Force formula. Strength - the formula (physics)

The word "power" is so comprehensive that giving it a clear concept is a practically impossible task. Variety from the strength of the muscles to the power of the mind does not cover the whole range 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 the force on the basic parameters.

The history of force research includes the definition of dependence on parameters and the experimental proof of the dependence.

Strength in physics

Strength is a measure of the interaction of bodies. The mutual action of bodies on each other completely describes the processes associated with the change in velocity or deformation of bodies.

As a physical quantity, the force has a unit of measurement (in the SI system - Newton) and the device for its measurement is a dynamometer. The principle of the silometer is based on the comparison of the force acting on the body, with the spring force of the dynamometer.

For force in 1 newton a force is adopted, under the action of which a body with a mass of 1 kg changes its velocity by 1 m in 1 second.

Force as a vector quantity is determined by:

• Direction of action;
• The point of application;
• Module, absolute value.

Describing the interaction, you must specify these parameters.

Types of natural interactions: gravitational, electromagnetic, strong, weak. Gravitational forces (the force of universal gravitation with its variety - gravity force) exist due to the influence of the gravitational fields surrounding any body having mass. The investigation of gravity fields has not been completed so far. It is not yet possible to find the source of the field.

A greater number of forces arise due to the electromagnetic interaction of atoms, of which the substance consists.

Force of pressure

When the body interacts with the Earth, it exerts pressure on the surface. The force of pressure, the formula of which has the form: P = mg, is determined by the mass of the body (m). The acceleration of free fall (g) has different values at different latitudes of the Earth.

The vertical pressure force is equal in modulus and opposite in direction to the elastic force arising in the support. The force formula in this case varies depending on the movement of the body.

Change in body weight

The action of the body on the support due to interaction with the Earth is often referred to as body weight. Interestingly, the amount of body weight depends on the acceleration of motion in the vertical direction. In the case when the acceleration direction is opposite to the acceleration of free fall, an increase in weight is observed. If the acceleration of the body coincides with the direction of free fall, then the body weight decreases. For example, while in a climbing elevator, at the beginning of the climb a person feels a weight gain for a while. It is not necessary to say that his mass is changing. At the same time we share the concepts of "body weight" and its "mass".

Strength of elasticity

When the shape of the body (its deformation) changes, a force appears, which tends to return the body to its original form. This force was given the name "strength of elasticity". It arises because of the electrical interaction of particles, of which the body consists.

Consider the simplest deformation: stretching and contraction. Stretching is accompanied by an increase in the linear dimensions of the bodies, and compression is accompanied by a decrease. The magnitude characterizing these processes is called the elongation of the body. Denote it by "x". The elastic force formula is directly related to the elongation. Every body that undergoes 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 elasticity coefficient, let's call it the rigidity (k).

The mathematical model of elastic interaction is described by Hooke's law.

The force arising from deformation of the body is directed against the direction of displacement of individual parts of the body, directly proportional to its elongation:

• F _y = -kx (in the vector notation).

The "-" sign indicates the opposite of the direction of deformation and force.

In the scalar form, there is no negative sign. The elastic force, the formula of which has the following form F _y = kx, is used only for elastic deformations.

Interaction of a magnetic field with a current

The influence of the magnetic field on the direct current is described by the Ampere law. In this case, the force with which the 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 Ampère force, whose formula has the form F = IBlsinα, depends on the magnetic induction of the field (B), the length of the active part of the conductor (l), the current (I) in the conductor and the angle between the direction of the current and the magnetic induction.

Due to the latter dependence, it can be asserted that the action vector of the magnetic field can change when the conductor is rotated or the direction of the current is changed. The left hand rule allows you to set the direction of the action. If the left hand is placed in such a way that the vector of magnetic induction enters the palm, the four fingers are directed along the current in the conductor, then the thumb twisted by 90 ^° will show the direction of the action of the magnetic field.

The use of this influence by mankind is found, for example, in electric motors. 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 the engine power. With increasing current strength or field size, the torque increases, which leads to an increase in the 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 Lorentz force, moving with a certain velocity of a charged particle, hits the magnetic field , the formula of which has the form F = vBqsinα, causes the particle to move along the circumference.

In this mathematical model, v is the velocity modulus of a particle 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 along a circle (or an arc of a circle), since the force and speed are directed at an angle of 90 ^{° to} each other. The change in the direction of the linear velocity causes the appearance of acceleration.

The rule of the left hand, considered above, takes place also in the study of the Lorentz force: if the left hand is positioned in such a way that the vector of magnetic induction enters the palm, four fingers stretched in a line were directed along the velocity of the positively charged particle, then bent by 90 ^° The thumb will show the direction of the action of the force.

Problems of plasma

The interaction of the magnetic field and matter is used in cyclotrons. Problems associated with laboratory studies of plasma, do not allow to contain it in closed vessels. Highly ionized gas can exist only at high temperatures. To keep the plasma in one place of space it is possible by means of magnetic fields, twisting the gas in the form of a ring. Controllable thermonuclear reactions can be studied, also by twisting high-temperature plasma into a cord by means of magnetic fields.

An example of the action of a magnetic field in natural conditions on an ionized gas is Polar Lights. This majestic spectacle is observed beyond the Arctic Circle at an altitude of 100 km above the earth's surface. Mysterious colorful glow of gas could only be explained in the twentieth century. The magnetic field of the earth near the poles can not 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 motion of a charge

Historically, the main value characterizing the current flow in a conductor is called the current strength. It is interesting that this concept has nothing to do with force in physics. The current strength, the formula of which includes the charge flowing per unit time through the cross section of the conductor, looks like:

• I = q / t, where t is the time of the charge q.

In fact, the current strength is the magnitude of the charge. The unit of its measurement is Ampere (A), in contrast to N.

Determining the work of force

Force action on the substance is accompanied by the performance of work. The work of force is a physical quantity that is numerically equal to the product of the force for the movement traversed by its action, and the cosine of the angle between the directions of force and displacement.

The required 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 magnitude.