Summary of high school work and power knowledge points, what are the knowledge points of work and po

Work is also called mechanical work, which is a physical quantity in physics that represents the accumulation of space where the force acts on an object, and work is a scalar quantity, and its magnitude is equal to the scalar product of the force and the displacement of the point of action, and the SI unit is joules.

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 number of power judgment codes is constant, and the shorter the time, the greater the power value.

Knowledge points: 1. Due to inertial motion, although the object has a distance, it is not affected by the force. For example, a wooden block that slides at a uniform speed on a smooth horizontal plane has no force to do work on it due to inertia moving forward and is not subjected to resistance or power in the horizontal direction.

2. The object is subjected to the force but remains at rest and does not pass the distance in the direction of the force. For example, pushing the cart hard, without pushing. In this process, there is a lack of a factor to do work, so the force of the cart does not do work on the cart.

3. The object is affected by the force and also passes the distance, but the direction of the distance of the object is perpendicular to the direction of the force on the object, so this force does not do work on the object.

The conversion point of high school physics public knowledge is knowledge, and in terms of knowledge, it has its own formula set.

The power of the college entrance examination physics test is not very much, and it is still necessary to understand the power formula in the book.

Mechanical force is the interaction between objects.

1.The SI unit of force is Newton, denoted by n;

2.Diagram of force: a directed line segment with an arrow indicates the magnitude, direction, and application point of the force;

3.Schematic diagram of force: the direction of the force is represented by a line segment with an arrow;

4.According to the nature, force can be divided into: gravity, elastic force, friction force, molecular force, electric field force, magnetic field force, nuclear force, etc.;

Gravity: The force experienced by an object due to the attraction of the earth to it;

a.Gravity is not gravitational but a component of gravitational force;

b.The direction of gravity is always straight downwards (perpendicular to horizontal downwards).

c.The instrument used to measure gravity is a spring scale;

d.The center of gravity is the equivalent point of gravity of each part of the object, and only the center of gravity of the object with regular geometric shape and uniform mass distribution is its geometric center.

Elastic force: the force exerted by the deformed object on the object in contact with it in order to restore the deformation;

a.Conditions for the production of elastic force: the two objects are in contact and have deformation; The deformation of the force object produces elastic force;

b.Elastic force includes: support force, pressure, thrust, pull, etc.;

c.The direction of the support force (pressure) is always perpendicular to the contact surface and directed towards the object being supported or compressed; The direction of the pulling force is always along the direction of contraction of the rope;

d.Within the elastic limit, the elastic force is proportional to the deformation; f=kx

Friction: When two objects in contact with each other have relative motion or relative motion tendency, the force that hinders the relative motion of the object is called friction;

a.Conditions for the occurrence of frictional force: object contact, surface roughness, extrusion, relative motion or relative motion tendency; If there is elasticity, there is not necessarily friction, but if there is friction, there must be elasticity between the two things;

b.The direction of friction is opposite to the relative motion (or relative tendency of motion) of the object;

c.The magnitude of the sliding friction fslip = the magnitude of the fn pressure is not necessarily equal to the gravitational force of the object;

d.The magnitude of the static friction force is equal to the external force that causes the object to have a relative tendency to move;

Resultant force and component force: If the effect of several forces on an object is the same as that of a force, then this force is called the resultant force of those forces, and those forces are called the component of this force;

a.The effect of the resultant force is the same as that of the component force;

b.The parallelogram rule is observed between the resultant force and the component force: if two line segments representing the force are used as the borderline to make a parallelogram, then the diagonal line sandwiched between these two sides represents the resultant force of the two forces;

c.The resultant force is greater than or equal to the difference between the two components, and less than or equal to the sum of the two components;

d.When decomposing a force, the force is usually decomposed according to its effect; or decompose the force along the direction of the object's motion (or tendency to move) and its perpendicular direction; (orthogonal decomposition of forces);

Vector vectors: physical quantities (e.g., force, displacement, velocity, acceleration, momentum, impulse) that have both magnitude and direction

Scalar: A force of matter (e.g., time, velocity, work, power, distance, current, magnetic flux, energy) that has no direction of magnitude and no direction

Linear motion. The object is in equilibrium (rest, straight at a constant velocity.)

Power is a physical quantity that reflects the speed of the work done, expressed by p, unit: w (watts) instantaneous power: p = fv (f represents the force in the direction of velocity, v represents the speed) average power:

p=w t (w represents the work done by the force in time t) In electricity: p=ui (applicable in all circuits), p=i 2r (only for pure resistive circuits).

Physical significance.

A physical quantity that indicates how fast or slow the work is done by force.

The physical quantity that defines how much work is done per unit time is called power.

Formula power can be divided into electrical power, power of force, etc. Therefore, the calculation formula is also different. p stands for power, the unit is "watts", abbreviated as "watts", and the symbol is "w".

w stands for work, the unit is "joules", abbreviated as "joules", and the symbol is "j". "t" represents time, the unit is "seconds", and the symbol is "s". Calculation formula for electric power:

p=w t = ui, according to Ohm's law U=IR substituting into P=UI can also obtain: P=i*I*IR=(U*U) r In dynamics: power calculation formula:

p=w t (average power); p=fvcosa (instantaneous power) Since w=f(f force) s(s displacement) (the definition of work), the formula for finding the power can also be derived from p=f·v (when v is the average speed, the power is the average power of the corresponding process, and when v is the instantaneous velocity, the power is the instantaneous power of the corresponding state). 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. Maximum power is generally expressed in horsepower (ps) or kilowatts (kW), and 1 horsepower is equal to kilowatts.

1w=1j/s

1. Significance of matter: Describe the physical quantity of how fast or slow an object does work.

2. Definition: The amount of work done per unit of time.

3. Formula: p=w t (definition).

4. SI unit: watt (w) 1w = 1j s common unit: kilowatt (kw) 1kw = 1000w

5. Average power and instantaneous power.

1) p=w t, p refers to the average power.

2) Instantaneous power: The power at a certain moment. Definition: p= w t, t is very little.

The locomotive has two starting modes.

1.There are two modes of motion in the locomotive starting problem, i.e., the locomotive starts at constant power (usually rated power) and at constant acceleration a.

2.Two basic relationships.

f-f=ma" and "p=fv" are two important and basic relationships for analyzing and dealing with the locomotive starting process. It reflects the relationship between the various quantities of the instantaneous state of the locomotive.

When the rated power is started.

From "f-f=ma" and "p=fv", it can be seen that because the power p remains unchanged and the speed increases, the traction force f of the locomotive will inevitably decrease, and it is not difficult to see that the acceleration a of the locomotive decreases accordingly, so the process is a motion in which the acceleration gradually decreases. Obviously, when the traction force f is reduced to equal to the resistance f experienced by the locomotive, i.e., f = f, and its acceleration a = 0, the speed of the locomotive reaches its maximum value.

The case of a constant acceleration start.

The process of starting with uniform acceleration with an initial velocity of 0 is also known according to "f-f=ma" and "p=fv", because the acceleration a is constant, the traction force f is constant (usually the resistance f of the locomotive is constant). Therefore, with the increase of speed v, the instantaneous power p of the locomotive increases accordingly, and when p increases to the rated power p, the velocity is the maximum speed vm of the uniform acceleration motion process', which is a VM in size'=p Forehead f.

It should be noted that it is the final state of uniform acceleration motion, the power of the locomotive at this moment is just equal to the rated power p, and the traction force is still f at this moment, and f > f, and then by the two basic relations "f-f=ma" and "p=fv", it is easy to analyze that under the condition of constant power, the speed will continue to increase, and the traction force will decrease, so the process thereafter is the acceleration motion of gradually decreasing, until the acceleration a=0, the speed of the locomotive reaches the final maximum speed vm=p f.

Instantaneous power: p=fv (f denotes the force in the direction of velocity, v denotes velocity).

Average power: p=w t (w represents the work done by the force in time t).

Power is a physical quantity that reflects how fast an object does work. Units: Watts.

p=fv, p=w t, one instantaneous power, one average power.