What is Electrical Mechanical Energy?

Mechanical energy is the sum of kinetic energy and potential energy. The potential energy here is divided into gravity potential energy and elastic potential energy. We call kinetic energy, gravity potential energy, and elastic potential energy collectively mechanical energy. What determines kinetic energy is mass and velocity; what determines gravity potential energy is mass and height; what determines elastic potential energy is stiffness coefficient and deformation. Mechanical energy is just the sum of kinetic and potential energy. Mechanical energy is a physical quantity that indicates the state and height of an object's movement. The kinetic and potential energy of an object can be converted. In the process of only kinetic and potential energy conversion, the total amount of mechanical energy remains unchanged, that is, the mechanical energy is conserved.

Chinese name: Mechanical energy

Foreign name: mechanical energy
Applied discipline: physics

Definition of mechanical energy

Mechanical energy refers to: under the condition of excluding friction and medium resistance, only the mutual conversion of kinetic energy and potential energy occurs and the total amount of mechanical energy remains unchanged, that is, the increase or decrease of kinetic energy is equal to the decrease or increase of potential energy, that is, the law of conservation of mechanical energy. Mechanical energy is related to the mechanical movement of the entire object. When there is friction, part of the mechanical energy is converted into internal energy, which is lost in the air, and the other part is converted into kinetic or potential energy. So there is no conservation of mechanical energy in nature, then the perpetual motion proposed by Leonardo da Vinci cannot be created, that is, there is no perpetual motion.

Kinetic energy unit J (Joule) Definition: The energy that an object has due to its movement.

Mechanical energy

The factors that determine the amount of kinetic energy are the mass and speed of the object.

The wind blows the sailing boat, and the air does work on the sailing boat; the rapid river water flushes the stones away, and the water does the work; Did work. Flowing air and water, moving steel balls, they can do work, they all have energy. Air, water, and steel balls are capable of doing work because of movement. The energy they have is called kinetic energy. All moving objects have kinetic energy. ^[1]

Factors affecting mechanical energy

What factors are related to the amount of kinetic energy?

Experiment: Let the steel ball roll down from the inclined surface and hit a small wooden block.

Push wood blocks to do work. Let the same steel ball roll down from different heights to see which block is pushed far away. Use different quality steel balls, let them roll down from the same height, and see which steel ball pushes the block farther.

The same steel ball, the higher the original position, the higher the speed when rolling to the lower end of the slope, the farther the wooden block is pushed. At the same rolling speed, the greater the mass of the steel ball, the farther the wooden block is pushed.

Mechanical energy experimental results

The experimental results show that the greater the mass of the steel ball falling from the same height, the further the wooden block is pushed, the more work is done on the wooden block; at the same time, the steel ball falls from a higher position when the mass is constant, and the final speed The farther you push the block, the more work you do on the block; this means that the kinetic energy of the steel ball is greater. Therefore, the greater the speed of the moving object, the greater the mass, and the greater the kinetic energy it has.

Experimental method of mechanical energy

(1) Control variable method (2) Conversion method (analog method)

Mechanical energy conclusion

When the objects have the same mass, the faster the object moves, the greater the kinetic energy.

Mechanical energy experiment

When the objects move at the same speed, the greater the mass of the object, the greater the kinetic energy.

In the case of macroscopic low speed, the kinetic energy calculation formula E = 1 / 2mv ^ 2;

Supplementary formula for mechanical energy

Einstein supplemented the above formula in the theory of relativity

The complete formula is

E = m0C ^ 2 / (1-V ^ 2 / C ^ 2) -m0C ^ 2

m0 is the static mass

Kinetic energy

The energy that an object has due to its movement is called kinetic energy, and is usually defined as the work done by an object from a stationary state to a moving state. Its size is one-half of the product of the mass and speed square of the moving object. All moving objects have kinetic energy.

Kinetic energy: Ek = 1 2 · m · v ^ 2

Functional relationship of mechanical energy

Relation between gravity work and gravity potential energy change: WG = -Ep

The relationship between the work of external force and the change of kinetic energy: Whe = Ek

In addition to gravity and system internal force, the relationship between the work done by the force and the change in mechanical energy: W = E

Mechanical potential energy

Potential energy: (gravity potential energy Ep = mgh, elastic potential energy: potential energy due to elastic deformation)

The potential energy of a charged object does not belong to mechanical energy, and you can also use the kinetic energy theorem to do work on the object. If the electric field force does positive work on a charged object, the potential energy decreases and the mechanical energy increases; otherwise the electric field force does negative work on a charged object, the potential energy increases and the mechanical energy decreases.

When people pile a pile, they first lift the weight high, and when the weight falls, they can drive the pile into the ground. The weight is capable of doing work because it is lifted up. The energy that a lifted object has is called the gravitational potential energy. The greater the mass of an object, the higher it lifts, and the greater its gravitational potential energy. The raised hammer has the potential energy of gravity. The greater the mass of the weight, the higher the weight is lifted, and the more work done when falling, the greater the gravitational potential energy of the weight. (Not all lifts are artificial, but the height rising relative to the horizontal plane is the height being lifted)

The archer pulls the bow, and the bow that is bent after letting go can shoot the arrow. The compressed spring can lift the weight pressed on it when it is relaxed. Both bows and springs can work because of elastic deformation. The energy of an elastically deformed object is called elastic potential energy. The greater the elastic deformation of an object, the greater its elastic potential energy.

Kinetic energy and potential energy are collectively called mechanical energy. An object can have both kinetic energy and potential energy. For example, an airplane in flight has kinetic energy because it is in motion, and gravity potential energy because it is at a high place. Adding these two kinds of energy together gives you the total energy. Mechanical energy. Mechanical energy is the most common form of energy.

As mentioned earlier, the more work an object can do, the greater the energy of the object. Therefore, the amount of energy can be measured by the amount of work done. The unit of kinetic energy, potential energy, or mechanical energy is the same as that of work, and it is also Joule. For example, we say that the gravity potential energy of a ball flying in the air is 5 J, the kinetic energy is 4 J, and the mechanical energy of the ball is 9 J.

The shape change of an object under the action of an external force is called deformation. If the external force is withdrawn, the object can return to its original state. This deformation is called elastic deformation.

Conservation of mechanical energy was first proposed by Galileo, who made a bevel experiment. An object sliding on the left end of the bevel would move to the same height at the other end if it was not affected by resistance.

Relationship between mechanical energy potential energy and kinetic energy

The amount of kinetic energy increase is equal to the amount of gravity potential energy decrease

Mechanical energy

The author analyzes and understands the nature of conservation of mechanical energy from the perspective of energy conversion and functional relationship:

Mechanical energy from the perspective of energy conversion

From the perspective of energy conversion, as long as the total amount of mechanical energy of the system remains the same in a certain physical process, and there is no mechanical energy in the system or between the system and the outside world, which is not converted into other forms of energy, The mechanical energy of the system, then the mechanical energy of the system is conserved and has nothing to do with whether the mutual conversion of kinetic energy and potential energy must occur in the system. For example, do an object that moves at a constant linear speed on a smooth horizontal surface. Its mechanical energy is conserved; if there are other forms of energy and mechanical energy conversion within or between the system and the outside world. Even if the total mechanical energy of the system remains unchanged, its mechanical energy is not conserved. For example, when a bomb explodes, it is assumed that external force does not do work, but the chemical energy (non-conservative force) in the system does work on the system. Although the total mechanical energy remains unchanged However, there are other forms of energy (internal energy or electrical energy) in the system that are converted into the mechanical energy of the system, and the system overcomes the external work to convert mechanical energy into other forms of energy.

Mechanical energy

From the perspective of functional relationship, the condition for conservation of mechanical energy is "external force in the system does not do work, and non-conservative forces in the system do not do work". This condition has nothing to do with whether the conservative force (gravity or spring elastic force) in the system does work, because whether gravity or spring elastic force does work only determines whether the mutual conversion of kinetic and potential energy occurs in the system. Whether the work does not change the total mechanical energy of the system .

It can be known that if all the forces (including gravity and elastic force) on the objects in the particle group (system) do not perform work, the kinetic energy and potential energy of each object will remain unchanged, and the kinetic energy and potential energy will not be converted into each other. The mechanical energy of the time particle group (or system) is also conserved. This is a special case of conservation of mechanical energy. For example, an object that makes a circular motion on a smooth circular track on the horizontal plane. Although the track provides a centripetal force that always points to the center of the circle in the horizontal direction, it does not perform work on the object, and its total mechanical energy remains unchanged, so the mechanical energy of the system It is also conserved.

The law of conservation of mechanical energy is expressed as follows: In the case that only gravity does work, the kinetic energy and potential energy of an object are transformed into each other, but the total amount of mechanical energy remains unchanged. This is the most common case of the law of conservation of mechanical energy (that is, in the mutual conversion of gravity potential energy and kinetic energy, only gravity does work. In fact, in the mutual conversion of gravity potential energy and elastic potential energy and kinetic energy, only gravity and spring elastic force do work. At this time, the sum of the kinetic energy of the object and the potential energy of the system remains unchanged, and the mechanical energy of the system is conserved), which is also a special case of the more general law of conservation of mass.

The law of conservation of mechanical energy can be considered as the law of energy conversion and conservation in mechanics. Its condition is that the system only works with gravity and elastic force. In such a system, although kinetic and potential energy are being transformed into each other, the total mechanical energy is constant. Here we talk about the application of the law of conservation of mechanical energy.

First, the conservation of mechanical energy is for the system, not for individual objects. Such as: earth and objects, objects and springs. For the conservation of the mechanical energy of the system, it is necessary to appropriately select the reference frame, because whether the mechanical energy of a mechanical system is conserved is related to the selection of the reference frame.