Summary of physics knowledge points in grade three

Deformation of Remarks Formula of Physical Quantity (Unit) Formula

Speed V(m/S) v= S: distance /t: time.

Gravity G (N) G=mg m: mass g: 9.8n/kg or 10N/kg.

Density ρ (kg/m3) ρ=m/V m: mass v: volume.

The resultant force f and (n) are in the same direction: f and =F 1+F2.

Opposite direction: f = f1-when F2 is opposite, f1> Second generation

Buoyancy f float

(N) F float =G object-G sight G sight: the gravity of an object in a liquid.

Buoyancy f float

(n) The formula f float = g object is only applicable.

Objects float or suspend.

Buoyancy f float

(n) f float = g row = m row g = ρ liquid gv row: the gravity of the liquid shifts.

Line m: mass of displacement liquid.

ρ liquid: density of liquid

The fifth line: the volume of liquid discharged.

(i.e. the volume immersed in liquid)

Lever balance condition f1L 1 = f2l2f1:power l1:power arm.

F2: resistance L2: resistance arm

Crown block F=G object

S=h F: tension at the free end of the rope.

G object: the gravity of the object.

S: the distance that the free end of the rope moves.

H: the rising distance of the object.

Moving pulley F= (G object +G wheel)

S=2 h G object: the gravity of the object

G wheel: the gravity of the moving pulley.

Pulley block F= (G object +G wheel)

S=n h n: the number of rope segments passing through the moving pulley.

Mechanical work w

(J) W=Fs F: force

S: distance moved in the direction of force.

effective work

Total work w total w has =G substance h

W total =Fs is suitable for the case that the pulley block is placed vertically.

Mechanical efficiency η= × 100%

Power supply p

(w) P=

Woman: Work.

T: time

Pressure p

(Pa) P=

pressure

stressed zone

Liquid pressure p

(pa) p = rhogh rho: liquid density.

H: depth (from liquid level to required point)

Vertical distance)

Physical quantity unit formula

Name symbol name symbol

Mass m kg kg m=pv

Temperature t celsius c

Speed v m/sec m/sec v = sec/sec

Density p kg/m? kg/m？ p=m/v

Force (gravity) f Newton (cattle) N G=mg

Pressure p Pascal (Pa) Pa P=F/S

Work w joule (coke) J W=Fs

Power p watt (watt) w P=W/t

Current I Ampere (A) A I = U/R.

Voltage u volts (volts) V U=IR.

Resistance r ohm (ohm) r = u/i.

Electric power watt Joule (joule) watt =UIt

Electric power p watt (W) w P=W/t=UI.

Heat q joule (coke) j q = cm (t-t)

Specific heat c coke/(kg c) j/ (kg c)

The speed of light in vacuum is 3x108m/s.

9.8 N/kg

15 C the speed of sound in the air is 340 m/s.

Branch of thermal science

1, endothermic: q endothermic = cm (t-t0) = cm δ t.

2. heat release: q = cm (t0-t) = cm δ t.

3. calorific value: q = q/m

4. Efficiency of furnace and heat engine: η = q effective utilization rate /Q fuel.

5. thermal balance equation: q- discharge = q- suction.

6. Thermodynamic temperature: t = t+273 K.

Department of electricity

1, current intensity: I = Q power /t

2. Resistance: R=ρL/S

3. ohm's law: I = u/r

4, Joule's law:

(1), q = i2rt general formula)

(2), Q = UIT = PT = UQ power = U2t/r (pure resistance formula)

5, series circuit:

( 1)、I=I 1=I2

(2)、U=U 1+U2

(3)、R=R 1+R2

(4)u 1/U2 = r 1/R2 (partial pressure formula)

(5)、P 1/P2=R 1/R2

6, parallel circuit:

( 1)、I=I 1+I2

(2)、U=U 1=U2

(3)、 1/R = 1/R 1+ 1/R2[R = R 1r 2/(R 1+R2)]

(4)I 1/I2 = R2/r 1 (shunt formula)

(5)、P 1/P2=R2/R 1

7 Fixed value resistance:

( 1)、I 1/I2=U 1/U2

(2)、P 1/P2=I 12/I22

(3)、P 1/P2=U 12/U22

8 electricity:

(1), w = UIT = PT = UQ (general formula)

(2), w = i2rt = u2t/r (pure resistance formula)

9 electricity:

(1), p = w/t = ui (general formula)

(2), P = I2r = U2/r (pure resistance formula)

All the physical formulas below 8th grade

V line ÷V object =P object ÷P liquid (f floating =G)

V Lou ÷V Pai =P liquid -P substance ÷P substance.

V dew point ÷V object =P liquid -P object ÷P liquid.

When line V =V object, G÷F float =P object ÷P liquid.

Table of physical theorems, laws and formulas

First, the motion of the particle (1)- linear motion

1) moving in a straight line at a uniform speed

1. average speed Vping = s/t (definition) 2. Useful inference VT2-VO2 = 2as.

3. Intermediate speed vt/2 = Vping = (vt+VO)/2 4. Final speed vt = VO+AT.

5. Intermediate position speed vs/2 = [(VO2+VT2)/2] 1/26. Displacement S = V level T = VOT+AT2/2 = vt/2t.

7. Acceleration A =(vt-Vo)/t {With Vo as the positive direction, A and Vo are in the same direction (accelerating) a>0; On the other hand, a < 0}

8. It is inferred experimentally that δs = at2 {δs is the displacement difference of continuous adjacent equal time (t)}

9. Main physical quantity and unit: initial velocity (VO): m/s; Acceleration (a): m/s2; Terminal speed (vt): m/s; Time (t) seconds (s); Displacement (s): m; Distance: meters; Speed unit conversion:1m/s = 3.6km/h.

note:

(1) The average speed is a vector;

(2) When the speed of the object is high, the acceleration is not necessarily high;

(3)a=(Vt-Vo)/t is only a measure, not a judgment;

(4) Other related contents: particle, displacement and distance, reference system, time and moment [see Volume I P 19]/S-T diagram, V-T diagram/speed and speed, instantaneous speed [see Volume I P24].

2) Free falling body movement

1. Initial velocity VO = 0 2. Final speed VT = GT.

3. Falling height H = GT2/2 (calculated downward from Vo position) 4. Inference Vt2=2gh.

note:

(1) Free falling body is a uniformly accelerated linear motion with zero initial velocity, which follows the law of uniformly variable linear motion.

(2) A = G = 9.8m/S2 ≈ 10m/S2 (the gravity acceleration near the equator is small, and the mountain is smaller than the flat, and the direction is vertical downward).

(3) Vertical throwing.

1. Displacement S = VOT-GT2/22. The final speed vt = VO-gt (g = 9.8m /S2 ≈10m/S2).

3. Useful inference VT2-VO2 =-2G4. Maximum lifting height hm = VO2/2g (from the throwing point)

5. Round trip time t = 2vo/g (time from throwing back to original position)

note:

(1) whole process: it is a straight line motion with uniform deceleration, with positive upward direction and negative acceleration;

I. Measurement

1. length l: main unit: meter; Measuring tool: scale; When measuring, it is necessary to estimate the next bit of the minimum scale; The unit of light years is the unit of length.

Time t: primary unit: seconds; Measuring tools: clocks and watches; Stopwatch is used in the laboratory. 1 = 3600 seconds, 1 second = 1000 milliseconds.

3. mass m: the amount of matter contained in an object is called mass. Main unit: kg; Measuring tool: scale; Tray balance for laboratory use.

Second, the mechanical movement

1. Mechanical motion: the motion of changing the position of an object.

Reference: To judge the motion of an object, another object must be selected as the standard, and the object selected as the standard is called the reference.

3. Uniform linear motion:

① Two methods to compare the speed of movement: A Compare the distance traveled in the same time. Compare the time required to drive the same distance.

② formula:1m/s = 3.6km/h.

Third, force.

Force F: Force is the action of an object on an object. The forces between objects always interact.

Unit of force: Newton (n). Instruments for measuring force: dynamometer; Spring scales are used in laboratories.

The function of force: to deform an object or change its motion state.

The change of the motion state of an object refers to the change of the speed or direction of the object.

The three elements of force: the size, direction and action point of force are called the three elements of force.

The diagram of force should be proportional; Schematic diagram of forces, not to scale.

3. Gravity G: the force exerted on an object due to the attraction of the earth. Direction: vertical downward.

The relationship between gravity and mass: g = mg m = g/g.

G=9.8 N/kg. Reading: 9.8 N/kg, that is to say, the weight of an object with a mass of 1 kg is 9.8 N. ..

Center of gravity: the point of action of gravity is called the center of gravity of an object. The center of gravity of a regular object is in the geometric center of the object.

2. Two-force balance condition: acting on the same object; These two forces are equal in magnitude and opposite in direction; Linear motion.

Under the balance of two forces, an object can be at rest or move in a straight line at a uniform speed.

The equilibrium state of an object means that the object is in a state of static or uniform linear motion. The resultant force of external forces on an object in equilibrium is zero.

5. Synthesis of two forces on the same line: same direction: resultant force f = f1+F2; The direction of resultant force is the same as that of F 1 and F2;

Opposite directions: the resultant force F=F 1-F2, and the resultant force direction is the same as the strong force direction.

Under the same conditions, rolling friction is much smaller than sliding friction.

Sliding friction is related to positive pressure, material characteristics and contact surface roughness. Sliding friction, rolling friction and static friction.

7. Newton's first law, also known as the law of inertia, means that all objects are always in a state of static or uniform linear motion when they are not affected by external forces. Inertia: The property that an object maintains its original static or uniform linear motion is called inertia.

Fourth, density.

⒈ Density ρ: the mass per unit volume of a substance, and density is a characteristic of the substance.

Formula: m=ρV International unit: kg/m3, common unit: g/cm3,

Relationship:1g/cm3 =1x103kg/m3; ρ water =/kloc-0 /×103kg/m3;

Reading: per cubic meter 103kg, which means that the mass of 1 cubic meter of water is 103kg.

1. Density measurement: measure the mass with a pallet balance, and measure the volume of solid or liquid with a measuring cylinder.

Area unit conversion:

1 cm2 = 1× 10-4 m2，

1 mm2 = 1× 10-6mm 2。

Verb (short for verb) pressure

1. pressure p: the pressure per unit area of an object is called pressure.

Pressure f: the force acting vertically on the surface of an object, in N. ..

The function of pressure is expressed by pressure, which is related to pressure and stress area.

Pressure unit: n/m2; Technical name: Pascal (Pa)

Formula: F=PS S: stress area, the common part of two objects in contact; Unit: square meters.

Methods of changing pressure: ① reducing pressure or increasing stress area can reduce pressure; ② Increasing the pressure or decreasing the stress area can increase the pressure.

1. liquid internal pressure: measure the liquid internal pressure: use a liquid manometer (u-tube manometer).

Reason: Because the liquid has gravity, it exerts pressure on the bottom of the container; Due to the fluidity of the liquid, pressure is generated on the wall of the device.

Law: ① At the same depth, the pressure in all directions is equal; ② The greater the depth, the greater the pressure; ③ Different liquids at the same depth, the higher the liquid density, the greater the pressure. [Depth h, the vertical height from the liquid surface to a certain point of the liquid. ]

Formula: p = rhogh h: unit: meter; ρ: kg/m3; G=9.8 N/kg.

13. Atmospheric pressure: gravity produces atmospheric pressure, which proves the existence of atmospheric pressure and is very large. It was the Madeborg Hemisphere Experiment and Torricelli (an Italian scientist) who measured the atmospheric pressure. After the Torricelli tube is tilted, the height of the mercury column remains unchanged and the length becomes longer.

1 standard atmospheric pressure = 76 cm mercury column height =1.01×105pa =10.336m water column height.

Instruments for measuring atmospheric pressure: barometer (mercury barometer, box barometer).

The law of atmospheric pressure changing with altitude: the higher the altitude, the smaller the pressure, that is, the lower the boiling point with the elevation.

Six, buoyancy

1. Buoyancy and its causes: An object immersed in liquid (or gas) is called buoyancy when it is pushed upward by liquid (or gas). Direction: vertically upward; Cause: the pressure difference between liquid and object.

2. Archimedes principle: An object immersed in a liquid is subjected to upward buoyancy, and the buoyancy is equal to the gravity when the object displaces the liquid.

That is, f float = G liquid discharge = ρ liquid gV discharge. (Line V represents the volume of liquid discharged by the object)

3. Buoyancy calculation formula: F float = G-T = ρ gV drainage = F up-down pressure difference.

4. When the object floats: F float = G object and ρ object.

When the object floats: f floats >; G and ρ < ρ liquid when the object sinks: ρ liquid when F floats.

Seven, simple machinery

1. Lever balance condition: f 1L 1 = f2l2. Force arm: the vertical distance from the fulcrum to the line of force action.

The purpose of keeping the lever in the water position by adjusting the nuts at both ends of the lever is to facilitate the direct measurement of the length of the power arm and the resistance arm.

Crown block: equivalent to an arm. It can't save energy, but it can change the direction of force.

Moving pulley: it is equivalent to a lever with twice the power arm as the resistance arm, which can save half of the force, but cannot change the direction of the force.

Work: two necessary factors: ① the force acting on the object; ② The passing distance of the object in the direction of force. W = W unit =FS Work: Joule.

3. Power: the work done by an object in unit time. A physical quantity indicating the speed at which an object does work, that is, an object with high power does work quickly.

W = pt unit p: watt; Unit of w: joule; Unit of t: seconds.

Eight, thermal energy:

1. temperature t: indicates the degree of heat and cold of the object. It is a state quantity.

Principle of common thermometer: According to the characteristics of liquid expanding when heated and contracting when cooled.

The differences between thermometers and thermometers are: ① range, ② minimum scale, ③ glass bulb, curved thin tube and ④ usage.

2. Heat transfer conditions: temperature difference. Heat: the heat absorbed or released by an object during heat transfer. This is a process quantity.

There are three ways of heat transfer: conduction (heat is transferred along an object), convection (heat is realized by the flow of liquid or gas) and radiation (heat is directly emitted from a high-temperature object).

3. Vaporization: the phenomenon that a substance changes from a liquid state to a gas state. Mode: evaporation and boiling, evaporation should absorb heat.

The factors that affect the evaporation rate are: ① liquid temperature, ② liquid surface area and ③ air flow on the liquid surface. Evaporation has a cooling effect.

1. specific heat capacity c: the heat absorbed by a substance with unit mass when the temperature rises by 65438 0℃ is called the specific heat capacity of the substance.

Specific heat capacity is one of the characteristics of matter, and the unit is coke/(kg℃). The specific heat capacity of water in common substances is the largest.

C water = 4.2× 103 joules/(kg℃), reading: 4.2× 103 joules per kg℃.

Physical meaning: The mass of water is 1 kg, the temperature of water rises 1℃, and the absorbed heat is 4.2× 103 Joule.

⒌ Thermal calculation: Q discharge = cm ⊿ t q decrease and intake = cm ⊿ t liter.

Q is directly proportional to c, m and ⊿t, and inversely proportional to c, m and ⊿ t ⊿ t = q/cm.

6. Internal energy: the sum of kinetic energy and molecular potential energy of all molecules in an object. All objects have internal energy. Internal energy unit: Joule

The internal energy of an object is related to its temperature. When the temperature of an object increases, the internal energy increases; When the temperature decreases, the internal energy decreases.

Methods of changing the internal energy of an object: work and heat transfer (equivalent to changing the internal energy of an object)

7. Law of energy transformation and conservation: energy will neither be generated out of thin air nor disappear out of thin air, but will only be transformed from one form to another, or transferred from one object to another, and the total amount of energy will remain unchanged.

Nine, the circuit

The circuit consists of power supply, electric key, electrical appliances, wires and other components. In order to have a continuous current in the circuit, there must be a power supply in the circuit and the circuit should be closed. The circuit has the phenomena of access, open circuit (open circuit), short circuit of power supply and electrical appliances.

2. A substance that conducts electricity easily is called a conductor. Such as aqueous solutions of metals, acids, bases and salts. Substances that do not conduct electricity easily are called insulators. Such as wood and glass.

Under certain conditions, an insulator can become a conductor.

3. Identification of series-parallel circuits: series: current does not bifurcate, parallel: current bifurcates.

The method of converting non-standard circuit diagram into standard circuit diagram: current flow path method is adopted.

Electric energy

1. Electric work W: The work done by current is called electric work. The process of electric current doing work is the process of converting electric energy into other forms of energy.

Formula: w = uqw = UIT = U2t/r = I2RTW = Pt Unit: W Joule, U Volt, I Ampere, T Seconds, Q Library, P Watt.

3. Electric power P: the electric work done by the current in unit time, indicating the speed at which the current does work. Electrical appliances with large electric power can do work quickly with current.

Formula: P = W/T P = UI (P = U2/R P = I2r) Unit: W Joule, U Volt, I Ampere, T Seconds, Q Library, P Watt.

13. Electric energy meter (watt-hour meter): an instrument for measuring the power consumption of electrical appliances. 1 kwh = 1 kwh = 1000 watts× 3600 seconds =3.6× 106 joules.

XI。 attraction

1. Magnets repel magnetic poles with the same name and attract magnetic poles with different names.

The property that an object can attract substances such as iron, cobalt and nickel is called magnetism. A substance with magnetism is called a magnet. The poles of magnets always appear in pairs.

2. Magnetic field: There is an area around the magnet that acts on other magnets.

The basic property of magnetic field is to generate magnetic force to the magnet put in it.

Magnetic field direction: When the small magnetic needle is at rest, the direction pointed by the N pole is the magnetic field direction of this point. The magnetic field around the magnet is represented by magnetic induction lines.

The geomagnetic north pole is near the geographical south pole, and the geomagnetic south pole is near the geographical north pole.

3. Magnetic field of current: Oster experiment shows that there is a magnetic field around the current.

The energized solenoid is equivalent to a bar magnet.

The relationship between the direction of current in the energized solenoid and the polarity at both ends of the solenoid can be judged by the right-hand spiral rule.

(2) subsection treatment: the upward movement is a straight line movement with uniform deceleration, and the downward movement is a free fall, which is symmetrical;

(3) The process of ascending and descending is symmetrical, for example, at the same point, the speed is equal and the direction is opposite.

1) ordinary force

1. Gravity G = mg (vertical downward direction, G = 9.8m/S2 ≈ 10m/S2, the point of action is at the center of gravity, which is applicable to the vicinity of the earth's surface).

Hooke's law f = kx {direction is along the direction of recovery deformation, k: stiffness coefficient (N/m), x: deformation variable (m)}

3. Sliding friction force f =μFN {opposite to the relative motion direction of the object, μ: friction coefficient, FN: positive pressure (n)}

4. Static friction force 0≤f Static ≤fm (contrary to the relative motion trend of objects, fm is the maximum static friction force)

5. Gravity F = GM1m2/R2 (g = 6.67×10-11n? M2/kg2, the direction is on their connection)

6. Electrostatic force F = kq1Q2/R2 (k = 9.0×109N? M2/C2, the direction is on their connecting line)

7. electric field force f = eq (e: field strength N/C, q: electric quantity c, the electric field force applied to the positive charge is in the same direction as the field strength).

8. Ampere force f = bilsin θ (θ is the angle between b and l, when L⊥B: f = Bil, when B//L: f = 0).

9. Lorentz force f = qvbin θ (θ is the included angle between B and V, when V⊥B: f = qvb, when V//B: f = 0).

note:

(1) The stiffness coefficient k is determined by the spring itself;

(2) The friction coefficient μ has nothing to do with pressure and contact area, but is determined by the material characteristics and surface conditions of the contact surface.

(3)fm is slightly larger than μFN, which is generally considered as FM ≈ μ fn;

(4) Other related contents: static friction (magnitude and direction) [see P8]; In the first volume];

(5) Symbol and unit of physical quantity B: magnetic induction intensity (T), L: effective length (M), I: current intensity (A), V: charged particle velocity (m/s), Q: charged particle (charged body) electric quantity (C);

(6) The directions of Ampere force and Lorentz force are determined by the left-hand rule.

2) Composition and decomposition of force

1. The resultant force on the same straight line has the same direction: f = f 1+F2, and the opposite direction: f = f 1-F2 (f 1 > F2).

2. Composition of mutually angled forces:

When f = (f12+f22+2f1f2cos α)1/2 (cosine theorem) f1⊥ F2: f = (f12+f22)/kloc.

3. resultant force range: | f1-F2 |≤ f≤| f1+F2 |

4. Orthogonal decomposition of force: FX = FCOS β, FY = FSIN β (β is the included angle between the resultant force and the X axis TG β = FY/FX).

note:

The synthesis and decomposition of (1) force (vector) follow the parallelogram law;

(2) The relationship between resultant force and components is equivalent substitution, and resultant force can be used to replace the * * * interaction of components, and vice versa;

(3) In addition to the formula method, it can also be solved by drawing method. At this time, we must choose the scale and draw strictly;

(4) When the values of F 1 and F2 are constant, the greater the included angle (α angle) of F 1 and F2, the smaller the resultant force;

(5) The combination of forces on the same straight line can be taken along the positive direction of the straight line, and the direction of forces is represented by symbols, which is simplified as algebraic operation.

Four. Dynamics (motion and force)

1. Newton's First Law of Motion (Law of Inertia): An object has inertia and always maintains a uniform linear motion state or a static state until an external force forces it to change this state.

2. Newton's second law of motion: f = ma or a = f/ma (determined by external force and consistent with the direction of external force)

3. Newton's third law of motion: f =-F' (the negative sign indicates that the directions are opposite, and f and f' interact, and the balance force is different from the reaction force. Practical application: recoil movement).

4. The balance f of * * * point force is equal to 0, which summarizes the {orthogonal decomposition method and the intersection principle of three forces}.

5. Overweight: FN>g, weightlessness: fn

6. Applicable conditions of Newton's law of motion: it is suitable for solving low-speed motion problems, for macroscopic objects, for dealing with high-speed problems, and for microscopic particles [see Volume I, P67].

Note: the equilibrium state means that the object is at rest or moving in a straight line at a uniform speed, or rotating at a uniform speed.

Verb (abbreviation of verb) vibration and wave (mechanical vibration and propagation of mechanical vibration)

1. Simple harmonic vibration f =-kx {f: restoring force, k: proportional coefficient, x: displacement, and the negative sign indicates that the direction of f is always opposite to x}

2. The period of a simple pendulum t = 2π (l/g) 1/2 {l: pendulum length (m), g: local gravity acceleration value, provided that the pendulum angle θ.

3. Forced vibration frequency characteristics: F = F driving force

4. Conditions for occurrence of * * * vibration: F driving force = F solid, A = Max * * * Prevention and application of vibration [see Volume I, P 175].

5. Mechanical waves, shear waves and longitudinal waves [see P2 Volume II]

6. Wave velocity v = s/t =λf =λ/t {In the process of wave propagation, one period propagates forward by one wavelength; The wave velocity is determined by the medium itself.

7. Sound wave velocity (in air) 0℃; 332 m/s; 20℃； 344 m/s; 30℃； 349 m/s; (Sound waves are longitudinal waves)

8. Conditions for obvious diffraction of waves (waves continue to propagate around obstacles or holes): the size of obstacles or holes is less than the wavelength, or there is little difference.

9. Interference conditions of waves: the two waves have the same frequency (constant phase difference, similar amplitude and the same vibration direction).

10. Doppler effect: Due to the mutual movement between the wave source and the observer, the transmitting frequency of the wave source is different from the receiving frequency (the receiving frequency increases when they are close to each other, and decreases when they are opposite [see Volume II P2 1]].

3. Content of molecular dynamics theory: Matter is composed of a large number of molecules; A large number of molecules do random thermal motion; There are interactions between molecules.

4. Intermolecular attraction and repulsion (1) r

(2) r = r0, f citation = f repulsion, f molecular force = 0, and e molecular potential energy = =Emin (minimum value).

(3)r & gt； R0，f quote >； F repulsion and f molecular force represent gravity.

(4)r & gt； 10r0, f = F repulsion ≈0, f molecular force ≈0, e molecular potential energy ≈0.

5. The first law of thermodynamics w+q = Δ u {(work and heat transfer, two ways to change the internal energy of an object, the effect is equivalent),

W: the positive work done by the outside world on the object (J), Q: the heat absorbed by the object (J), and δ U: the increased internal energy (J), which involves that the perpetual motion machine of the first kind cannot be built (see Volume II P40).

Nine, the nature of gas

1. State parameters of gas:

Temperature: macroscopically, the degree of heat and cold of an object; Microscopically, it is a sign of the irregular motion intensity of molecules inside an object.

Relationship between thermodynamic temperature and celsius temperature: t = t+273 {t: thermodynamic temperature (k), t: celsius temperature (℃)}

Volume V: the space occupied by gas molecules, and the unit is1m3 =103l =106ml.

Pressure P: In unit area, a large number of gas molecules frequently collide with the impactor wall, resulting in continuous and uniform pressure. The standard atmospheric pressure is1ATM =1.013x105pa = 76cmhg (1pa =1n/m2).

2. Characteristics of gas molecular movement: large intermolecular gap; Except the collision moment, the interaction force is weak; The molecular motion rate is very high.

3. Equation of state of ideal gas: p1v1/t1= p2v2/t2 {PV/t = constant, t is thermodynamic temperature}

1, electric work: The work done by current is called electric work. The process of electric current doing work is the process of converting electric energy into other forms of energy.

Calculation formula: W = UIT = PT = T = I2RT = UQ (where W = T = I2RT is only applicable to pure resistance circuits).

Unit: Joule (j) Common unit kWh1kwh = 3.6×106 j.

Measurement: watt-hour meter (instrument for measuring the power consumption of household appliances)

Connection: ① series connection in the main circuit of the household circuit; ② "1, 3" in "2,4" out; "1, 2" fire "3,4" zero

Parameter: "220V 10A(20A)" means that the electric energy meter should be used in the 220V circuit; The rated current of the watt-hour meter is 10A, and the current cannot exceed 20A. The total power of electrical appliances in the circuit cannot exceed 2200 W；; "50Hz" means that the electric energy meter should be used in the circuit with AC frequency of 50Hz; "3000R/KWh" means that the dial of the electric energy meter rotates 3000 revolutions every time the working circuit consumes 1KWh.

The formula for indirectly measuring electric power by electric energy meter is p = × 3.6× 106 (w).

2. Electric power: Electric power is the work done by current in unit time. Equal to the product of current and voltage. The unit of electric power is watt. Calculation formula: p = w/t = ui = = i2r (where p = = i2r is only applicable to pure resistance circuits).

3. Difference and connection between rated power and actual power: The rated power is determined by the electrical appliance itself, and the actual power is determined by the actual circuit. Connection: p is a real number = () 2p, which can be understood as 1/n when the voltage across the electrical appliance changes to the original 1/n2.

The brightness of a small light bulb is determined by the actual power of the light bulb.

5. Joule's Law: The heat Q generated by the current passing through the conductor is proportional to the square of the current I, the resistance R of the conductor and the electrifying time T.. Calculation formula: Q = I2RT = UIT = T (where Q = UIT = T is only applicable to pure resistance circuits).

6. Electric heater: The main components are heating elements, which are made of materials with high resistance and high melting point. Its principle is the thermal effect of current.

7. Household circuits

8. Electric shock: an injury accident caused by a certain intensity of current passing through the human body.

9. Common sense of safe electricity use: Don't touch the charged body with voltage higher than 36V, and don't get close to the high-voltage charged body. Surface-mounted sockets shall be installed 1.8m higher than the ground, and household appliances such as electric fans and washing machines shall be grounded.

Speed nu = s/t1m/s = 3.6 km/h.

The speed of sound nu = 340m/s.

The speed of light c = 3× 108 m/s.

Density ρ = m/v1g/cm3 =103kg/m3.

Resultant force F = F 1-F2

F = F 1+F2 F 1, F2 is on the same straight line, with opposite directions.

F 1 and F2 are on the same straight line and in the same direction.

Pressure p = F/S

P = rho g h p = f/s is suitable for solids, liquids and gases.

P =ρg h is suitable for vertical solid columns.

P =ρg h can directly calculate the liquid pressure.

1 standard atmospheric pressure = 76 cmHg column =1.01×105pa =10.3m water column.

Buoyancy ① F float = g–f

② Floating and suspending: f floating = g.

(3) F float = G row = ρ liquid g V row

(4) Judging the buoyancy According to the fluctuation (1), it is judged whether the object is buoyed.

(2) Judging the position of an object according to its ups and downs.

In which state?

(3) Find a suitable formula to calculate buoyancy.

Conditions for the ups and downs of an object (premise: the object is immersed in liquid and only subjected to buoyancy and gravity):

①F float > g (ρ liquid > ρ substance) floats to float ②F float =G(ρ liquid = ρ substance) suspends.

③F float < g (ρ liquid