To infer, it is similar to 1m / S = 3.6km/h

To infer, it is similar to 1m / S = 3.6km/h

Junior high school physics must remember knowledge
1、 Constants to remember
1. Light (electromagnetic wave) propagates fastest in vacuum, C = 3 × 105 km / S = 3 × 108 M / s. light propagates more slowly in other transparent materials than in air
The speed of sound in air at 15 ℃ is 340m / s, the sound is produced by vibration, the sound transmission needs medium, and the sound cannot be transmitted in vacuum
3. Water density: 1.0 × 103kg / m3 = 1g / cm3 = 1.0kg/dm3
Boiling point of water at 1 standard atmospheric pressure: 100 ℃, melting point of ice: 0 ℃,
The specific heat capacity of water is 4.2 × 103J / (kg ·℃)
4. G = 9.8n/kg, 10 N / kg is recommended for special instructions
5. A standard atmospheric pressure = 76cmhg = = 760mmhg = 1.01 × 105Pa = 10.3M water column
6. Several voltage values: one dry battery 1.5V, one lead-acid battery 2V. The lighting circuit voltage is 220V, and the safety voltage is not higher than 36V
1 degree = 1 kwh = 3.6 × 106j
8. Common low-power electrical appliances: electric lamp, TV, refrigerator, electric fan;
Common high power electrical appliances: air conditioning, induction cooker, electric rice fort, microwave oven, electric iron
2、 International unit of physical quantity
Length (L or s): M
Time (T): seconds (s)
Area (s): M2
Volume (V): M3
Velocity (V): M / S
Temperature (T): centigrade (℃) (this is a common unit)
Mass (m): kg (kg)
Density (ρ): kg / m3 (kg / m3)
Force (f): Newton (n)
Work (energy, electric work, electric energy) (W): Joule (J)
Power (electric power) (P): Watt (W)
Pressure (P): Pascal (PA)
Mechanical efficiency (η)
Heat (electrothermal) (q): Joule (J)
Specific heat capacity (c): Joule / kilogram centigrade (J / kg ℃)
Calorific value (q): J / kg or J / m3
Current (I): Ampere (a)
Voltage (U): volt (V)
Resistance (R): Ohm (Ω)
3、 Unit conversion
1nm=10-9m,
1mm=10-3m,
1cm=10-2m;
1dm=0.1m,
1Km=103m,
1h=3600s,
1min=60s,
1Kwh=3.6×106J.
1Km/h=5/18m/s=1/3.6m/s,
1g/cm3=103Kg/m3,
1cm2=10-4m2,
1cm3=1mL=10-6m3,
1dm3=1L=10-3m3,
Crowns: m (10-3), μ (10-6), K (103), m (106)
4、 Formula
1. Velocity v = s / T;
2. Density ρ = m / V;
3. Pressure P = f / S = ρ GH;
4. Buoyancy f = g row = ρ liquid GV row = g (suspension or floating) = f up-f down = G-F ';
5. Lever balance condition: f1l1 = f2l2;
6. Work w = FS = GH (work against gravity) = Pt;
7. Power P = w / T = FV;
8. Mechanical efficiency η = w / W total = GH / Fs = g / NF = g / (G + G dynamic) = FL / Fs;
9. Heat: heat transfer, heat absorption and release, q = cm △ T; fuel complete combustion, q = MQ = VQ; electric heating, q = i2rt
10. Electrical formula:
Current: I = u / r = P / u
Resistance: r = u / I = U2 / P
Voltage: u = IR = P / I
Electric work: w = Pt = uit = i2rt = u2t / R
Electrothermal: q = i2rt (Joule's law) = uit = = u2t / R
Electric power: P = w / T = UI = I2R = U2 / R
Series circuit features:
I=I1=I2,
U=U1+U2,
R=R1+R2
U1:U2=P1:P2=Q1:Q2=W1:W2=R1:R2
Characteristics of parallel circuit:
I=I1+I2,
U=U1=U2,
1/R=1/R1+1/R2
I1:I2=P1:P2=Q1:Q2=W1:W2=R2:R1
5、 Physicists and their contributions
Name contribution
Ampere: Ampere rule (right hand rule)
Newton (force) the founder of Newton's first law of motion, dispersion and classical physics
Torricelli Torricelli experiment → first measure the value of atmospheric pressure
Sound transmission and magnetic declination of Shen Kuo solid
The magnetic effect of Oster current
Faraday electromagnetic induction phenomenon
Ohm's law
Joule's law
Archimedes Archimedes principle (buoyancy), lever balance principle
Rutherford alpha particle scattering experiment: atomic planet (nuclear) model
6、 Important concepts, laws and theories
1. Remember the names of the six states of matter and whether they are endothermic or exothermic
2. Remember six laws of Physics: (1) Newton's first law (Law of inertia) (2) law of light reflection (3) law of light refraction (4) law of energy conversion and conservation (5) Ohm's Law (6) Joule's law. Remember two principles: (1) Archimedes' principle (2) lever balance principle
3. Mass is an attribute of an object: it does not change with shape, geographical location, state and temperature; gravity changes with position. Density is a property of matter, which has nothing to do with m and V, but changes with state and temperature; inertia is an attribute of an object, which is only related to its mass, It has nothing to do with whether the object is forced or not, whether it is moving or not, and whether it is moving fast or not; specific heat capacity is the property of matter, which is only related to the type and state of matter, and has nothing to do with mass and temperature; resistance is the property of conductor, which is related to the type, length, thickness and temperature of matter, and has nothing to do with current and voltage
4. There are seven elements in scientific inquiry: asking questions, guessing and supposing, making plans and designing experiments, conducting experiments, collecting evidences, analyzing and demonstrating, evaluating, communicating and cooperating
5. Physical methods are embodied in the process of studying physical phenomena to get laws, mainly including analogy method, equivalent substitution method, hypothesis method, control variable method, ideal model method, transformation method, etc, While keeping other factors unchanged (such as exploring the relationship between I and u, R, and what factors are related to evaporation), equivalent substitution method (such as finding resultant force and total resistance), model method (such as nuclear structure model of atom, magnetic induction line and light), analogy method (such as current and water flow, electric pressure and water pressure), conversion method (principle of ammeter, measuring temperature with thermometer and testing magnetic field with small magnetic field)
6. Several points should be noticed in electrical experiment: ① in the process of connecting the circuit, the switch is in the off state. ② before closing the switch, the sliding rheostat is in the maximum resistance state, and the connection method should be one up and one down. ③ the voltmeter should be connected in parallel at both ends of the resistance to be measured, and the ammeter should be connected in series in the circuit. ④ when the ammeter and voltmeter are connected in the circuit, the current must enter from the positive terminal, Flow from negative terminal
7. Can use basic instruments and tools: scale, clock, liquid thermometer, balance (horizontal adjustment, beam balance adjustment, traveling code use), measuring cylinder, measuring cup, spring dynamometer, densimeter, ammeter, voltmeter, sliding rheostat, measuring pen, electric energy meter
8. Transmission medium: Sound: all solid, liquid and gas except vacuum. Light: transparent substances such as vacuum, air, water and glass
9. Common (1) crystal (with a certain melting point): sea wave, ice, quartz, crystal, salt, alum, naphthalene, various metals
(2) Amorphous: rosin, glass, beeswax, asphalt
10. Common (1) conductor: water solution of metal, graphite, human body, earth, acid, alkali and salt
(2) Insulator: rubber, glass, ceramic, plastic, oil
Common heat conductor: metal, bad heat conductor: air, water, wood, cotton, etc
The common new materials are nano materials, superconducting materials, memory alloys and stealth materials
11. The relationship between motion and force
① The original static object: if a is subject to balanced force: keep still. B is subject to unbalanced force: move in the direction of resultant force
② The original moving object: if a is subject to the balanced force: keep the uniform linear motion. B is subject to the unbalanced force: if the direction of the force is the same as that of the motion, the object will accelerate. If the direction of the force is opposite to that of the motion, the object will decelerate. If the direction of the force is not in a straight line with that of the motion, the direction of the object will change
If an object is not forced or balanced, it will remain in equilibrium. If the object is stationary or moving in a straight line at a constant speed, it means that the force is balanced, and the resultant force is 0. If the object is forced by unbalanced force, it will change the state of motion
12. Connection method of home circuit:
① All electrical appliances and sockets are connected in parallel,
② One end of the switch is connected with a live wire, and the other end is connected with a light bulb,
③ The screw sleeve of the screw bulb should be connected to the zero line
④ The fuse is connected to the live wire
⑤ The connection method of three hole socket is left zero and right fire grounding