In mechanics, why is it said that there is no difference between the size of objects?

In mechanics, there is a distinction between large and small objects. However, in order to simplify the problem in the mechanics problem, two mechanical models are set up (which are hypothetical), one is the mass point, and the other is the rigid body. Particle refers to having mass but no size, which is mostly used to describe the motion law of an object; A rigid body is one that does not change its shape under any external force, and is usually used to study the rotation of an object and the force on each part.

In middle school textbooks, because they are initially exposed to mechanical problems and mainly study the motion of objects, the objects in mechanics are regarded as particles without considering their shape and size, that is, there is no difference in size of objects as you say.

Because mechanics is the study of the force at a specific point, it is not directly related to the size of the object.

Because in mechanics, it is stipulated that an object with a certain mass can be regarded as a particle to be studied. Regardless of whether the object is large or small, in mechanics, it is concerned with the position of its center of gravity and its mass, and finally its center of gravity is used to represent the whole object, and the mass of the center of gravity is the mass of the whole object.

Because for some studies, the size of the object does not affect the study, so it is abstracted as a particle, i.e., a point with only mass and no size...

Mechanics stipulates that objects are treated as particles in force analysis.

Two iron balls hit the ground at the same time That's why!!

There should be a difference in quality.

Mechanics stipulates that objects are regarded as particles when analyzing forces, and if you don't understand the meaning of particles, you can read textbooks.

1. The pressure of the object on the table is equal to the support force of the table against the object (the force is mutual).

2. The object is at rest and the force is balanced, and the first number of space-time is only supported by the force and gravity, so the support force is equal to the gravitational force.

Combining the above two points, gravity equals the support force equals the pressure bucket head.

1.Regard the "remaining force with the resultant force of the mind" as "a force f1", and the original object is balanced at a high level, then it is known that the "force f1" and the "withdrawn force" are balanced forces, and after the "withdrawn force" is removed, the "one force f1" will not change, of course, it will continue to be equal to the withdrawn force, and the direction is opposite.

2.The net force is zero, which only means that acceleration cannot be generated, that is, the "effect of changing the state of motion of the object" is 0, but the effect of "changing the shape of the object" cannot be eliminated.

There are two effects of force, and when considering the effect of "changing the shape of an object", the object cannot be regarded as a particle, and "the net force is zero" does not make sense.

Question 1: Is it true that the greater the thrust, the greater the speed? Answer:

No. According to Newton's first law of motion: "If an object is not subject to force or the net force is zero, the object always remains at rest or moves in a uniform straight line." So, even if an object has velocity, it does not necessarily have a forceful effect.

Second question: "If it is pushed by a force of 20n in the horizontal plane,......."Answer: In the process of acceleration, there must be a force acting on it, for example, if you used to push it with a force of 10N, and keep the net force at zero, so that the object moves at a uniform speed, when you increase the force, from 10n to 20N, the object starts to accelerate by the force, and when you reach a force of 20N, it continues to move at a constant speed.

Question 3: "What is the difference between the left and right wiring of a switch or electrical appliance?" Answer:

There is no difference (under normal circumstances), because it depends on whether the left post goes into the live wire or the right post goes into the live wire. However, there are some special originals that are connected in the direction, or the switch plays some special role, which is another matter.

Choosing C requires the tensile force to give way to F, which should be solved with the lever equilibrium area, the fulcrum is E, and the equation can be listed as follows:

ql 2=2*7fl 8 where the total length is l

f=2n

As for the binding force required at E, as long as Brother Tannai balances the force, he can easily get 3N