We explain what a force is, its units and how this magnitude is classified. Also, its general characteristics, properties and more.
What is force?
Force is any agent with the ability to modify the amount of movement or the shape of materials . What measures force, as a vector magnitude, is the intensity of the interactions between two particles or systems of particles.
It is distinguished from the concepts of work (which exists when a force acts on a body generating its displacement) and energy (which is a measure of the capacity of a particle or body to generate work).
Isaac Newton invented the first instrument to measure forces, called a dynamometer . Since weight is a form of force, it is also used to weigh objects.
There are different ways of measuring force, depending on the various systems:
- International System of Units . In this system, mass is measured in kilograms and acceleration in meters over seconds squared. Thus, force is measured in Newtons (N), one Newton being equal to one kilogram per meter over seconds squared (kg.m / s 2 ).
- Technical System . This system measures force according to technical units of mass (utm), without depending on other magnitudes. That is why it is a fundamental unit. The measure of force in this system is the kilogram-force (kgf).
- Cegesimal System of Units . Its measure of force is the dina (dyn).
- Anglo-Saxon system of units . Its measure of force is the pound force (lbf).
Types of force
Among the various types of force, the main ones are:
- Gravitational force . It is the force of attraction between two bodies. It depends on the distance between the two and their masses.
- Electromagnetic force . It affects bodies that are electrically charged. Between the bodies charged with opposite charges there is a force that attracts them, while between the bodies charged with equal charges there is a force that repels them. The electromagnetic force intervenes in physical and chemical transformations of atoms and molecules .
- Strong nuclear force . It holds together the components of atomic nuclei: neutrons and protons.
- Weak nuclear force . It is responsible, among other things, for the beta decays of the atomic nucleus.
- Static friction force . It is the resistance that a body offers to be moved, it is equal (but in the opposite direction) to the minimum force necessary to move it.
- Elastic force . It is the ability of certain objects to regain their original shape when deformed. For example, springs. The elastic force depends on certain physical properties of objects.
- Friction force . When one object moves over another, the resistance that the second offers to the movement of the first is called the friction force.
- Normal force . It is the force that the surface on which a body rests exerts on it. Its direction is perpendicular to the surface.
- Thrust force . The fluids ( liquids or gases ) exert a biasing force to the body that are embedded in them. This force has a vertical direction and an upward direction.
Properties of force
Because it is a vector magnitude, every force has four properties:
- Intensity . It is the amount of force exerted.
- Address . All force is exerted in space, with some angle or inclination with respect to a reference system.
- Sense . When two objects exert forces on each other, the direction of both forces can be the same, but their direction is opposite (for example, one force is exerted from top to bottom while the other force is exerted from bottom to top).
- Application point . It is the surface or point where the force is applied.
There is a system of forces when several forces act at the same time on the same body . From the interaction of each of these forces (components), a single force is called the Resulting Force. These systems can be of:
- Collinear forces . The forces are applied on the same line, that is, they have the same direction, but they may or may not have the same direction.
- Parallel forces . The forces are not applied on the same line but on parallel lines. If they have the same sense, the resulting force will be the sum of all of them. If they have the opposite sense, they should be subtracted.
- Angular congruents . The forces have different directions but intersect at one point.
Distance and contact force
The forces that bodies exert on each other are distinguished in:
- Contact forces . They are all the forces that are exerted through contact between two objects. For example, the force of friction.
- Forces at a distance . They are those that are exercised even when the objects are distanced from each other. For example, the gravitational force and the electromagnetic force.
Linear moment of force
Force measures the intensity of interactions between two particles or systems of particles and is calculated as the mass of a body times its acceleration. Momentum is the product of mass and velocity. It is also called momentum.
Static and dynamic effects of force
The effects of a force can be:
- Static effects . They occur when a force deforms bodies.
- Dynamic effects . They occur when a force modifies the speed of a body.
Effects of force on different body types
Each object has physical characteristics that make it react in different ways to certain forces:
- Elastic bodies . They deform when a force is applied to them, but they return to their initial state when it is stopped.
- Plastic bodies . They deform when a force is applied to them and cannot recover their initial state.
- Solid body . They are not deformed or modified by applied forces, unless the force is strong enough to break them.
The interactions between these various objects depend on the properties (intensity, direction, direction and point of application) of the couple of forces involved. For example, a rubber ball (elastic) that hits a wall (solid) is momentarily deformed the instant it hits the wall and then the reaction force of the wall on the ball will change its direction.
Duration of force
Depending on the duration of the application of forces, they are classified into:
- Instantaneous forces . They act for a brief moment and, therefore, cause uniform movements.
- Constant forces . They act continuously on bodies, that is why bodies are continually accelerated while force is applied. An example is the force of gravity .
Exteriority or interiority of force
Although we are mainly talking about the forces that one body exerts on another (external force), there are also internal forces in bodies. Atomic forces, for example, are internal forces of an object .
On the other hand, if we consider two bodies as a physical system, for example, the forces that one exerts on the other will be internal to the system.
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