In physics, there is such a thing as "power." It is simple, but quite capacious. In the physics course in the school curriculum, conservative and dissipative forces are distinguished. Or potential and non-potential. In order to navigate these concepts, to know their differences, examples, to answer the question: "Dissipative forces - what is this?" - it is necessary to study this topic in more detail.
What it is?
From the point of view of physics as a science of matter and the general laws of nature, force is one of the physical quantities, it characterizes the effect on the body under study by other bodies. There are many different kinds of forces. Electromagnetic, gravitational, centrifugal, intermolecular, etc. However, there is a classification of forces, which takes into account the work function as a characteristic for separation.
Dissipative forces are a variety of forces in which the work is dependent on the movement of the body, more precisely on the trajectory of this movement. In this case, the mechanical energy of this body goes into non-mechanical. The work of conservative forces does not depend on the trajectory of the body, it is zero. Dissipative forces are non-potential forces, and conservative ones are potential ones.
What are non-mechanical and mechanical forms of energy? How do they differ from each other?
Forms of energy
Energy in physics is called the quantity characterizing the forms of motion and interaction of matter, which is also a characteristic of the transition of matter from one form to another. There are such concepts as potential (rest energy, i.e., energy possessed by a body in a state of rest) and kinetic energy (energy of motion, i.e., energy of a body in motion), which in total form the total mechanical energy . What are non-mechanical forms? Such energy, which does not depend on the movement and position of the body under study. The most famous example of non-mechanical energy is thermal energy, which is characterized by heating / cooling of bodies.
Sliding friction
Examples of dissipative forces can be various forces, as a result of which the energy of the body passes from mechanical into non-mechanical forms of energy. The most capacious example of dissipative forces is that which arises between bodies that interact with each other, provided they move relative to each other. That is, the sliding friction force, as a result of which the bodies between which the interaction is studied, are heated, that is, mechanical energy goes into heat. There are several types of sliding friction:
- Dry - there is no lubricating layer between the surfaces of interacting bodies (liquid, gaseous, solid).
- Dry with dry lubricant - graphite powder is present as a solid lubricant between interacting bodies.
- Liquid - between the interacting bodies as a lubricant there is a layer of liquid or gas of various thicknesses.
- Mixed - between the interacting bodies, as a lubricant, there is a layer containing both dry and liquid lubricants.
- Boundary - between the interacting bodies there is a layer of various nature (for example, oxide films).
There is also a division into the internal (interacting layers of one body) and external (interaction between different bodies) friction forces.
Windage
A special case of friction forces is the force of aerodynamic drag of the air. This force is directly dependent on the speed of the body. More precisely, its square relative to air. In addition to being proportional to the square of the speed, the strength of air resistance depends on the surface area of the body, the density of the air itself, and also on the aerodynamic drag coefficient. Aerodynamic drag is independent of body weight.
In other words, the aerodynamic resistance of air is a kind of friction force between air and a body moving in the air (car, plane, etc.), which is characterized by a drag coefficient, the surface area of the body (frontal), the square of the speed of this body and the air density .
Dissipative forces are ...
In most cases, mechanical energy passes precisely into heat. Therefore, sliding friction forces serve as the main example. Air resistance and viscous or dry friction are also examples. Most of the systems around us are dissipative. Therefore, it is important to know what dissipative forces are, their examples.