Force is the physical phenomenon that describes the speed of displacement of a body or object, taking into account the direction and intensity of said movement. I
n order for us to measure force, there must be an interaction between two objects or bodies. In physics , force is represented by the letter F and, according to the International System, it is measured in Newtons (N).
In this article, we shall touch the basic concept behind what are forces, and, what are the different types of forces with examples! Let’s dive in!!!
Definition of Force in Physics:
“A force is a quantity capable of modifying the amount of movement or the given shape 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 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 that affects a body is responsible for the changes in its state of motion, such as its rectilinear trajectory and its 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.
Normally we talk about force in our daily lives, without necessarily using this word as physics does . The 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.
On the other hand, in Newtonian (or classical) mechanics, there are many other identifiable forces, such as the friction force, the gravitational force , the centripetal force, etc.
A force can be thought of as a physical entity that describes the intensity of the interactions between objects , closely related to energy .
Is force a scalar or vector quantity?
For classical mechanics, every force 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.
Different Types of forces in physics:
In physics, there are different types of force that can be calculated using different formulas.
Next, we present a list with important types of force in physics.
Difference Between Contact And Noncontact Forces Examples
- Force according to Newton’s second law.
- friction force.
- Normal strength.
- Centripetal force.
- elastic force.
- tensile strength.
Field Forces or Non-contact forces:
- Gravitational force.
- electric force.
- electromagnetic force.
Force according to Newton’s second law
Newton’s Second Law states that if a force is applied to a body, it experiences acceleration. In other words, to move an object it is necessary to apply a certain amount of force. In addition, the required force will also depend on the mass of the body. The more mass the body has, the greater the force needed to move it.
According to this law, the formula to calculate the force is:
Next we explain the meaning of each term of the formula, together with the units in the International System
- F : corresponds to the force, expressed in Newtons, N . This unit is equivalent to (kg xm) / s 2 .
- m : is the mass of the moving body, expressed in kilograms, kg .
- a : is the acceleration of the body, expressed in meters per second squared, m / s 2 .
This formula is key to calculating how much force we need to apply to an object to pull or push it.
The force of friction is that which resists the sliding or rolling of a solid object on a surface.
If the force of friction on the surface is greater than the force applied by the object, the object will remain at rest. This is called static friction. Conversely, if the object overcomes the force of friction and moves or rolls on the surface, this is called kinetic friction.
Both in static and kinetic friction, the formula that is applied is the following:
- F : is the friction force expressed in Newtons, N . This force can be static or kinetic friction.
- µ : is the coefficient of friction of the surface. The coefficient changes depending on whether it is static or kinetic friction, and depending on the characteristics of the surface material. It has no units.
- N : is the normal force, also expressed in Newtons, N .
The normal force is that which opposes the weight of an object resting on a surface. Therefore, the normal force is related to the force of gravity. The normal force can be calculated with the following formula:
- N : is the normal force expressed in Newtons, N .
- m : is the mass of the body that rests on the surface, expressed in kilograms, kg .
- g : is the acceleration of the body due to the terrestrial gravitational force, with a value of 9,776 m/s 2 .
The normal force is also applied to an object resting on an inclined surface. In this case, the formula is:
In which θ is the angle of the inclination of the surface with respect to the perpendicular of the earth plane, without units.
Centripetal force is the force acting on an object moving around an axis of rotation. The force is always directed towards the axis of rotation, thus being a force that keeps the object circulating around the axis. Due to this movement, the object suffers an effect of inertia in the opposite direction (centrifugation).
To illustrate this type of force, let’s take the Earth and the sun as an example. The force of gravity is the centripetal force that keeps the Earth revolving around the sun. On the other hand, due to the inertia of the movement, the Earth tends to move away from the sun. Together, the centripetal force and the effect of inertia prevent Earth from slipping out of orbit or colliding with the sun.
The centripetal force is calculated with the following formula:
- F : is the centripetal force applied on the object that rotates around the axis of rotation. It is expressed in Newtons, N .
- m : is the mass of the moving object, expressed in kilograms, kg .
- v : is the speed of the moving object, expressed in meters per second, m/s .
- r : is the distance between the object and the axis of rotation, expressed in meters, m .
If one knows the angular velocity, the formula can be rewritten as follows:
In which w is the angular velocity, expressed in 1/s .
The elastic force is that which returns a body to its original shape after being deformed by an external force. Let’s imagine that we take a spring and extend it with our hands, deforming it. When released, the elastic force of the spring allows it to return to its original shape.
According to Hooke’s Law, the elastic force can be calculated with the following formula:
- F : is the elastic force applied to the object, expressed in Newtons, N .
- k : is the constant of proportionality that depends on the shape and composition of the object. It is expressed in Newtons per square meter, N / m 2 .
- ΔL : is the amount of deformation produced by the external force, expressed in meters, m . The term ΔL is interchangeable with x .
Tension force is a tensile force transmitted by a rope, thread, cable, or chain on an object. It is a force that opposes another, such as gravity or a person pulling on a rope.
Tension force does not have a predefined formula. Instead, the opposite force should be taken as a reference. For example, if we want to calculate the force of tension in a string that supports a sphere, the force of tension will be the same as the gravitational force applied to the object. That is to say:
The gravitational or gravitational force is a force at a distance and of attraction between bodies that contain mass. The magnitude of this force increases or decreases in proportion to the mass of the bodies, as long as they are within the gravitational field. Added to this, the gravitational force is inversely proportional to the square of the distance between the bodies.
This force can be calculated using the following formula:
- F : is the gravitational force, expressed in Newtons, N .
- G : is the gravitational constant, with an approximate value of 6.674 x 10 -11 m 3 / (kg xs 2 ) .
- m 1 and m 2 : are the masses of the bodies that interact with each other, expressed in kilograms, kg .
- r : is the distance between the centers of mass of both bodies, expressed in meters, m .
To calculate the gravitational force that the Earth exerts on a body, we can simplify the formula as follows:
- F : is the gravitational force exerted on the body, expressed in Newtons, N .
- m : is the mass of the body within the gravitational field of the Earth, expressed in kilograms, kg .
- g : is the acceleration of the body towards the center of the Earth, with an approximate value of 9,807 m/s 2 .
The electric force is the force of attraction or repulsion between two electric charges. These charges will attract or repel depending on the type of charge. If they are both positive or negative charges, they will repel each other; on the other hand, if they are different charges, they will attract each other. For example, two protons or electrons will repel each other, while a proton and an electron will attract each other.
Coulomb’s Law defines the electric force by the following formula:
- F : is the electrical force, expressed in Newtons, N . It can be a force of attraction or repulsion.
- k : is the coulomb constant or electrical constant of proportionality. It has an approximate value of 8.987 x 10 9 (N xm 2 ) / C 2 .
- q1 and q2 : is the value of the electric charges, expressed in coulombs, C .
- r : is the distance that separates the electric charges, expressed in meters, m .
If we take the formula into account, the electric force will be greater as the values of the electric charges are higher and the distance between them is less.
The electromagnetic force occurs when electrically charged particles are in motion. Specifically, it is the force that the electric and magnetic field that a charge applies to another that is in motion.
According to the Lorentz force law, the electromagnetic force is described as:
This equation contains two parts: one related to the electric field, and the other to the magnetic field.
The formula that describes the force applied by the electric field is:
- F : is the electric force applied by the electric field on a charge, expressed in Newtons, N .
- q : is the charge that moves in the electric field, expressed in coulombs, C .
- E : is the electric field, expressed in Newtons per coulombs, N/C .
The formula that describes the force applied by the magnetic field is:
- F : is the magnetic force applied by the magnetic field on a charge, expressed in Newtons, N .
- q : is the charge that moves in the magnetic field, expressed in coulombs, C .
- v : is the velocity of the charge, expressed in meters per second, m/s .
- B : is the magnetic field, expressed in teslas, T . This unit is equivalent to (N xs) / (C xm) .
- θ : is the angle between the velocity of the charge and the magnetic field. It has no units.
What are the Inter-molecular forces?
They are those that keep the molecules together , forming more complex structures and 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
- Hydrogen Bonds.
Relationship between force and energy:
Although the concepts of energy and force can be related, they do not mean the same thing. Energy is present in all bodies and objects, depending on whether they are at rest or in motion, potential energy and kinetic energy, respectively.
The precise force of the interaction of two bodies and, depending on the force applied from one object to another, we can transform potential energy into kinetic energy. The force exerted between these objects is called work .