How physical work and power are represented by symbols

a) Gong 1Work in mechanics aThere are two necessary factors to do work:

1) The force acting on the object. (f) (2) The distance that the object passes in the direction of the force. (s) b.

Examples of non-work are given: (1) The object is not acting on a force, but because of inertia passing a certain distance, i.e., there is no force to do work. For example, on a smooth horizontal ice surface, an object moves in a straight line at a uniform speed due to inertia.

Didn't feel forced. (2) The object is subjected to a force but does not move a distance, i.e., the distance passed is zero. For example, if a person pushes a car with a lot of force, the car does not move, and the thrust does not do work on the object.

3) The object is acted upon by the force and also moves the distance, but the distance moved is not in the direction of the force. For example, if you are walking on a level ground with a bucket of water, the force of the bucket does not exert force on the bucket. 2.

Computational of Work Work in mechanics consists of two necessary factors, work is equal to the product of the force and the distance that the object travels in the direction of the force. (1) Formula for calculating work: w=fs (2) Unit of work:

Joule J, 1 joule = 1 N 6 1 m. Physical meaning of joules: The distance that an object passes in the direction of this force under the action of 1 Newton force is 1 meter.

Does it save effort with movable pulleys? The facts show that when using machinery, people do no less work than when they don't use machinery, that is, they don't save work when they use any machinery, and this conclusion is called the principle of work.

2) Power **Animation: Power The concept of power is derived from comparing the speed of workmanship of people and excavators. Or create a situation where student A takes 30 seconds to lift a bucket of water to the third floor, and student B takes 40 seconds to lift the same bucket of water to the third floor.

If object A does 300 j of work in 1 minute, and object B does 240 j of work in 40 seconds, who does the work fast? Thus, it is proposed that the speed of the work done by the object is expressed by power to introduce a new lesson. Select the button for the corresponding content in the animation to learn.

1 Power is a physical quantity that indicates how fast or slow an object does work. 2 Definition of power: The work done per unit of time is called power.

3 Definition of power: p=w t 4 Units of power: watts (symbol w) 1 watt = 1 joule; 1 kW = 1000 watts.

5 Physical Significance: 1 watt means that the work done by an object in one second is 1 joule. 6 Introducing another unit of power:

1 horsepower = kW = 735 watts. 7 The power common in some machinery 8 Shao rated power (power on the nameplate). 3. Summary In this lesson, we learned about work and power, and also learned to calculate work and power.

Work is the product of the distance traveled in the direction of the force and force, and power is the work done per unit of time. Calculation of work in work mechanics: w=fs principle of work:

It is not easy to use any machinery. Power p=w t

1. ElectricityPower calculation formula：p=w/t =ui。

in purely resistive circuits.

, according to Ohm's law.

U=IR can also be substituted into P=UI to get P=I2R=(U2) R.

Second, in dynamics, the power calculation formula is accompanied by a loud voice:

1. P=W t (average power).

2、p=fv；p=fvcos (instantaneous power).

Since w=f(f) s(s displacement) (the definition of work), the formula for finding power can also be derived from p=f·v.

P in the formula stands for power, the unit is "watts", abbreviated as "watts", and the symbol is w.

w denotes work. The unit is "joules", abbreviated as "joules", and the symbol is j.

t is the time, the unit is "seconds", and the symbol is"s"。

Notes:

The currents are equal everywhere: i1 = i2 = i.

The total voltage is equal to the sum of the voltages at both ends of each electrical appliance: u=u1+u2.

The total resistance is equal to the sum of the resistances: r=r1+r2.

The ratio of the voltage at both ends of the electrical appliance in the circuit is equal to the ratio of resistance: u1:u2=r1:r2.

The total electrical work is equal to the sum of the electrical work: w=w1+w2.

The ratio of each electrical work is equal to the ratio of resistance to the ratio of terminal voltage: w1:w2=r1:r2=u1:u2.

The symbol for current is i, the sign for voltage is u, and the symbol for power is p.

Current (i) Scientifically, the amount of electricity passing through any cross-section of a conductor per unit of time is called the current intensity.

Abbreviated as electric current. Usually denoted by the letter i, it is measured in amps.

a）。<

The voltage (u) is also known as the potential difference.

or potential difference, is a physical quantity that measures the energy difference between a unit charge in an electrostatic field due to different potentials. Its magnitude is equal to the work done by a unit positive charge to move from point A to point B due to the action of an electric field force, and the direction of the voltage is specified as the direction from the high potential to the low potential. SI system of units for voltage.

is volts (V, abbreviated as volts).

Power (p) is a physical quantity that describes how fast or slow work is done. The amount of work is constant, and the shorter the time, the greater the power value. The work done per unit of time is called power and is denoted by p.

Power can be divided into electrical power, power of force, etc. Therefore, the calculation formula is also different.

Formula for calculating electrical power.

p=w/t =ui；

In a purely resistive circuit, according to Ohm's law.

U=IR can also be substituted into P=UI to get P=I2R=(U2) R.

In kinetics: power calculation formula: average power); p=fvcos (instantaneous power).

The power symbol is p.

p=w/t=ui；In a purely resistive circuit, according to Ohm's law, U=IR is substituted into P=UI, and P=I2R=(U2) R can also be obtained

In kinetics, the power is calculated as follows: 1, p=w t (average power) 2, p=fv; p=fvcos (instantaneous power).

Power refers to the amount of work done by an object per unit of time, i.e., power is a physical quantity that describes how fast or slow work is done. The amount of work is constant, and the shorter the time, the greater the power value. The formula for finding power is power = work time.

Power indicates the physical quantity of how fast or slow the work is done. The work done per unit of time is called power and is denoted by p. Therefore, the power is equal to the scalar product of the force and the velocity of the point where the object is stressed.

Electricity power and safe use of electricity:

The relationship between electrical power and current, in a home circuit, the voltage U=220V is constant. Since i = p u, the greater the total power p of the appliance, the greater the total current i in the circuit. If the total current in the circuit exceeds the safe value, the fuse is prone to burnout.

Therefore, do not use multiple high-power appliances at the same time in the home circuit.

The relationship between the actual electrical power and the rated electric power of the electrical appliance (U: represents the voltage, P: represents the electrical power):

1. When U actual = U rated, P actual = P rated, the electrical appliance is in normal working condition.

2. When you are actually 3, when you are actually rated and P is rated, the life of electrical appliances is shortened and it is easy to burn out.

w denotes work, and the unit is ".Joules", referred to as "Jiao", and the symbol is "J".

The split spring unit of power is watts (w). International Authorities.

Watt(w); Common units: 1KW=1 103W, 1MW=1 103KW=1 106W, 1HP=735W. The higher the power, the higher the speed, the higher the maximum speed of the car, and the maximum power is often used to describe the power performance of the car.

Power can be divided into electrical power, power of force, etc. Therefore, the calculation formula is also different.

Formula for calculating electrical power.

p=w/t =ui。

In a purely resistive circuit, according to Ohm's law.

U=IR can also be substituted into P=UI to get P=I2R=(U2) R.

In kinetics: power lead hole calculation formula: average power); p=fvcos (instantaneous power).

The symbol for work is j.

International System of Units.

The unit of Zhonggong is Joule Huizhao.

j）。Joule is defined as 1 Newton.

The force on the front of an object causes a displacement of 1 meter to the magnitude of the mechanical work. The same unit of surplus, Niu-meter, is sometimes used, but generally New-meter is used for moment, so that it can be distinguished from work and energy.

In international units, the unit of work is joules, abbreviated as 'joules', with the symbol j, and the unit is j 1j=1n·m, named after the British physicist James Prescott Joule (1818 1889) for his contributions to science.

Three situations of not doing work:

1. The object is subjected to force, but the object does not pass the distance in the direction of the force, which is called "labor without effort".

2. The object has moved a certain distance, but there is no force in this direction of motion (such as the object moving due to inertia), this situation is called "no work".

3. The object is both stressed and passes through a certain distance, but the two directions are perpendicular to each other (such as the crane lifting the goods in the air and moving in the horizontal direction), this situation is called "vertical reactive power".

w。Note that it is not a symbol for the unit of work, the joule, not for the work.

The symbol for electrical work is w.

The amount of work done by the current is related to the size of the current, the level of the voltage, and the length of the energizing time. The higher the voltage applied to the electrical appliance, the greater the current that passes, and the longer the energizing time, the more work is done by the current. The study shows that when the voltage at both ends of the circuit is U, the current in the circuit is I, and the energizing time is T, the electrical work w (or the electrical energy consumed) is:

w=uit。

A large number of test results have proved that under the same power-on time, the larger the voltage pie, the larger the current, and the higher the weight is raised, which means that the dust and silver rubber do more work to do the current. If the voltage and current are kept constant, the longer the energizing time is, the higher the weight is raised, and the more work the current does.

Electrical power. In the same time, the work done by the current through different electrical appliances is generally not the same. For example, in the same amount of time, the work done by the electric motor of an electric current passing through an electric locomotive is significantly greater than that passing through an electric fan.

The work done by the electric motor. In order to represent how fast or slow an electric current does work, the concept of electrical power is introduced into physics.