Find the commonly used calculation formula of junior high school science For example, the pressure calculation formula F / s represents the pressure divided by the stress area, which is very common

Find the commonly used calculation formula of junior high school science For example, the pressure calculation formula F / s represents the pressure divided by the stress area, which is very common

All the formulas of junior high school science
Common physical formulas and important knowledge points
1、 Physical formula
Unit) formula remarks formula deformation
Series circuit
Current I (a) I = I1 = I2 = The current is equal everywhere
Series circuit
Voltage U (V) u = U1 + U2 + Start of series circuit
Partial pressure action
Series circuit
Resistance R (Ω) r = R1 + R2 +
Parallel circuit
Current I (a) I = I1 + I2 + The main circuit current is equal to the current of each circuit
Sum of branch currents (shunt)
Parallel circuit
Voltage U (V) u = U1 = U2 =
Parallel circuit
Resistance R (Ω) = +
Ohm's law I=
Current and voltage in circuit
In direct proportion to the resistance
Current definition I=
Q: Charge quantity (Coulomb)
t: Time (s)
Electric work W
(J) W = uit = Pt U: voltage I: current
t: Time p: electric power
Electric power P = UI = I2R = U2 / r u: voltage I: current
R: Resistance
Electromagnetic wave velocity and wave propagation
The relationship between length and frequency C = λ ν C:
Unit formula of physical quantity
Name symbol name symbol
Mass m kg m = PV
Temperature T ° C ° C
Velocity v m / S M / S v = s / T
Density p kg / M 3 kg / m3 P = m / V
Force (gravity) f Newton (cow) n g = mg
Pressure P Pascal PA P = f / S
Work w Joule (joule) J W = FS
Power P watt W P = w / T
Current I a (a) a i = u / R
Voltage U V U = IR
Resistance R ohm (Ω) r = u / I
Electric work w Joule (joule) J W = uit
Electric power P watt (watt) W P = w / T = UI
Heat Q Joule J Q = cm (T-T °)
Specific heat C coke / (kg ° C) J / (kg ° C)
The speed of light in vacuum is 3 × 108 M / s
G 9.8 N / kg
Sound speed 340m / s in air at 15 ° C
Junior high school physics formula compilation
[mechanics part]
1. Speed: v = s / T
2. Gravity: g = mg
3. Density: ρ = m / V
4. Pressure: P = f / S
5. Liquid pressure: P = ρ GH
6. Buoyancy:
(1) F floating = f '- f (pressure difference)
(2) F = G-F (apparent gravity)
(3) , f floating = g (floating, floating)
(4) Archimedes principle: F floating = g row = ρ liquid GV row
7. Lever balance condition: F1 L1 = F2 L2
8. Ideal slope: F / g = H / L
9. Ideal pulley: F = g / n
10. Actual pulley: F = (G + G dynamic) / N (vertical direction)
11. Work: w = FS = GH
12. Power: P = w / T = FV
13. Principle of work: W hand = w machine
14. Actual machine: wtotal = w + W extra
15. Mechanical efficiency: η = w / W
16. Pulley block efficiency:
(1) , η = g / NF (vertical direction)
(2) , η = g / (G + G) (vertical direction without friction)
(3) , η = f / NF (horizontal direction)
[thermal part]
1. Endothermic: q = cm (t-t0) = cm Δ t
2. Exothermic: q = cm (t0-t) = cm Δ t
3. Calorific value: q = q / M
4. Efficiency of furnace and heat engine: η = q efficient utilization / Q fuel
5. Heat balance equation: Q discharge = q suction
6. Thermodynamic temperature: T = t + 273k
[electrical part]
1. Current intensity: I = q electric quantity / T
2. Resistance: r = ρ L / S
3. Ohm's Law: I = u / R
4. Joule's Law:
(1) , q = i2rt universal formula)
(2) , q = uit = Pt = UQ, electric quantity = u2t / R (pure resistance formula)
5. Series circuit:
（1）、I＝I1＝I2
（2）、U＝U1＋U2
（3）、R＝R1＋R2
(4) U1 / U2 = R1 / R2 (partial pressure formula)
（5）、P1/P2＝R1/R2
6. Parallel circuit:
（1）、I＝I1＋I2
（2）、U＝U1＝U2
（3）、1/R＝1/R1＋1/R2 [ R＝R1R2/(R1＋R2)]
(4) I1 / I2 = R2 / R1 (shunt formula)
（5）、P1/P2＝R2/R1
7 constant resistance:
（1）、I1/I2＝U1/U2
（2）、P1/P2＝I12/I22
（3）、P1/P2＝U12/U22
8 electric power:
(1) , w = uit = Pt = UQ (universal formula)
(2) W = i2rt = u2t / R (pure resistance formula)
9 electric power:
(1) , P = w / T = UI (universal formula)
(2) , P = I2R = U2 / R (pure resistance formula)
Common physical quantities
1. Speed of light: C = 3 × 108m / S (in vacuum)
2. Sound speed: v = 340m / S (15 ℃)
3. Echo discrimination of human ear: ≥ 0.1s
4. Acceleration of gravity: g = 9.8n/kg ≈ 10N / kg
5. Standard atmospheric pressure value:
760 mm mercury column height = 1.01 × 105 pa
6. Water density: ρ = 1.0 × 103kg / m3
7. Freezing point of water: 0 ℃
8. Boiling point of water: 100 ℃
9. Specific heat capacity of water:
C＝4．2×103J/(kg?℃)
10. Elementary charge: e = 1.6 × 10-19c
11. Voltage of one dry cell: 1.5V
12. Voltage of one lead-acid battery: 2V
13. Safety voltage for human body: ≤ 36V (not higher than 36V)
14. Power circuit voltage: 380V
15. Home circuit voltage: 220 V
16. Unit conversion:
（1）、1m/s＝3．6km/h
（2）、1g/cm3 ＝103kg/m3
（3）、1kw?h＝3．6×106J
Chemical reaction
1. Combustion of magnesium in air: 2mg + O2 ignites 2MgO
2. Combustion of iron in oxygen: 3Fe + 2O2 ignites Fe3O4
3. Combustion of aluminum in air: 4Al + 3O2 ignites 2al2o3
4. Combustion of hydrogen in air: 2h2 + O2 ignites 2H2O
5. Combustion of red phosphorus in air: 4P + 5o2 ignites 2p2o5
6. Sulfur powder burning in air: S + O2 ignites SO2
7. Full combustion of carbon in oxygen: C + O2 ignites CO2
8. Incomplete combustion of carbon in oxygen: 2C + O2 ignites 2CO
9. Carbon dioxide passing through hot carbon layer: C + CO2 high temperature 2CO
10. Combustion of carbon monoxide in oxygen: 2CO + O2 ignites 2co2
11. Reaction of carbon dioxide and water (carbon dioxide into purple litmus test solution): CO2 + H2O = = = H2CO3
12. Quicklime dissolved in water: Cao + H2O = = = Ca (OH) 2
13. Anhydrous copper sulfate as desiccant: CuSO4 + 5H2O = = = = CuSO4? 5H2O
14. Combustion of sodium in chlorine: 2Na + Cl2 ignites 2nacl
decomposition reaction
15. Preparation of oxygen from hydrogen peroxide in laboratory: 2h2o2, MnO2, 2H2O + O2 ↑
16. Heating potassium permanganate: 2kmno4 heating k2mno4 + MnO2 + O2 ↑
17. Under the action of direct current, water is electrified by 2H2O, 2h2 ↑ + O2 ↑
18. The carbonic acid is unstable and separated into H2CO3 = = = H2O + CO2 ↑
19. High temperature calcined limestone (carbon dioxide industrial process): CaCO3 high temperature CaO + CO2 ↑
Displacement reaction
20. Reaction of iron with copper sulfate solution: Fe + CuSO4 = = FeSO4 + Cu
21. Reaction of zinc with dilute sulfuric acid (hydrogen production in laboratory): Zn + H2SO4 = = ZnSO4 + H2 ↑
22. Reaction of magnesium with dilute hydrochloric acid: Mg + 2HCl = = = MgCl2 + H2 ↑
23. Reduction of copper oxide by hydrogen: H2 + CuO heating Cu + H2O
24. Reduction of CuO by charcoal: C + 2CuO, high temperature 2Cu + CO2 ↑
25. Methane burning in air: CH4 + 2O2 ignites CO2 + 2H2O
26. Water vapor passes through the hot carbon layer: H2O + C, high temperature H2 + Co
27. Coke reduced iron oxide: 3C + 2fe2o3, high temperature 4Fe + 3co2 ↑
other
28. Reaction of sodium hydroxide solution with copper sulfate solution: 2naoh + CuSO4 = = Cu (OH) 2 ↓ + Na2SO4
29. Methane burning in air: CH4 + 2O2 ignites CO2 + 2H2O
30. Alcohol burning in air: C2H5OH + 3O2 ignites 2co2 + 3H2O
31. Reduction of copper oxide by carbon monoxide: CO + CuO heating Cu + CO2
32. Carbon monoxide reduced iron oxide: 3Co + Fe2O3, high temperature 2Fe + 3co2
33. Carbon dioxide: Ca (OH) 2 + CO2 = = = = CaCO3 ↓ + H2O
34. Reaction of sodium hydroxide with carbon dioxide (removal of carbon dioxide): 2naoh + CO2 = = = = Na2CO3 + H2O
35. Reaction of limestone (or marble) with dilute hydrochloric acid (laboratory preparation of carbon dioxide): CaCO3 + 2HCl = = = CaCl2 + H2O + CO2 ↑
36, sodium carbonate and concentrated hydrochloric acid reaction (foam extinguisher principle): Na2CO3 + 2HCl = = = 2NaCl + H2O + CO2
1、 Reaction of substance with oxygen:
(1) The reaction of elemental matter with oxygen is as follows
1. Combustion of magnesium in air: 2mg + O2 ignites 2MgO
2. Combustion of iron in oxygen: 3Fe + 2O2 ignites Fe3O4
3. Copper heated in air: 2Cu + O2 heated 2CuO
4. Combustion of aluminum in air: 4Al + 3O2 ignites 2al2o3
5. Combustion in hydrogen and air: 2h2 + O2 ignites 2H2O
6. Combustion of red phosphorus in air: 4P + 5o2 ignites 2p2o5
7. Sulfur powder burning in air: S + O2 ignites SO2
8. Full combustion of carbon in oxygen: C + O2 ignites CO2
9. Incomplete combustion of carbon in oxygen: 2C + O2 ignites 2CO
(2) Reaction of compound with oxygen:
10. Combustion of carbon monoxide in oxygen: 2CO + O2 ignites 2co2
11. Methane combustion in air: CH4 + 2O2 ignites CO2 + 2H2O
12. Alcohol burning in air: C2H5OH + 3O2 ignites 2co2 + 3H2O
2、 There are several decomposition reactions
13. Under the action of direct current, water is electrified by 2H2O, 2h2 ↑ + O2 ↑
14. Heating basic copper carbonate: Cu2 (OH) 2CO3 heating 2CuO + H2O + CO2 ↑
15. Heating potassium chlorate (with a small amount of manganese dioxide): 2kclo3 = = = = 2KCL + 3O2 ↑
16. Heating potassium permanganate: 2kmno4 heating k2mno4 + MnO2 + O2 ↑
17. Carbonic acid is not stable, but H2CO3 = = = H2O + CO2 ↑
18. High temperature calcined limestone: CaCO3, high temperature CaO + CO2 ↑
3、 There are several redox reactions
19. Reduction of CuO by hydrogen: H2 + CuO heating Cu + H2O
20. Reduction of CuO by charcoal: C + 2CuO, high temperature 2Cu + CO2 ↑
21. Reduction of iron oxide by coke: 3C + 2fe2o3, high temperature 4Fe + 3co2 ↑
22. Reduction of Fe3O4 by coke: 2C + Fe3O4, high temperature 3Fe + 2co2 ↑
23. Reduction of copper oxide by carbon monoxide: CO + CuO heating Cu + CO2
24. Reduction of iron oxide by carbon monoxide: 3Co + Fe2O3, high temperature 2Fe + 3co2
25. Reduction of Fe3O4 by carbon monoxide: 4Co + Fe3O4, high temperature 3Fe + 4co2
4、 The relationship among element, oxide, acid, alkali and salt
(1) Metal element + acid -------- Salt + hydrogen (displacement reaction)
26. Zinc and dilute sulfuric acid Zn + H2SO4 = ZnSO4 + H2 ↑
27. Iron and dilute sulfuric acid Fe + H2SO4 = FeSO4 + H2 ↑
28. Magnesium and dilute sulfuric acid Mg + H2SO4 = MgSO4 + H2 ↑
29. Aluminum and dilute sulfuric acid 2Al + 3h2so4 = Al2 (SO4) 3 + 3h2 ↑
30. Zinc and dilute hydrochloric acid Zn + 2HCl = = = ZnCl2 + H2 ↑
31. Iron and dilute hydrochloric acid Fe + 2HCl = = = FeCl2 + H2 ↑
32. Magnesium and dilute hydrochloric acid Mg + 2HCl = = = MgCl2 + H2 ↑
33. Aluminum and dilute hydrochloric acid 2Al + 6hcl = = 2alcl3 + 3h2 ↑
(2) Metal element + salt (solution) -- another metal + another salt
34. Reaction between iron and copper sulfate solution: Fe + CuSO4 = = = FeSO4 + Cu
35. Reaction between zinc and copper sulfate solution: Zn + CuSO4 = = = ZnSO4 + Cu
36. Reaction of copper with mercuric nitrate solution: Cu + Hg (NO3) 2 = = = Cu (NO3) 2 + Hg
(3) Alkaline oxide + acid -------- Salt + water
37. Reaction of iron oxide with dilute hydrochloric acid: Fe2O3 + 6hcl = = = 2fecl3 + 3H2O
38. Reaction of iron oxide with dilute sulfuric acid: Fe2O3 + 3h2so4 = = = Fe2 (SO4) 3 + 3H2O
39. Reaction of copper oxide with dilute hydrochloric acid: CuO + 2HCl = = = = CuCl2 + H2O
40. Reaction of copper oxide with dilute sulfuric acid: CuO + H2SO4 = = = = CuSO4 + H2O
41. Reaction of magnesium oxide with dilute sulfuric acid: MgO + H2SO4 = = = = MgSO4 + H2O
42. Reaction of calcium oxide with dilute hydrochloric acid: Cao + 2HCl = = = = CaCl2 + H2O
(4) Acid oxide + alkali salt + water
43. Deterioration of caustic soda exposed to air: 2naoh + CO2 = = = = Na2CO3 + H2O
44. Caustic soda absorbs sulfur dioxide: 2naoh + SO2 = = = = Na2SO3 + H2O
45. Caustic soda absorbs sulfur trioxide gas: 2naoh + SO3 = = = = Na2SO4 + H2O
46. Slaked lime metamorphoses in air: Ca (OH) 2 + CO2 = = = = CaCO3 ↓ + H2O
47. Absorption of sulfur dioxide by hydrated lime: Ca (OH) 2 + SO2 = = = = CaSO3 ↓ + H2O
(5) Acid + alkali salt + water
48. Hydrochloric acid reacts with caustic soda: HCl + NaOH = = = = NaCl + H2O
49. Reaction of hydrochloric acid and potassium hydroxide: HCl+