Is dissipative force internal force

1. The work done by conservative internal force is the change of potential energy, only external force, conservative internal force and non conservative internal force
we have defined 0 potential energy as the earth's surface, and defined gravity as conservative force. Therefore, we have the conclusion that the work done by gravity can increase potential energy. (it implies that gravity is the internal force of the system).
first of all, we need to know what force the internal force belongs to, Because the internal force is proced when the objects contact each other (under a kind of environment), it can be explained by non relativistic Newtonian mechanics Relativity refers to the energy conversion of objects in different environments (coordinate systems), while Newtonian mechanics refers to the energy change of objects in one environment (coordinate system)< After that, we should know the principle of force:
I. force in the environment is the effect of an object on an object, and force cannot exist alone without the object. There may also be a force between two objects that are not in direct contact
force is the external cause of acceleration or deformation
Newton's second law of non relativistic mechanics can be written as: F = ma< 2. The action of force on the object has the action of external force on some scattered points or areas of some surfaces
in the interior of an object, there are reactions generated by external forces or internal binding forces e to the deformation of the object. These internal deformation constraints are generated in pairs, together they offset each other and do not affect the acceleration
it has the function of distributing force in the internal parts. These forces are generally proportional to the mass of each part. For example, the force proced by weight and the inertial force caused by acceleration are all forces distributed in the body, which are generally called physical force, or physical force for short< 3. The distinction of forces on an object:
1. If the external forces on the object converge, the resultant force must be equal to the physical strength and in the opposite direction
2. If the resultant force passes through the center of mass of the object, the resultant force must be equal to the total mass multiplied by the acceleration of the object. The size and the direction of the action line are the same as the original resultant force, except that the action line shifts to the position passing through the mass center of the object, causing the acceleration motion of the mass center of the object
3. The resultant force of these converging external forces does not pass through the center of mass of the object. The resultant force can be transformed into the sum of a force acting on the center of mass and a couple moment around the center of mass. The moment of couple is equal to the vertical distance from the resultant force multiplied by the center of mass to the original line of action of the resultant force, which causes the angular acceleration of the object to rotate around the center of mass
knowing these, we can know that the energy change of internal force in non relativistic Newtonian mechanics can also be explained by relativistic energy conversion
we know that:
conservative force is the force that does work related to the path, also known as dissipative force, which is opposite to conservative force. For example, when friction does work, it will generate heat when it goes through each journey. When it returns from point a to point B, the work is not zero. When gravity returns from point a to point B, the work is zero. In this case, friction is non conservative force, and gravity is conservative force
then the non conservative internal forces can be distinguished by energy
there are many of these forces, which can be found by subtracting the released energy from the energy used in mechanical work A lot, I can't finish, only define.)

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3.

Difference between internal force and stress:

1. Internal force: internal force refers to the force that causes internal interaction of components under the action of external force. Internal force is closely related to the strength, stiffness and stability of components, so it is very important to study the internal force of components

Stress: when an object is deformed e to external factors (stress, humidity, temperature field change, etc.), the internal force of the interaction between various parts of the object is generated to resist the effect of the external factors, and the object is tried to recover from the position after deformation to the position before deformation

The internal force is the interaction between the parts of the same body. Stress is a vector, the component along the normal direction of the cross section is called normal stress, the component along the tangential direction is called shear stress, and the stress of a point in the body in all possible directions is called the stress state of the point

When the internal force and stress appear at the same time, the internal force is generally used to represent the combined effect of the force on the member section, such as bending moment, shear force, axial force, etc., while the stress represents the force on the unit area of the member section, such as normal stress and shear stress

4. Internal force and external force depend on the system you study. The force that interacts in the system is internal force, otherwise it is external force

conservative force and non conservative force depend on whether the work is related to the path
dissipative force can't satisfy the conservation of mechanical energy. Dissipative force must belong to non conservative force. Common non conservative forces are dissipative force, but not all of them are.

5. This problem depends on how the system is determined. For example, two objects are connected by a rope and move at variable speed.
if you only look at a or B, then the force of the rope is an external force. If AB is regarded as a system, then the force of the rope is an internal force
the integral method and the partial method are to analyze the whole system first, to avoid the influence of complex internal forces, to calculate the acceleration and so on, and then analyze the single object separately to get the results
my answer is... Internal force is the interaction force inside the system. Without a clear system, it can not be divided into internal force and external force.

6. No one says that internal force does not do work, but that internal non dissipative force does work, which will not increase the overall mechanical energy. But you have to consider the movement of the indivial in the whole, and naturally you have to consider all the forces that the indivial receives

while the work done by the dissipative force will lead to the transformation of the whole mechanical energy into internal energy and chemical energy, resulting in the rection of mechanical energy (kinetic energy plus potential energy)

and it should be noted that no matter dissipative or conservative internal forces, internal forces appear in pairs, because momentum is the accumulation of force on time, and two internal forces with the same size and opposite direction will not change the momentum of the system. If the overall momentum is zero at the beginning and there is no external force to do work on the system, the momentum of the system is always conserved and the position of the center of mass is conserved. It is convenient for us to study some cases
for example, if an explosion occurs inside a stone in the universe and it splits into two pieces, as long as you know the velocity and position of one piece, you can infer the position and velocity of the other stone according to the conservation of momentum and the conservation of center of mass, regardless of the specific details of the force between them. It is not necessary to calculate how it accelerates and decelerates in the process according to the equation of motion. This is a very convenient way.

7. One is the macro concept, and the other is the micro concept, which I think cannot be confused. The internal force should be the comprehensive macroscopic expression of various forces between molecules or even atoms. Including van der Waals force, hydrogen bond, etc. For polymer, the rotation of chemical bond also determines the mechanical properties of materials to a certain extent; For metal materials, in chemistry, it is generally considered that metal bond is a kind of chemical bond. In material mechanics, it doesn't matter. It is said that intermolecular force is calculated. Therefore, strictly speaking, chemical bond is also related to internal force of materials
or from another angle, you said that there would be no internal force without external force, but the intermolecular force exists all the time, which means that they are definitely different
the meaning of "internal force is related to intermolecular force" is actually very simple. When there is an external force, the material will proce the corresponding internal force, but how can a material proce the force itself? Who is the object of force? The answer is the molecules there, the interactions between the molecules. What is the form of their role? The intermolecular force, of course.

8. The first problem is that the internal force of the rod can only be calculated along the direction of the rod, the three forces are balanced, and there are angles, so it's easy to calculate it.
the second problem is to take the whole as the research object, take the moment of point a, calculate the vertical force of point B, the vertical force of point a is zero, calculate the vertical force of point a, and then take the moment of point C, because point C is hinged, the resultant moment is zero, plus the horizontal resultant force is f, Two equations, two unknowns come out. Pay attention to the direction

9. The common conservative forces are gravity, spring elastic force, electrostatic field force and universal gravitation; Non conservative force: sliding friction.

10.

Internal force is the interaction force within the system

example 1: if the earth and the object form a system, the gravity on the object is the internal force

example 2: when two objects collide, the two objects are a system, and the forces that collide with each other are internal forces

the external force is the force outside the system. For example, in example 2, a force F causes one of the objects to collide with another when accelerating, and this force F is the external force

extended data:

the internal force is the interaction force in the system. For example, a compression spring is placed between two objects on a smooth horizontal plane, and the force of the spring on the two objects after release is the internal force of the system composed of the two objects. The interaction force between the stars in the solar system is the internal force in the solar system

the internal force is that the initial state of each part or particle inside the object changes under the action of external factors, such as external force and temperature change, and the adjacent parts or particles inside the object proce interaction force, which is the internal force