The word "power" is so comprehensive that to give it a clear concept - the task is almost impossible. The variety from muscle power to the power of the mind does not cover the entire spectrum of concepts embedded in it. The force, considered as a physical quantity, has a clearly defined meaning and definition. The force formula defines a mathematical model: the dependence of force on the main parameters.
The history of the study of forces includes the determination of dependence on parameters and experimental evidence of dependence.
Strength in Physics
Strength is a measure of the interaction of bodies. The mutual action of bodies on each other fully describes the processes associated with a change in speed or deformation of bodies.
As a physical quantity, force has a unit of measure (in the SI - Newton system) and a device for measuring it is a dynamometer. The principle of action of the dynamometer is based on a comparison of the force acting on the body with the elastic force of the dynamometer spring.
For a force of 1 Newton, the force is taken, under the influence of which a body weighing 1 kg changes its speed by 1 m in 1 second.
Strength as a vector quantity is determined by:
- direction of action;
- point of application;
- module, absolute value.
When describing the interaction, these parameters must be indicated.
Types of natural interactions: gravitational, electromagnetic, strong, weak. Gravitational forces ( gravity with its variety - gravity) exist due to the influence of gravitational fields surrounding any body with mass. The study of gravitational fields has not been completed so far. It is not yet possible to find the source of the field.
A large number of forces arise due to the electromagnetic interaction of the atoms of which the substance consists.
Pressure force
When the body interacts with the Earth, it exerts pressure on the surface. The pressure force , the formula of which is of the form: P = mg, is determined by body weight (m). The acceleration of gravity (g) has different meanings at different latitudes of the Earth.
The force of vertical pressure is equal in magnitude and opposite in direction to the elastic force arising in the support. The formula of force in this case varies depending on the movement of the body.
Body weight change
The action of the body on the support due to interaction with the Earth is often called the weight of the body. Interestingly, the value of body weight depends on the acceleration of movement in the vertical direction. In the case when the direction of acceleration is opposite to the acceleration of gravity, an increase in weight is observed. If the acceleration of the body coincides with the direction of gravity, then the weight of the body decreases. For example, being in a rising elevator, at the beginning of an ascent, a person feels an increase in weight for some time. It is not necessary to say that its mass is changing. At the same time, we divide the concepts of “body weight” and its “weight”.
Elastic force
When the shape of the body (its deformation) changes, a force appears that seeks to return the body to its original shape. This force was given the name "elastic force". It arises due to the electrical interaction of the particles that make up the body.
Consider the simplest deformation: tension and compression. Stretching is accompanied by an increase in the linear dimensions of bodies, and compression is accompanied by their reduction. The value characterizing these processes is called body lengthening. Denote it by "x". The formula of elastic force is directly related to elongation. Each body undergoing deformation has its own geometric and physical parameters. The dependence of the elastic deformation resistance on the properties of the body and the material from which it is made is determined by the coefficient of elasticity, we call it stiffness (k).
The mathematical model of elastic interaction is described by Hooke's law.
The force arising from the deformation of the body is directed against the direction of displacement of individual parts of the body, is directly proportional to its elongation:
- F y = -kx (in vector notation).
The “-" sign indicates the opposite of the direction of deformation and force.
In scalar form, the negative sign is absent. The elastic force, the formula of which has the following form F y = kx, is used only for elastic deformations.
The interaction of the magnetic field with the current
The effect of a magnetic field on direct current is described by Ampere's law. In this case, the force with which a magnetic field acts on a conductor with a current placed in it is called the Ampere force.
The interaction of a magnetic field with a moving electric charge causes a force manifestation. The Ampere force, the formula of which is of the form F = IBlsinα, depends on the magnetic field induction (B), the length of the active part of the conductor (l), the current strength (I) in the conductor and the angle between the direction of current and magnetic induction.
Due to the latter dependence, it can be argued that the vector of the magnetic field can change when the conductor rotates or the current direction changes. The rule of the left hand allows you to set the direction of action. If the left hand is positioned so that the magnetic induction vector enters the palm of your hand, four fingers are directed by the current in the conductor, then the thumb bent 90 ° will show the direction of the magnetic field.
The application of this effect by mankind has been found, for example, in electric motors. The rotation of the rotor is caused by a magnetic field created by a powerful electromagnet. The force formula allows you to judge the possibility of changing engine power. With increasing current or field strength, the rotational moment increases, which leads to an increase in engine power.
Particle trajectories
The interaction of a magnetic field with a charge is widely used in mass spectrographs in the study of elementary particles.
The action of the field in this case causes the appearance of a force called the Lorentz force. When a charged particle moving at a certain speed enters a magnetic field , the Lorentz force, whose formula has the form F = vBqsinα, causes the particle to move around the circle.
In this mathematical model, v is the particle velocity modulus, whose electric charge is q, B is the magnetic induction of the field, and α is the angle between the directions of velocity and magnetic induction.
The particle moves in a circle (or in an arc of a circle), since the force and speed are directed at an angle of 90 ° to each other. Changing the direction of linear velocity causes the appearance of acceleration.
The rule of the left hand, discussed above, also holds true when studying the Lorentz force: if the left hand is positioned so that the magnetic induction vector enters the palm of the hand, four fingers extended in a line are directed along the speed of a positively charged particle, then bent 90 ° the thumb will show the direction of the force.
Plasma problems
The interaction of the magnetic field and matter is used in cyclotrons. The problems associated with laboratory studies of plasma do not allow it to be contained in closed vessels. Highly ionized gas can exist only at high temperatures. It is possible to hold the plasma in one place in space by means of magnetic fields, twisting the gas in the form of a ring. Controlled thermonuclear reactions can be studied by spinning a high-temperature plasma into a cord using magnetic fields.
An example of the action of a magnetic field in natural conditions on an ionized gas - Aurora. This magnificent spectacle is observed behind the Arctic Circle at an altitude of 100 km above the earth's surface. Mysterious colorful glow of gas could be explained only in the twentieth century. The magnetic field of the earth near the poles cannot prevent the penetration of the solar wind into the atmosphere. The most active radiation directed along the lines of magnetic induction causes ionization of the atmosphere.
The phenomena associated with the movement of charge
Historically, the main quantity characterizing the flow of current in a conductor is called the current strength. Interestingly, this concept has nothing to do with power in physics. The current strength, the formula of which includes a charge flowing per unit of time through the cross section of the conductor, has the form:
- I = q / t, where t is the charge flow time q.
In fact, current is the magnitude of the charge. The unit of its measurement is Ampere (A), in contrast to N.
Definition of work force
Forceful effect on the substance is accompanied by the completion of work. The work of force is a physical quantity numerically equal to the product of force and displacement under its action and the cosine of the angle between the directions of force and displacement.
The sought-after work of force, the formula of which has the form A = FScosα, includes the magnitude of the force.
The action of the body is accompanied by a change in body speed or deformation, which indicates simultaneous changes in energy. The work of force directly depends on the value.