The word "power" is so all-encompassing that to give it a clear concept is an almost impossible task. The variety from muscle strength to the strength of the mind does not cover the full range of concepts invested in it. Force, considered as a physical quantity, has a well-defined meaning and definition. The force formula defines a mathematical model: the dependence of force on the main parameters.
The history of force research includes the definition of dependence on parameters and experimental proof of dependence.
Power 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 the speed or deformation of bodies.
As a physical quantity, force has a unit of measurement (in the SI system - Newton) and a device for measuring it - a dynamometer. The principle of operation of the force meter is based on comparing the force acting on the body with the force of the spring force of the dynamometer.
A force of 1 newton is taken as a force under which a body of mass 1 kg changes its speed by 1 m in 1 second.
Force as a vector quantity is defined:
- direction of action;
- application point;
- module, absolutesize.
Describing the interaction, be sure to indicate these parameters.
Types of natural interactions: gravitational, electromagnetic, strong, weak. Gravitational forces (the force of universal gravitation with its variety - the force of gravity) exist due to the influence of gravitational fields surrounding any body that has 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 larger range of forces arises from the electromagnetic interaction of the atoms that make up matter.
Pressure force
When a body interacts with the Earth, it exerts pressure on the surface. The pressure force, the formula of which is: P=mg, is determined by the body mass (m). Gravitational acceleration (g) has different values at different latitudes of the Earth.
The force of vertical pressure is equal in absolute value and opposite in direction to the force of elasticity arising in the support. The force formula changes depending on the movement of the body.
Change in body weight
The action of a body on a support due to interaction with the Earth is often referred to as the weight of the body. Interestingly, the amount 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 free fall, an increase in weight is observed. If the acceleration of the body coincides with the direction of free fall, then the weight of the body decreases. For example, while in an ascending elevator, at the beginning of the ascent, a person feels an increase in weight for a while. Assert that its masschanges, it doesn't. At the same time, we separate the concepts of "body weight" and its "mass".
Elastic force
When changing the shape of a body (its deformation), a force appears that tends 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.
Let's consider the simplest deformation: tension and compression. Tension is accompanied by an increase in the linear dimensions of the bodies, while compression is accompanied by their decrease. The value characterizing these processes is called body elongation. Let's denote it by "x". The elastic force formula is directly related to elongation. Each body subjected to deformation has its own geometric and physical parameters. The dependence of the elastic resistance to deformation on the properties of the body and the material from which it is made is determined by the coefficient of elasticity, let's 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:
- Fy=-kx (vector notation).
The "-" sign indicates the opposite direction of deformation and force.
There is no negative sign in scalar form. The elastic force, the formula of which has the following form Fy=kx, is used only for elastic deformations.
Interaction of magnetic field with current
Influencemagnetic field to direct current is described by Ampère's law. In this case, the force with which the magnetic field acts on a current-carrying conductor 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 F=IBlsinα, depends on the magnetic induction of the field (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 the current and the magnetic induction.
Due to the last dependence, it can be argued that the vector of the magnetic field can change when the conductor is rotated or the direction of the current changes. The left hand rule allows you to set the direction of action. If the left hand is positioned so that the magnetic induction vector enters the palm, four fingers are directed along the current in the conductor, then the thumb bent by 90° will show the direction of the magnetic field.
The use 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 the engine power. With an increase in current or field strength, the torque increases, resulting in an increase in motor 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 calledLorentz force. When a charged particle moving at a certain speed enters a magnetic field, the Lorentz force, the formula of which has the form F=vBqsinα, causes the particle to move in a circle.
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, α is the angle between the directions of velocity and magnetic induction.
The particle moves in a circle (or an arc of a circle), since force and speed are directed at an angle of 90° to each other. Changing the direction of the linear velocity causes the appearance of acceleration.
The rule of the left hand, discussed above, also takes place when studying the Lorentz force: if the left hand is positioned so that the magnetic induction vector enters the palm, four fingers extended in a line are directed along the speed of a positively charged particle, then the thumb bent 90° shows the direction of the force.
Plasma issues
Interaction of magnetic field and matter is used in cyclotrons. The problems associated with the laboratory study of plasma do not allow it to be kept in closed vessels. A highly ionized gas can only exist at high temperatures. Plasma can be kept in one place in space by means of magnetic fields, twisting the gas in the form of a ring. Controlled thermonuclear reactions can also be studied by spinning high-temperature plasma into a filament using magnetic fields.
An example of the action of a magnetic fieldin natural conditions on ionized gas - Aurora Borealis. This majestic spectacle is observed beyond the Arctic Circle at an altitude of 100 km above the earth's surface. The mysterious colorful glow of gas could only be explained in the 20th century. The earth's magnetic field near the poles cannot prevent the solar wind from penetrating the atmosphere. The most active radiation directed along the lines of magnetic induction causes ionization of the atmosphere.
Phenomena associated with charge movement
Historically, the main quantity that characterizes the flow of current in a conductor is called the current strength. Interestingly, 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, is:
I=q/t, where t is the charge flow time q
In fact, the current strength is the amount of charge. Its unit of measurement is Ampere (A), unlike N.
Determining the work of a force
Force action on a substance is accompanied by the performance of work. The work of a force is a physical quantity numerically equal to the product of the force and the displacement passed under its action, and the cosine of the angle between the directions of the force and displacement.
The desired work of the force, the formula of which is A=FScosα, includes the magnitude of the force.
The action of the body is accompanied by a change in the speed of the body or deformation, which indicates simultaneous changes in energy. The work done by a force depends onvalues.
