Unclear understanding of the causes of frictional heat generation

When applying the law of conservation of energy to the entire process, the changes in various energies of the system are incompletely analyzed, and the possible loss of mechanical energy at certain moments is ignored.

Confusing the law of conservation of energy (energy on both sides of the equation) with the functional relationship (work on one side of the equation and energy on the other side)

The difference between the law of conservation of mechanical energy and the kinetic energy theorem

The relationship between work and energy conversion

The conservation condition is never that the work done by the combined external force is equal to 0, nor that the work done by the combined external force is 0.

The work done by gravity or elastic force cannot cause the conversion of mechanical energy and other forms of energy. It can only convert the kinetic energy and potential energy in the system into each other. The work done by other forces except gravity and elastic force can cause the conversion of mechanical energy and other forms of energy.

For an object, if only gravity does work and other forces do no work, then the mechanical energy of the object is conserved.

From the perspective of energy conversion, only kinetic energy and thermal energy within the system are converted into each other. There is no transfer of mechanical energy between the system and the outside world, nor is it converted into other forms of energy (such as internal energy). Then the mechanical energy of the system is conserved. Is energy conserved?

From the perspective of work, an object system includes internal and external forces. Only gravity or elastic force does work, other forces do no work or the sum of the work done is 0

Some ropes are suddenly tightened and objects collide. Except for gravity or elastic force, other forces do no work or the sum of the work is 0.

Select the research object (object or system) according to the meaning of the question

Clearly study the movement process of the object, analyze the force received by the object during the process, clarify the work done by each force, and determine whether mechanical energy is conserved.

Appropriately select the zero potential energy surface to determine the mechanical energy of the research object's initial and final states during the research process.

Solving the equations based on the expression of the law of conservation of mechanical energy

When the energy of an object decreases, there must be an increase in the energy of other objects, and the amount of decrease must be equal to the amount of increase.

When some form of energy decreases, there must be other forms of energy increase, and the amount of decrease must be equal to the amount of increase.