Force in Physics: What It Is, Definition, Concept and Types

Force in physics: what it is, definition, concept and types

In physics, a force is a vector magnitude that expresses an action that is printed on an object in a state of motion or rest. This action implies a change of speed, direction or shape. Its name comes from the Latin fortia.

According to the definition of force, it acts on an object that is capable of modifying its acceleration, that is, varying its speed and trajectory. A force can also cause an object to deform and a change in pressure.

In addition to its magnitude and direction, a force is determined by the point of application where it acts on a body.

If the sum of all the forces on a body is zero, then the center of mass is not accelerated. The body can deform under the influence of these forces. For example, the body can stretch due to two opposing forces.

Measurement Units

Force is measured in different units of measurement, with the newton (N) being the primary unit used in the International System of Units (SI). The newton is defined as the force required to provide an acceleration of 1 meter per second squared to an object of mass 1 kilogram.

In addition to the newton, there are other units of measure for force that are used in different contexts, some of which include:

  1. Pound-force (lbf): A unit of force commonly used in the United States and in countries that follow the imperial unit system. It is defined as the force required to accelerate a mass of one pound at 32.174 feet per second squared.

  2. Kilogram-force (kgf) or kilopond (kp): It is a unit used in some countries, especially in Asia. It is defined as the force exerted by gravity on an object with a mass of one kilogram.

  3. Dyne (dyn): It is a unit of force in the CGS (centimeter-gram-second) system. One dyne is the force required to accelerate one gram at one centimeter per second squared.

Newton's Laws: the Relationship Between Force, Mass and Acceleration

Newton's laws are three fundamental laws of classical mechanics that describe how forces affect the motion of objects. Through Newton's laws the concepts of force, mass and acceleration are related.

  1. Newton's First Law (Law of Inertia): This law states that an object at rest tends to remain at rest, and an object in motion tends to maintain its uniform rectilinear motion, unless an external force acts on it. In other words, an object will not change its state of motion unless a net force acts on it.

  2. Newton's Second Law (Law of Force and Acceleration): This law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.

  3. Newton's Third Law (Law of Action and Reaction): This law states that for every action, there is a reaction of equal magnitude but in the opposite direction. That is, when object A exerts a force on object B, object B exerts a force of equal magnitude but in the opposite direction on object A. 

Types of Forces

There are several types of forces in physics. Here are some of the main types that are considered in physics:

  1. Gravitational force: It is the force of mutual attraction that exists between two objects with mass. The force of gravity is responsible for objects falling towards Earth and for the orbit of planets around the Sun.

  2. Electromagnetic force: It is the force that acts between electrically charged particles. This force is responsible for the interaction between electrons and protons in atoms, as well as for electromagnetic phenomena such as magnetism and electricity.

  3. Strong Nuclear Force: It is an extremely powerful force that acts within the atomic nucleus. This force is responsible for holding the protons and neutrons together in the nucleus, counteracting the repulsive electromagnetic force between the positively charged protons.

  4. Weak Nuclear Force: It is a force responsible for certain types of radioactive decay. It is associated with the interactions between subatomic particles and is involved in processes such as beta decay.

  5. Friction force: It is the one that opposes the relative movement of two surfaces in contact. Friction can be static (when objects are not moving), kinetic (when objects are moving), or fluid (when an object moves through a fluid, such as air or water).

  6. Elastic Force: Occurs when an elastic object, such as a spring, is stretched or compressed. This force is proportional to the deformation and is directed in the opposite direction to the displacement.

  7. Tension force: this is an internal force that acts within an object when it is being subjected to stretching or traction. This force spreads along the object, maintaining its structural integrity and resisting shape change due to external forces that stretch it.

Relation to Work

The application of a force can involve obtaining work: work is defined as the transfer of energy caused by the application of a force over a distance.

Mathematically, work (W) is calculated by multiplying the magnitude of the force (F) by the distance traveled in the direction of the force (d), and then multiplying it by the cosine of the angle (θ) between the force and the direction of the force. displacement. This is expressed as:

W = F * d * cos(θ)

Work can be positive, negative, or zero, depending on the relationship between force and displacement.

Free Body Diagrams

Free body diagrams are tools used in physics to analyze and visualize the forces acting on a particular object. These diagrams represent an isolated object, showing all the forces acting on it and their relative direction.

This diagram allows you to clearly visualize the forces and analyze their influence on the movement or balance of the object. In addition, they are useful in various branches of physics, such as mechanics, to analyze the movement of objects, the equilibrium of systems and the resolution of force problems.


Published: November 29, 2021
Last review: July 6, 2023