Force

We explain what a force is for physics, its characteristics and its types according to each theory. Also, how it is measured and various examples.

What is a force?

In technical terms, a force It is a quantity capable of modifying the quantity of movement or the shape given of a body or a particle. It should not be confused with the concepts of effort or energy.

Commonly, the concept of force is explained in the terms of classical mechanics established by the principles of Isaac Newton (1642-1727), known as the Laws of Motion and published in 1687 in his Principia Mathematica.

According to classical mechanics, the force incident on a body is responsible for changes in its state of motion, such as its rectilinear path and uniform displacement, and for giving it an acceleration (or deceleration). Furthermore, every force acting on a body generates an identical force, but in the opposite direction.

We normally talk about force in our daily lives, without necessarily using this word as physics does. Force is studied by physics and according to it Four fundamental forces are recognized at the quantum level: the gravitational force, the electromagnetic force, the strong nuclear force and the weak nuclear force.

Instead, In Newtonian (or classical) mechanics, there are many other forces identifiable, such as friction force, gravitational force, centripetal force, etc.

See also: Power in physics

Strength characteristics

a force can be thought of as a physical entity that describes the intensity of interactions between objects closely related to energy.

For classical mechanics, every force It is composed of a magnitude and a direction which is why it is denoted by a vector. This means that it is a vector quantity, not a scalar one.

Types of force

There are several types of force, depending on their nature and focus:

According to Newtonian mechanics:

• Friction force It is the force that opposes the change in the movement of bodies, exerting a resistance to leaving the state of rest, or movement, as we can perceive when starting a heavy object by pushing it.
• Gravitational force It is the force that the mass of bodies exerts on nearby objects, attracting them towards itself. This force becomes notable when all or some of the interacting objects are very massive. The example par excellence is the planet Earth and the objects and beings that live on its surface; There is a gravitational force of attraction between them.
• Electromagnetic force It is the attractive and repulsive force that is generated by the interaction of electromagnetic fields.

You can also talk about:

• Contact force It is the force exerted from direct physical contact between one body and another.
• Force at a distance It is the force that can be exerted without any physical contact between bodies.

According to relativistic or Einsteinian mechanics:

• Gravitational force It is the force that appears to exist when massive objects curve space-time around them, forcing smaller objects to deviate their trajectories and approach them.
• Electromagnetic force It is the force exerted by electromagnetic fields on charged particles of matter, following the expression of the Lorenz force.

According to quantum mechanics:

• Gravitational force It is the force that one mass exerts on the other, being a weak force, in only one direction (attractive), but effective over long distances.
• Electromagnetic force It is the force that affects electrically charged particles and the electromagnetic fields they generate, being the force that allows molecular union. It is stronger than gravity and has two senses (attraction-repulsion).
• Strong nuclear force It is the force that keeps the nuclei of atoms stable, keeping neutrons and protons together. It is more intense than electromagnetic, but has a much shorter range.
• Weak nuclear force It is the force responsible for radioactive disintegration, capable of executing changes in subatomic matter, with an even smaller range than strong nuclear forces.

Force units

According to the International System, the force It is measured in units called Newtons (N) in honor of the great British physicist. These units correspond to 100,000 dynes and are understood as the amount of force applied during one second to a mass of one kilogram, so that it acquires the speed of one meter per second. That is, that:

1 N = (1kg x 1m) / 1 s²

There are other units for other metric systems, which are equivalent, in Newtons, to:

• 1 kilogram-force or kilopond is equal to 9.81 N
• 1 pound-force is equal to 4.448222 N

How is strength measured?

The dynamometer is the ideal device for measuring force. It is also used to calculate the weight of objects. It was invented by Isaac Newton himself, using the stretching of a spring and Hooke's Law of Elasticity, in a similar way to a spring balance.

Modern versions of the dynamometer follow the same principle and have hooks or rings at the ends of their cylindrical body, inside which there is a spring or spiral that acts as a spring. At one end the force measurement will be marked (in some cases it may even appear on a digital screen).

Examples of force

There are constantly examples of strength around us. When exerting our muscular force on an object to lift it We are overcoming the force of gravity. If we push a massive body with our shoulder like a refrigerator, we will not only have to overcome gravity, but also the force of friction that opposes movement.

The same thing happens when we stick a refrigerator magnet since the magnetic force holds it in place, but if we approach it to another magnet by the same pole, however, we will notice a faint repulsive force, which is another character of the same magnetic force.

Force and movement

Force and motion are strongly involved with each other. First of all, because force is something capable of starting, stopping or modifying a movement.

For example, when a baseball hits the bat, the batter's force is imposed on the second to deflect its trajectory (the same as the pitcher's force initially exerted on it, since the ball is normally at rest) and throw it far into the field.

Whenever there is a force on a body in the same direction as the displacement, there will be work done by that force. The work necessary for this movement to occur is equal to the energy necessary to move the body. Depending on the type of force and the type of movement, various mathematical formulas will be available to calculate them.

Continue in: Movement

gravity force

The force of gravity It is that attractive force that masses exert on the matter around them with an intensity proportional to their mass and inversely proportional to the distance that separates them.

In fact, the Sun attracts our planet from a distance, with the same kind of force with which it attracts us, who live on its surface. Gravity can be overcome momentarily, as we do when jumping, but we will eventually succumb to it. Everything that rises freely, must fall.

Intermolecular forces

are those that keep molecules together forming more complex structures with greater mass, depending directly on the nature of the atoms involved. That is why they are also known as intermolecular bonds or atomic bonds. These forces can be of two types: Van der Waals Forces or Hydrogen Bonds.

Continue with: Dynamics

References

• “Strength” on Wikipedia.
• “Force” in the Department of Education, University and Vocational Training of the Xunta de Galicia.
• “Forces in dynamic systems” in Andalusian Society of Mathematical Education «Thales».
• “Force” in Force and Pressure Metrology Management of Mexico.
• “Forces and Motion” in PHET Interactive Simulations at the University of Colorado Boulder.
• “Force (physics)” in The Encyclopaedia Britannica.