The main concepts of finding work and energy define the formula theorem

The formula for useful work is w=fs=gh (gh is inBevelor in pulleys, f is the force acting on the object, s is the distance the object moves in the direction of this force), the unit of useful work isJoules

Compare the speed of the work.

Method 1: Do the same work, than time. The shorter the time, the faster the work will be done.

Method 2: The time is the same, and the work is done. The more work you do, the faster you do it.

Method 3: The work done and the time are not the same, and the ratio is different. The greater the value of the work time, the faster the work is done.

Analysis of the relationship between useful work, extra work and total work.

1. Re-probe the pulley.

Analyze "useful work", "extra work", and "total work".

The crane lifts the bricks to the roof of the building, in addition to overcoming the gravity of the bricks, it must also need the gravity of the baskets, pulleys and hooks of the garment bricks. In addition, since there is always friction between objects, the crane has to overcome friction to do work while doing work on the bricks. The work done by the crane to lift the bricks is useful work, and the work done to lift the basket, pulley, hook and overcome friction is additional work. The sum of useful work and extra work is called total work.

2. Analyze the "useful work, extra work and total work" by lifting water from the well with a bucket.

When using buckets to lift water from wells, in addition to overcoming the gravity of the water, it is also necessary to do the work of gravity with auxiliary measures such as buckets and ropes that restrain the water. The work done by the water lifted is useful work, and the work done by the wide bi that Tishen Town lifted the bucket is additional work. If a bucket is fished out of a well, then the work done by carrying the bucket is useless, and the work done by lifting the water in the bucket is extra work.

The formula for calculating work is: w=fsWork = force distance, work (w) is equal to the product of force (f) and distance (s) passing through the object in the direction of force.

If a force acts on an object, and the object moves a certain distance in the direction of the force, mechanics says that the force has done work. Even if there is a force, there may be no work. For example, in a uniform circular motion, the centripetal force.

It doesn't work because the kinetic energy of the object in a circular motion is constant. In the same way, a book on the desk, although it is supported by a book on the table, does not work because it is not displaced.

Generally speaking, there are three cases of reactive power: reactive power, active reactive power and vertical reactive power. (Reactive or reactive power.)

Only the distance is moved, but there is no force in the direction of motion, i.e., 0*fs·cos = 0 joules; Reactive: only force, but no movement in the direction of force, f*0scos = 0 joules; Perpendicular reactive: The object is stressed and passes a certain distance, but the two directions are perpendicular to each other, fscos 90° = fs * 0 = 0 joules.

Heat conduction is not considered to be work because the energy is converted into microscopic atomic vibrations instead of macroscopic displacements.

In the International System of Units.

, the unit of work is joules (j). Joule is defined as 1 Newton.

The force that makes the object move one meter is the mechanical work done.

The unit of the same size, n·m, is sometimes used in liters, but usually n·m is used to represent moments to distinguish them from work and energy.

In international units, the unit of work is joule, abbreviated as "joule", the symbol is j, and the unit is j 1j = 1n·m, and was named by the British physicist James Prescott Joule (1818-1889) for his contribution to science.

Non-SI units include erg, feet·pounds, kilowatt-hours (kw·h), and atmospheric pressure.

and horsepower hours (hp·h). However, since the physical quantity of heat energy is the same, the unit of measurement expressed in the form of heat energy occasionally appears, such as calories.

CAL), BTU, etc.

w useful = fs = gh.

1.(Gh is used in an inclined plane or pulley, F is the force acting on the object, S is the distance the object moves in the direction of this force), and the unit of useful work is joules.

2.Other formulas are: w useful = w total - w amount = w total.

3.Work is the process by which energy is transformed from one form to another. There are two necessary factors for work to be done: the force acting on the object and the distance the object passes in the direction of the force.

4.Definition of classical mechanics: When a force acts on an object and causes the object to pass a distance in the direction of the force, it is said that the force has done work on the object.

Useful work is the part of the work that people do that is useful to people. Useful work refers to the work that is valuable to people in rolling holes.

w=fscos (in the junior high school stage, the angle between the direction of force and the direction of displacement is 0, i.e. =0°, cos0°=1, so w=fs).

Work is the process by which energy is transformed from one form to another.

Two factors that do work:

1. The force acting on the object.

2. The distance the object moves in the direction of this force.

Note: The formula for work can only calculate the work done by a force or a resultant force, and if you want to calculate the total work, you need to use the formula of velocity and mass.

In addition, the different forms of energy in nature correspond to different forms of motion: the motion of objects has mechanical energy, the motion of molecules has internal energy, the motion of electric charges has electrical energy, the movement inside the nucleus of an atom has atomic energy, and so on.

There are three ways to compare the speed of the work.

Method 1: Do the same work, than time. The shorter the time, the faster the work will be done.

Method 2: The time is the same, and the work is done. The more work you do, the faster you do it.

Method 3: The work done and the time are not the same, and the ratio is different. The greater the value of the work time, the faster the work is done.

The formula for work and energy (work is a measure of energy conversion):

1.work: w=fscos (defined) w=fs;

2.Gravitational work: wab=mghab ;

3.Electric field force work: wab=quab ;

4.Electric work: w=uit (universal formula);

5.Power: p=w t (defined);

6.The power of the traction force of the car: p=fv; P-Ping = Fv P-Ping ;

7.The car starts with constant repentant power, starts with constant acceleration, and the maximum driving speed of the car (vmax=p f);

8.Electrical power: p=ui (ubiquitous).

9.Joule's law: q=i 2rt ;

10.In a pure resistive circuit, i=u r; p=ui=u^2/r=i^2r；q=w=uit=u^2t/r=i^2rt

11.Kinetic energy: ek=mv22;

12.Gravitational potential energy: ep=mgh ;

13.Electric potential energy: ea=q a ;

14.Kinetic energy theorem (positive work done on an object, the kinetic energy of an object increases):

W = MVT 2 2-mV0 square 2 or W = δek

w: the total work done by an external force on an object, δek: change in kinetic energy δek = (mvt 2 2 - mvo 2 2)}

15.The law of conservation of mechanical energy: δe=0 or ek1+ep1=ek2+ep2 can also be mv1 2 2+mgh1=mv2 2 2+mgh2;

16.The change in the work done by gravity and the potential energy of gravity (the work done by gravity is equal to the negative value of the increment of the potential energy of the gravitational hand of the object) wg=-δep

Note: 1) The power indicates the speed of the work, and the amount of work done indicates the amount of energy conversion;

2)o0≤α

The formula for work and energy (work is a measure of energy conversion):

1.work: w=fscos (defined) w=fs;

2.Gravitational work: wab=mghab ;

3.Electric field force work: wab=quab ;

4.Electric work: w=uit (universal formula);

5.Power: p=w t (defined);

6.The power of the traction force of the car: p=fv; P-Ping = Fv P-Ping ;

7.The car starts at constant power, starts with constant acceleration, and the maximum speed of the car (vmax=p f);

8.Electrical power: p=ui (ubiquitous).

9.Joule's law: q=i 2rt ;

10.In a pure resistive circuit, i=u r; p=ui=u^2/r=i^2r；q=w=uit=u^2t/r=i^2rt

11.Kinetic energy: ek=mv22;

12.Gravitational potential energy: ep=mgh ;

13.Electric potential energy: ea=q a ;

14.Kinetic energy theorem (positive work done on an object, the kinetic energy of an object increases):

W = MVT 2 2-mV0 square 2 or W = δek

15.The law of conservation of mechanical energy: δe=0 or ek1+ep1=ek2+ep2 can also be mv1 2 2+mgh1=mv2 2 2+mgh2;

16.The change in the work done by gravity and the potential energy of gravity (the work done by gravity is equal to the negative value of the increase in the potential energy of the gravitational force of the object) wg=-δep.

Note: 1) The power indicates the speed of the work, and the amount of work done indicates the amount of energy conversion;

2) o0 <90o to do positive work; 90o< 180o to do negative work; =90o No work done (no work done when the direction of the force is perpendicular to the direction of displacement (velocity));

3) If gravity (elastic force, electric field force, molecular force) does positive work, the potential energy of gravity (elastic, electrical, molecular) decreases;

4) The work done by gravity and electric field is independent of the path (see two formulas);

5) Conditions for the establishment of conservation of mechanical energy: except for gravity (elastic force), other forces do not do work, but only the transformation between kinetic energy and potential energy;

6) Conversion of other units of energy: 1kWh (degree) =, 1ev=;

7) The elastic potential energy of the spring e=kx2 2, which is related to the stiffness coefficient and deformation.

The formula for work and energy is the same.

w=fs (force multiplied by the distance passed in the direction of the force).

w=gh

1 All w = fs, the key is to understand the physical meaning of w, f, s: f - the force acting on the object; s – the distance the object moves in the direction of the force; w – the work done by force f.

Useful work can be understood as: the work done directly by hand without machinery.

Pull up vertically: w has=gh; Pull along the horizontal: w has = fs) The extra work can be expressed by the difference between the total work and the useful work; Total work can be understood as the work done by human hands when using machinery.

Useful work is the work that we want to do to directly carry (drag, pull) an object. You need to find out the force f used to directly carry (drag, pull) the object from the problem, and then find the distance s s that you need to move the object directly (drag, pull).

The formula for useful work this w has =fs.

Then it is obtained by the mechanical efficiency formula =w and w total.

w has = *w total.

The useful work w=gh when lifting heavy objects, and the useful work w=fs. in the process of overcoming frictional force to do work