Give an example of what useless work means?

Inactive work generally refers to extra work.

Extra work is the work that you don't have to do but have to do it, and the extra work plus useful work is the total work.

Useless work: Definition: Work that is not needed but has to be done.

Formula: W = W Total W Useful = G Moving H (Ignoring Wheel Axle Friction Movable Pulley, Pulley Group) Inclined Plane: W Amount = FL

For example, the work done by lifting water from a well with a wheel axle (roller) and the power added to the wheel is the total work, which is equal to f·2 r·n, where f is the power, r is the radius of the wheel, and n is the number of revolutions of the wheel. When water is lifted, the work done on the water is useful work, which is equal to g·h, where g is the weight of water, and h is the height of lifting water.

In order to lift the water up, to use the bucket, it is necessary to do work on the bucket, and the use of the wheel axle also has to overcome the friction force to do the work, these two parts of the work in order to achieve the purpose of lifting water and have to do additional useless work, so it is called extra work.

Useless work is also known as "extra work". It roughly means:

The work that an object does not have to do but has to do.

1. Extra work (useless work) + useful work = total work.

2. (1) Calculation formula: extra work w = w total w has = g motion h (ignoring the friction between the axles) = f (friction) l (inclined plane).

2) Horizontal pulley w = f mos

The extra work can be reduced by reducing friction, etc.

3. Expansion: There are several words that must be noted, "useful", "useless", and "have to". When teaching, it is necessary for students to understand these words, and at the same time, they can analyze them from the purpose of mechanical work.

I picked up a bucket of water and put it on the water dispenser for analysis, and I guided it like this: If the water in the water dispenser is gone, which student can load the bucket of "water" next to it? After the student put it on, I asked again:

But he didn't do what I asked him to do. The students were a little puzzled, and I went on to explain, "My intention was to get this student to carry the water, but he not only carried the water, but also the buckets.

At this time, the students hurriedly explained: "The water must be filled with buckets." "Yes, some of the exercises that this student did just now were for water, and some were for buckets.

From the point of view of the purpose of doing work, the work done by a student on water is 'useful', which is called useful work, while the work done on a bucket is the work that has to be done to achieve the purpose, we call it 'extra work', and 'useful work' plus 'extra work' is the 'total work' done by this student. Then guide the students to analyze the examples of carrying sand in the textbook and ask:

a In the process of transporting sand from the first floor to the third floor, which objects were worked on in each method?

b The work that must be done regardless of the method he takes is the work he does for what?

c What are the different ways in which he is unwilling to do but has to do it?

Students discuss, think, compare, and analyze and conclude that in the above activities, it is our purpose to raise the sand to a certain height, and the work done is useful. The work done by the power on the movable pulley is the total work. When using the movable pulley to lift heavy objects, the work done to overcome friction, and the work done to lift the movable pulley, which is useless to us but have to do is called extra work.

The relationship between the three is: w total = w has + w amount. Of the three methods of sand transportation just listed, which one do you think is the best?

Which method is the worst and why? Combined with experiments, students are guided to analyze the problems of useful work, extra work, and total work, so that students can realize that the work done by power on machinery is total work, the useful work done by machinery on heavy objects is useful work, and the work done by machinery to overcome its own gravity and friction is additional work.

Physical uselessness.

It is useless to do the work, but it is the work that you have to do. For example, when lifting a heavy object with a du pulley, the work done by lifting the heavy object is the useful work of the dao, and in the process of lifting the pulley, it is also necessary to do the work, and this work is useless work.

Useless work in life refers to people who have made efforts without getting any results, reaping any results, and achieving any achievements.

The active power reflects the irreversible part of the power in the energy conversion process of the circuit, and the reactive power reflects the part of the power that is only exchanged and not consumed in the energy conversion process of the circuit.

In the process of generation, transmission and use of alternating current energy, the energy of the department used to convert into non-electric and magnetic forms is called active power.

The energy used for the exchange of electricity and magnetic fields in the circuit is called reactive power.

The difference between "active power" and "reactive power":

Active power (P) refers to the electrical power required to keep the equipment running, that is, the electrical power to convert electrical energy into other forms of energy (mechanical energy, light energy, thermal energy, etc.).

The reactive power (q) refers to the electrical power required to establish a magnetic field when the inductor, capacitor and other components in the electrical equipment are working.

The connection between "active power" and "reactive power":

The equipment needs to be reactive and active during operation, and they need to cooperate with each other to maintain the normal working state of positive dust.

Reactive power: the work that maintains the operation of the equipment, such as generating magnetic fields, etc., this part is not work, so we call it reactive power.

Active effect: the work required to actually produce the product, this part is the consumption of electrical energy to produce the product, so we call it active.

Active power: directly consumes electrical energy, converts electrical energy into mechanical energy, thermal energy, chemical energy or sound energy, and uses these energies to do work, this part of the power is called active power.

Reactive power: Reactive power is used for the exchange of electric field and magnetic field in the circuit, and is used to establish and maintain the electric power of the magnetic field in the electrical equipment. All electrical equipment with electromagnetic coils, the establishment of magnetic field in the sedan car, it is necessary to consume reactive power.

Reactive power does not do work, but to ensure the conduction of active power, it must first meet the reactive power of the power grid.

In physics, the work that has practical value when completing a certain task is called useful work, which is expressed by w have.

For example, the work done on the object of work when working with machinery is called useful work.

Other work that has no practical value and has to be done is called useless work, also known as extra work, and is expressed by w.

For example, when carrying sand upstairs, the work done on buckets, pulleys, etc., is extra work.

The sum of the useful work and the forehead and the external work is called the total work, which is expressed by the total w.

w total = w has + w amount.