The difference between energy, heat and potential energy

The significance of "energy" in physics;

Energy is a quantity that describes a system or process in physics. The energy of a system can be defined as the sum of the work from a certain zero-energy state to the current state of the system. How much energy a system has is not a definite value in physics, it changes with the description of the system. In the process of human life activities, all life activities need energy, such as the synthetic reaction of material metabolism, muscle contraction, gland secretion and so on. And these energies mainly come from food. Nutrients contained in animal and plant foods can be divided into five categories: carbohydrates, lipids, protein, minerals and vitamins, and water is six categories. Among them, carbohydrates, fats and protein can release energy through in vivo oxidation. These three are collectively referred to as "productivity nutrients" or "heat sources".

Usually, the average metabolic capacity of carbohydrate, fat and protein per gram is 4 kilocalories, 9 kilocalories and 4 kilocalories respectively. At the same time, generally speaking, a person's calorie intake is equal to his consumption for 5-7 days.

Excess energy will be stored in the body. The storage form of energy in human body is fat, and the abnormal accumulation of fat in human body will lead to obesity, bring unnecessary burden to the body, and may become a risk factor for degenerative diseases such as cardiovascular disease, some cancers and diabetes.

When the daily energy intake of human body is insufficient, the body will use its own energy reserves and even consume its own tissues to meet the energy demand of life activities. People have been hungry for a long time. In a certain period of time, the body will experience basal metabolism reduction, physical activity reduction and weight loss to reduce energy consumption and make the body adapt to energy intake. At this time, energy metabolism will reach a new low-level balance from negative balance. As a result, children's growth and development are stagnant, adults are emaciated and their working ability is reduced.

Any exercise needs energy. There are many forms of energy, such as photoacoustic thermoelectric, mechanical energy, chemical energy, thermal energy, electrical energy, acoustic energy and so on.

For example, we observe the energy of a solid with a mass of 1kg:

If we are studying classical mechanics and are only interested in its kinetic energy, then its energy is the sum of the work we have added to accelerate it from rest to its current speed.

If we are studying heat and are only interested in its internal energy, then its energy is the sum of the work we have added to heat it from absolute zero to its current temperature.

If we are only interested in the chemical energy contained in physical chemistry, then its energy is the sum of the work we add to its raw materials when synthesizing this solid.

If we are studying atomic physics and are only interested in the atomic energy it contains, then its energy is the sum of the work we have done on it from the state of zero atomic energy to the present state.

Of course, we can also use the opposite method to define the energy contained in this solid, and give two examples:

The internal energy of a solid is the sum of the work released by cooling it to absolute zero.

The atomic energy of a solid is the sum of the work that releases all the atomic energy contained in it.

Wait a minute.

It can be seen that although energy is a very common and basic physical concept, it is also a very abstract and difficult to define physical concept. In fact, physicists didn't really understand the concept of energy until the middle of19th century. Before that, energy was often confused with concepts such as force and momentum. For a time, physicists used a concept called "vitality", which was very similar to energy. It means the force that makes an object lively (moving and warming up). The word energy in English is a combination of two Greek words: ε ν means "being" and ε чο s means "working". Taken together, en-ergi means "extra work".

Introduction to heat

In the process of human life activities, all life activities need energy, such as the synthetic reaction of material metabolism, muscle contraction, gland secretion and so on. And these energies mainly come from food. Nutrients contained in animal and plant foods can be divided into five categories: carbohydrates, lipids, protein, minerals and vitamins, and water is six categories. Among them, carbohydrates, fats and protein can release energy through in vivo oxidation. These three are collectively referred to as "productivity nutrients" or "heat sources".

definition

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potential energy

The energy possessed by an object due to its work is called potential energy.

Because of the interaction between objects, the energy determined by the relative position between objects is called potential energy, also known as potential energy, and potential energy is a state quantity.

Potential energy category

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Potential energy is divided into gravitational potential energy, elastic potential energy, molecular potential energy, electric potential energy and gravitational potential energy.

Gravitational potential energy is the energy possessed by an object due to gravity, and the formula is EP = mg △ H.

Elastic potential energy is the energy possessed by an object due to elastic deformation. The formula is EP = 1/2kx 2.

[Molecular potential energy] is the energy generated by the interaction between molecules, which is divided into repulsion and gravity. It is relatively balanced at the equilibrium position r0, repelled when it is less than the equilibrium position, and attracted when it is greater than the equilibrium position. But at any time, attraction and repulsion coexist.

molecular potential energy

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Because of the interaction between molecules, they have energy related to their relative positions, that is, molecular potential energy. Includes kinetic energy and potential energy of molecules. Every molecule has kinetic energy; There is potential energy between interacting molecules. (But there is no interaction between ideal gas molecules, so there is no molecular potential energy. )

Brief introduction of potential energy

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Also known as "potential energy". The energy determined by the relative position between interacting objects or the relative position between internal parts of objects is called "potential energy". According to the different nature of the action, it can be divided into gravitational potential energy, elastic potential energy, electric potential energy and nuclear potential energy. Potential energy in mechanics includes gravitational potential energy, gravitational potential energy and elastic potential energy. Potential energy is not possessed by a single object, but by interacting objects. When the interaction force is "dissipative force" (such as friction), let an object move from point A (assuming zero potential energy) to point B to overcome it, and do work as W. When the object returns from point B to point A, it cannot do work on the object, so it cannot be said that the object has potential energy because of dissipative force. On the contrary, if the above process is carried out under the action of conservative force, then when the object returns from B to A, the work done by conservative force on the object is exactly equal to W, because the work done by conservative force is only related to the initial and final relative positions of the object. If the object is not acted by other forces, then this work W will make the object gain the same amount of kinetic energy. So we say that an object has potential energy w at point B. In a word, potential energy is measured by the work done by conservative forces between objects in the system. Potential energy is energy belonging to a material system. Generally speaking, the potential energy of an object is actually a short statement. Potential energy is a relative quantity. Choosing different zero points of potential energy, the value of potential energy is generally different.

Gravitational potential energy

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The energy that an object has because it is lifted is called gravitational potential energy. (All lifted objects can do work and have gravitational potential energy) The greater the mass of an object, the higher it is lifted, and the greater the gravitational potential energy.

Elastic potential energy

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The energy possessed by an object due to elastic deformation is called elastic potential energy. All objects with elastic deformation can do work and have elastic potential energy. ) The greater the elastic deformation of an object with elastic deformation, the greater its elastic deformation.

conclusion

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According to the definition, an object can be said to have potential energy as long as it can do work.

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