All the formulas of physics about force, what are the formulas of physical mechanics

3. Force (common force, force synthesis and decomposition).

1) Common forces.

1.Gravitational force g mg (direction straight down, g, the point of action is at the center of gravity, applicable near the earth's surface).

2.Hooke's law f kx {direction along the direction of recovery deformation, k: stiffness coefficient (n m), x: deformation variable (m)}

3.The sliding friction force f fn {opposite to the relative direction of motion of the object, : friction factor, fn: positive pressure (n)}

4.Static friction 0 f static fm (opposite to the direction of the relative movement trend of the object, fm is the maximum static friction).

5.Gravitational force f gm1m2 r2 (g ?m2 kg2, the direction is on their line)

6.Electrostatic force f kq1q2 r2 (k ?m2 c2, the direction is on their line).

7.The electric field force f eq (e: field strength n c, q: electric charge c, the electric field force of the positive charge is in the same direction as the field strength).

8.Ampere force f bilsin (is the angle between b and l, when l b: f bil, b l: f 0).

9.Lorentz force f qvbsin (is the angle between b and v, when v b: f qvb, v b: f 0).

Note: 1) The stiffness coefficient k is determined by the spring itself;

2) The friction factor is not related to the pressure and the size of the contact area, but is determined by the material characteristics and surface condition of the contact surface.

3) Fm is slightly greater than Fn, which is generally regarded as FM Fn;

5) Physical quantity symbol and unit B: magnetic inductance intensity (t), L: effective length (m), I: current intensity (a), v: charged particle velocity (m s), q: charged particle (charged body) charge (c);

6) Both the ampere force and Lorentz force direction are determined by the left-handed rule.

2) Synthesis and decomposition of forces.

1.The resultant force on the same straight line is in the same direction: f f1+f2, and the reverse is f f1-f2 (f1>f2).

2.Synthesis of mutually angular forces:

f(f12+f22+2f1f2cos)1 2 (cosine theorem) f1 f2: f(f12+f22)1 2

3.Net force magnitude range: |f1-f2|≤f≤|f1+f2|

4.Orthogonal decomposition of forces: fx fcos, fy fsin ( is the angle between the resultant force and the x-axis tg fy fx).

Note: 1) The synthesis and decomposition of force (vector) follow the parallelogram rule;

2) The relationship between the resultant force and the component force is an equivalent substitution relationship, and the joint action of the component force can be replaced by the resultant force, and vice versa;

3) In addition to the formula method, it can also be used as a graph method to solve, at this time, the scale should be selected and the graph should be strictly made;

4) When the value of F1 and F2 is constant, the larger the angle (angle) between F1 and F2, the smaller the resultant force;

5) The synthesis of the force on the same straight line can be taken in the positive direction along the straight line, and the direction of the force can be expressed by plus and minus signs, which can be simplified into algebraic operations.

The physical mechanics formula is:

1. Momentum moment theorem: f=ma (the combined external force provides the acceleration of the object.

2. Kinetic energy theorem.

w = 1 2mv 2-1 2mv 2 (the work done by the combined external force is equal to the amount of change in the kinetic energy of the object);

3. Momentum theorem.

ft = mv-mv (the impulse of the resultant external force is equal to the change in the momentum of the object).

The theorems with obvious physical significance derived from Newton's differential equations of motion include the momentum theorem, the momentum moment theorem, the kinetic energy theorem, and the centroid wheel base shouting theorem.

The basics of kinetics

Particle dynamics, particle system dynamics, rigid body dynamics, D'Alembert's principle.

Wait. Applied disciplines developed on the basis of dynamics include celestial mechanics, vibration theory, motion stability theory, gyro-wax mechanics, external ballistics, variable mass mechanics, and the dynamics of multi-rigid body systems in development (see Vibration, Fengkai Motion Stability, Variable Body Motion, and Multi-rigid Body Systems).

There are two basic types of problems in particle dynamics: one is to find the force acting on the particle with the known motion of the particle, and the other is to find the motion of the particle with the known force acting on the particle, and only the second derivative of the equation of motion of the particle is required to solve the first type of problem.

The acceleration of the particle is obtained, and Newton's second law is substituted.

You can find power.

The mechanics formula isHooke's LawHooke's law, f=kx, x is the elongation or compression, and k is the stubbornness coefficient.

It is only related to the original length, thickness and material of the spring, gravity, g = mg, g varies with height and latitude, the formula of friction, sliding friction f = n, static friction, the equilibrium condition told by the object sock or Newton's second law.

solve, independent of positive pressure.

Magnitude range, o f static fm, fm is the maximum static friction, related to positive pressure, buoyancy, f = vg, unit of attention, gravitational force.

f=g。<>

Introduction to physics

Physics is a fundamental science.

It is a discipline that studies the most general laws of the motion of matter and the basic structure of matter. Physics is a regular summary of people's knowledge of the transformation of matter in inanimate nature. There should be two kinds of such movements and transformations.

The first is the extension of people's sensory vision, and the second is the invention and creation of scientific instruments for observation and measurement in modern times.

The results of the experiment are based on the indirect understanding of the internal composition of matter. As a leading discipline in the natural sciences, physics studies everything from the universe to elementary particles.

and the most basic forms and laws of motion of all matter, so they have become the basis for the study of other natural science disciplines.

The physical mechanics formula is:

1. Momentum moment theorem: f=ma (the combined external force provides the acceleration of the object.

2. Kinetic energy theorem: w=1 2mv 2-1 2mv 2 (the work done by the combined external force is equal to the change in the kinetic energy of the object);

3. Momentum theorem: ft=mv-mv (the impulse of the combined external force is equal to the change in the momentum of the object).

Theorems with obvious physical significance derived from Newton's differential equations of motion include the momentum theorem, the momentum moment theorem, the kinetic energy theorem, and the centroid motion theorem.

The basics of kinetics

Particle dynamics, particle system dynamics, rigid body dynamics, D'Alembert's principle, etc. Applied disciplines based on dynamics include celestial mechanics, vibration theory, motion stability theory, gyromechanics, external ballistics, variable mass mechanics, and the dynamics of multi-rigid body systems under development (see Vibration, Motion Stability, Variable Body Motion, and Multi-Rigid Body Systems).

There are two basic problems in particle dynamics: one is to find the force acting on the particle after knowing the motion of the point, and the other is to find the force acting on the particle point, and the other is to find the motion of the particle point, and when solving the first type of problem, you only need to take the second derivative of the equation of motion of the particle point to obtain the acceleration of the particle point, and substitute Newton's second law to obtain the force.

The mechanical formulas are:

Hooke's law: f = kx (x is the amount of elongation or compression, k is the coefficient of stubbornness, and is only related to the original length, thickness and material of the spring).

Gravity: g = mg (g varies with altitude, latitude).

Formula for friction:

1) Sliding friction: f= kn.

2) Static frictional bibliotic force: Solved by the equilibrium condition of the object or Newton's second law, independent of the positive pressure.

Mechanics skills: 1. It is said that the learning of physics is interconnected, and the learning of physical mechanics also plays a very important role in the learning of later knowledge, which is not only the use of a theorem formula to enter the Ming scattered line assessment.

2. Rather, it is to master the relevant knowledge by synthesizing various theorems, so it is necessary to effectively transform the relevant knowledge points in the learning of mechanics-related knowledge, and establish a learning network in itself.