Calculation quality

1.

1. Gravity g = mg

(vertically downward, g = 9.8m/s2 ≈ 10m / S2, the action point is at the center of gravity, applicable to the earth surface)

2. Hooke's law f = KX

{along the recovery deformation direction, K: stiffness coefficient (n / M), X: deformation variable (m)}

3. Sliding friction force F = μ FN

{opposite to the relative motion direction of the object, μ： Friction coefficient, FN: positive pressure (n)}

{rrrrrrr}

extended data:

different classification of force

1. According to the nature of force, it can be divided into gravity, universal gravitation, elastic force, friction force, molecular force, electromagnetic force, nuclear force, etc Note that gravity is not equal to gravity under all conditions Gravity does not point to the center of the earth under all conditions. Gravity is a component of the earth's gravitational force on an object, and the other component is a centripetal force. Only on the equator does gravity point to the center of the earth.)

According to the effect of force, it can be divided into tension, tension, pressure, supporting force, power, resistance, centripetal force, restoring force, etc

According to the research object, it can be divided into external force and internal force

According to the action mode of force, it can be divided into non-contact force (such as gravitation, electromagnetic force, etc.) and contact force (such as elastic force, friction force, etc.)

There are four basic interactions (forces): gravitational interaction, electromagnetic interaction, strong interaction and weak interaction

nature of force:

materiality: force is the effect of an object (matter, mass) on an object (matter, mass). When an object is subjected to a force, another object must exert this effect on it. Force cannot exist independently without an object

interactivity (interaction): the interaction between any two objects is always mutual, and the object exerting the force must also be the object under the force. As long as one body exerts a force on another, the stressed body in turn will surely add a force to the exerted body Generating conditions: the force is equal in size (the resultant force is zero, in a state of non directional static motion) or not equal, in the opposite direction, acting on two different objects, and acting on the same straight line. It can be summarized as: foreign body, equivalent, reverse, collinear. A pair of interaction forces must proce and disappear at the same time.)

Vectoriality: force is a vector, which has both magnitude and direction

simultaneity: the force proced and disappeared at the same time

independence: the effect of one force does not affect the effect of another

includes three elements: the size, direction and action point of the force. The accurate expression of the three elements of force by a directed line segment is called the diagram of force. The size is represented by the length of a scaled line segment, the direction is represented by an arrow, the point of action is represented by an arrow or the tail of an arrow, and the straight line along which the direction of a force follows is called the line of action of a force. The diagram of the force is used for the calculation of the force. When the judgment power is large, we must pay attention to the scale of the line segment, because even if one line segment is longer than another line segment, but the scale of the long line segment is also longer, the force represented by the short line segment is not necessarily smaller than that represented by the long line segment

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3. Mass force is the force of a force field acting on all fluid particles, and its size is directly proportional to the mass or volume of the fluid, so it is called mass force or volume force. In life, our common mass force is gravity, linear motion inertia force, centrifugal inertia force
1. Gravity formula,
G = mg
g-gravity
n
m-mass
kg
G-acceleration of gravity
, constant 9.8m/s2
2. Inertial force formula of linear motion,
F = ma
m --- mass
kg
A --- acceleration M / S2
f --- inertial force
n
3. Centrifugal inertial force formula of rotating object,
F = Mr [(2 * 3.14 * n) / 60] * [(2 * 3.14 * n) / 60]
f-centrifugal force
n
m-unbalance mass
kg
r-Radial distance between unbalance quantity and rotation center
m
n-rotation speed
R / min

4. Gravity, inertial force of linear motion and centrifugal inertial force all belong to mass force. Mass force is the force of a force field acting on all fluid particles, and its size is directly proportional to the mass or volume of the fluid, so it is called mass force or volume force.

5.

Force (f) = mass (m) × Acceleration (a), Newton's second law of motion

The common expression of Newton's second law of motion: the acceleration of an object is directly proportional to the force, inversely proportional to the mass of the object, and directly proportional to the reciprocal of the mass of the object; The direction of acceleration is the same as that of the force

This law was put forward by Isaac Newton in 1687 in the Book Mathematical Principles of natural philosophy. Newton's second law of motion and the first and third laws together constitute Newton's law of motion, which expounds the basic law of motion in classical mechanics

Some dynamic problems can be solved by applying Newton's second law of motion. There are two main types of problems:

1. In the first type, the mass and motion state of the particle are known, and the position of the particle at any time is known, that is, the equation of motion or the expression of velocity or acceleration. Generally, the second derivative of the known equation of motion over time or the first derivative of the velocity equation over time is used to calculate the acceleration, Then the unknown force is calculated according to Newton's second theorem

In the second kind of problems, the mass of the particle and the force acting on the particle are known, and the motion state of the particle is calculated, that is, the motion equation, the velocity expression or the acceleration expression. Generally, the equation is listed by Newton's second law of motion, and the acceleration expression of the object is obtained, The equation of motion is obtained by definite integral

6. F = ma, which only means that the force can not change the mass, can only change the acceleration, the mass is the object itself, has nothing to do with the force

7. Newton's second law: F = ma

8. In fact, the most accurate way to measure mass is to multiply volume by density, M = VQ, which you should know clearly
but no one in our life calculates it in this way, which is too inconvenient
as for how Newton's second law comes from, I guess you are confused at present, and I don't have a deep research in this aspect
but it's easy to understand through life practice, just like an object has been stressed, Its speed will be faster and faster, with acceleration. Acceleration is generated by force, and it is consistent with the direction of force. At the same time, you will also find that the same force acts on objects with different masses, and the acceleration of objects is different. Which one is faster to push a small wooden box or a large wooden box
since Niu Er is known as the law, he doesn't ask you to reason in high school, you just accept it.
if you are interested, you can push it again when you have a wide range of knowledge, and it's good to question the authority. But for high school physics learning, if you are at the top of the bull's horn and tangle about whether a law is correct, you will go into a misunderstanding, In this way, physics is basically destroyed, and all doubts are based on understanding, that is, you have to learn how to use it first, and find out their irrationality in the process. Only in this way can doubts be justified

in fact... I'm the wine sword Xiaoyao upstairs.... I don't know why I can't change the answer... So I changed the number

9.

M (mass) = P (density) V (volume)

m (mass) = g (gravity) / g (9.8N / kg)

for example, the length of a rectangular lead block Α wide Β high Ρ， Look up the table to get the density ρ， Then the mass m= Α×Β×Ρ×ρ

m refers to mass in gram (g); P is the density in gram per cubic meter (g / cm & # 179;); V is the volume in cubic meters (CM & # 179;)

The mass of a substance with

unit mass is called molar mass, which is indicated by the symbol M. When the mass of a substance is in mol, the unit of molar mass is g / mol, which is equal to the atomic or molecular mass of the substance in number

for a certain compound, its molar mass is fixed. The quality of matter changes with the amount of matter

The mass of a substance with

unit mass is called molar mass, which is represented by the symbol M When the mass of a substance is expressed in grams, it is numerically equal to the relative atomic or molecular mass of the substance

< H2 > extended data

source

the quantity of a substance is a physical quantity, which means the aggregate containing a certain number of particles, and the symbol is n. The unit of quantity of a substance is mole. In science, the Avogadro constant (about 6.02 0 × 10²&# 179; The collective of particles as a unit is called mole. The number of particles in 1 mol of different substances is the same, but e to the different mass of different particles, the mass of different substances in 1 mol is also different

In 1971, the Fourteenth International Conference on Metrology defined mole in the following two paragraphs: "mole is the amount of matter in a system, and the number of basic units in the system is equal to the number of atoms of 0.012kg carbon-12."

"when using mole, the basic unit should be specified, which can be atoms, molecules, ions, electrons and other particles, or a specific combination of these particles." The last two paragraphs should be regarded as a whole. The number of carbon atoms contained in 0.012kg carbon 12 is the Avogadro constant (NA), and the approximate value measured in the experiment is Na = 6.021687126645 × 10²&# 179; Different from ordinary units, mole has one characteristic:

it measures microscopic basic units, such as ions, but cannot be used to measure substances

When

1mol, it takes Avogadro number as the unit of measurement, which is a batch, not the number of molecules, atoms and other particles. It can also be used to measure specific combinations of micro particles,

for example, the amount of sulfuric acid in mole, i.e. 1 mol of sulfuric acid contains 6.02% × 10²&# 179; It's a molecule of sulfuric acid. Mole is the most widely used unit of measurement in chemistry, such as calculation of chemical reaction equation, calculation in solution, preparation and dilution of solution, calculation of chemical equilibrium, molar volume of gas and thermochemistry

molar mass is the mass of a substance divided by the amount of a substance, in grams per mole, and molar volume is the volume of a substance divided by the amount of a substance, in cubic meters per mole. The commonly used molar atomic weight, molar weight and molar volume should be abolished

the molar mass and molar volume are the derived quantities of the quantity of a substance, and the basic unit must be specified in the application. For the same substance, if the basic unit is different, the molar mass and molar volume will be different

although Avogadro constant is a large value, it is very convenient to use mole as the unit of mass, which is like a bridge linking microscopic particles with macroscopic matter

10. N depends, M = PV