

However, the second principle is valid in this form only if the mass of the body constant remains. Due to the derivation via the impulse, movements of bodies with variable mass to be viewed as.

#### 3. Newton’s axiom («lex tertia»)

The 3rd Newton’s law, the so-called interaction law or reaction principle states that forces always occur in pairs.

Every force (actio) generates an equal reaction (reactio) or in short:

actio = reactio

When body A exerts a force on body B, body B exerts an equal but opposite force on body A. This is not to be confused with the balance of power, which we will discuss later in the article.

#### Superposition principle (4th Newton’s law «lex quarta»)

Because of superposition principle Is it at all possible to add several acting forces to a resulting force.

If two or more forces act on a body, they can be combined to form a sum.

More information on the basics of force and the associated Newton’s axioms can be found in the chapter on force and the associated sub-chapters of Newton’s laws.

### effect of forces

As already mentioned, mechanical forces cannot be recognized directly, but based on their effect. Physically, different effects of forces can be distinguished:

Figure 3: Effect of forces

A force can lead to a change in motion or a change in shape of a body. The speed can be changed by the object accelerated or is slowed down. In addition, the Direction of the movement are reversed by acting forces. Temporary deformations, in which the body springs back to its original state after the applied force is removed, are called elastic designated. In contrast, there is plastic Deformation. The body is permanently deformed by the force acting on it and remains in this shape even after the forces have been removed.

This plays an important role, especially in impact processes. The terms mechanical work, mechanical energy and mechanical power are therefore also closely related to force.

We already know what exactly a force is, how it can be described and what effects it can trigger. But what forces are there anyway?

## division of forces

There are different forms of forces in physics. Basically, they can be divided into two areas: fundamental forces and derived forces.

### fundamental forces

The fundamental forces represent the cornerstone for all existing forces. Based on four basic forces, which correspond to the fundamental interactions of nature, all other forces can be traced back to these forces.

Figure 4: Overview of fundamental forces

#### gravity

Gravity or gravity acts as attraction between two crowds and works over very long distances. The best-known example of this is gravity. It ensures that all bodies on earth and the earth attract each other. This is how it is possible to walk on the surface of the earth instead of floating around. She owns one infinite range and also cannot be shielded. It is still the weakest of all four fundamental basic forces, which is why we can, for example, pick up a stone from the ground relatively easily. In the literature, the gravitons are often mentioned as exchange particles, which ensure that the gravitation is transferred.

#### gravity

Gravity or gravity acts as attraction between two crowds and works over very long distances. The best-known example of this is gravity. It ensures that all bodies on earth and the earth attract each other. This is how it is possible to walk on the surface of the earth instead of floating around. She owns one infinite range and also cannot be shielded. It is still the weakest of all four fundamental basic forces, which is why we can, for example, pick up a stone from the ground relatively easily. In the literature, the gravitons are often mentioned as exchange particles, which ensure that the gravitation is transferred.

#### electromagnetic force

Also up great distances the electromagnetic force acts. In contrast to gravity, however, this can be shielded. Electromagnetism is composed of electrical and magnetic phenomena. Between electric loaded particle of different or the same charge there are force effects. It causes an attraction for two oppositely charged particles such as an electron and a proton. Conversely, particles with the same charges repel each other. Moving charges also create a magnetic field. For example, the electromagnetic force ensures that atoms are held together with their positive atomic nucleus and the negatively charged electrons in the shell. The electromagnetic interaction is transmitted by photons. A classic example of this is light. The electromagnetic force is the second weakest of the four fundamental forces, but is quite a bit stronger than gravity.

#### Strong power

As the name suggests, the strong power is the strongest of the basic powers. In this case, the exchange particles are the so-called gluons. This strong force is found in the atomic nuclei, which consist of protons and neutrons. Normally, protons repel each other due to their electrical charge. The strong force indirectly ensures that the protons and neutrons are bound in the atomic nucleus and that this remains a stable nucleus….