Study Material

Forces at a distance

What are remote forces?

The forces at a distance or forces of action at a distance, as they are also known, are those that do not need the objects with which they interact to be in physical contact. From there it derives its name.

Among the remote forces, the magnetic force stands out
Among the remote forces, the magnetic force stands out

The weight is the force away most famous and familiar of all because it acts on every imaginable everyday situation, but also the electric and magnetic forces.

For example, an apple will fall from the tree because it is near the surface of the Earth and the Earth always exerts an attractive force on it, whether it is suspended from the tree at a certain height, it is on a table or it is simply on soil. The weight of the apple always acts and causes the apple to fall as soon as the opportunity presents itself.

In this, distance forces differ from contact forces, because they do require contact between surfaces to manifest their action. Friction is one of the most frequent contact forces and there is no problem in which contact forces act together with distance forces on the same body.

Weight is the main known force at a distance, or at least the one most familiar to all, but there are others, such as the electrostatic force, the magnetic force, and the strong and weak nuclear forces, that act at the level of the atom and the atomic nucleus.

Characteristics of remote forces

The main characteristics of remote forces are:

-They do not require that the interacting objects be in direct contact.

-They have an associated force field that serves as a mediator for the interaction.

Isaac Newton had no problem establishing action at a distance as the way gravity acts on the falling apple. Although Newton was thinking specifically about gravity, and not about electrical interaction or magnetic interaction that do not require contact between bodies.

However, there is little downside to this, since action at a distance implies that information between objects flows instantaneously. Thus, the body that exerts the force always detects the position of the other object at all times, but the point is that no information can travel faster than light in a vacuum.

The concept of force field

The fact that nothing travels faster than light in a vacuum led to the creation of the concept of force field , through which interaction occurs.

The English physicist Michael Faraday was the first to define a force field, this time thinking about electromagnetic interaction, although the idea is extended to other forces that act without the need for direct contact.

Thus, for example, the Earth’s gravitational field is the one that acts as a mediator between the Earth and the apple, and it is through the field that the latter perceives the mass of the Earth and is attracted to it.

That is why some authors prefer to call distance forces as field forces ( field force in English), the field being a vector entity related to the force and in charge of establishing the interaction between objects at each point in space. Thanks to the force field, the object that produces it has no need to even know that it is affecting another.

Examples of forces at a distance

The forces briefly described below are part of the fundamental interactions of nature. The most familiar, as stated, are gravity and electromagnetic forces.

However, the role of the strong and weak nuclear forces is fundamental in the stability of matter , without them the universe as we know it would not exist.

The gravity

The force of gravity is the most familiar remote force of all, as it manifests itself through weight.
The force of gravity is the most familiar remote force of all, as it manifests itself through weight.

The force of gravity arises between two objects that have mass and is always attractive. It is called weight, when the object that exerts it is the Earth and the one that receives it is close to the surface, but it exists between any pair of objects with mass, although if the mass of the objects is very small, the force of attraction between both are not obvious.

It is long-range, that is why the force of gravity manifests itself powerfully on a cosmic scale: thanks to it the Sun keeps the planets and other objects of the Solar System in their respective orbits.

It is also the primordial force thanks to which celestial bodies such as stars and planets, including the Sun and Earth, are formed.

Electrostatic force

This force makes its appearance between objects that have an electrical charge and can be attractive or repulsive. There are two types of charge: positive and negative. In the atom, the protons in the nucleus have a positive charge, while the electrons have a negative charge.

In general, the atom is neutral, which means that the number of protons equals that of electrons, but sometimes matter is ionized, that is, it acquires excess electrons or loses them. In such a case there is a net charge, which can interact with other charges.

The existence of the electrostatic force is easy to check: just comb your hair with a plastic comb and bring it close to pieces of paper or confetti. You can immediately see that the comb attracts the pieces of paper.

Magnetic force

Direction of magnetic force in magnets illustrated with their magnetic poles
Direction of magnetic force in magnets illustrated with their magnetic poles

The ancient Greeks knew, through the testimony of Thales of Miletus, an abundant mineral in the hills of the city of Magnesia in Asia Minor, capable of attracting pieces of minerals based on iron or nickel. This mineral is an iron oxide called magnetite , which in turn can magnetize other susceptible minerals and transform them into a magnet.

Magnets deflect the compass and also a wire through which an electric current circulates behaves like a magnet. In fact, magnetism is associated with moving electrical charges.

Polarity is a characteristic of magnets, there are two types: north pole and south pole. Opposite poles attract and like poles repel, but unlike electric charges, in nature they are never separated, magnets are always dipoles.

The strong and weak nuclear forces

Illustration of an atom with its electrons, nucleus, neutrons and protons, where nuclear forces occur
Illustration of an atom with its electrons, nucleus, neutrons and protons, where nuclear forces occur

These forces are not easily observable, but they have the important mission of keeping the atomic nucleus cohesive, very necessary if it is considered that the nucleus is made up of protons, which, since they are all positively charged, experience electrical repulsion.

They are short-range forces, since they only act at distances similar to the size of the atomic nucleus, approximately on the order of 10-15 m, an extremely small distance.

All forces at a distance are very important, because in their action they combine to shape the known universe.

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