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Junior high school physics formula mathematics
Junior high school physics formulas, commonly used physics formulas and important knowledge points

Physical quantity unit formula

Name symbol name symbol

Mass m kg kg m=ρv

Temperature t celsius c

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

Density p kg/m3 kg/m3 ρ = m/v.

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

Pressure p pappas card (Pa) P=F/S

Work w joule (coke) W=Fs

Power: watt w P=W/t

Current: I ampere (ampere) A I=U/R

Voltage: u volts (volts) V U=IR.

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

Electric work: Watt Joule (joule) Watt = Watt

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

Heat: joule (joule) j q = centimeter (t-t)

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

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

G: 9.8 N/kg

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

Compilation of junior high school physics formula

Mechanics division

1, speed: V=S/t

2. Gravity: G=mg

3. Density: ρ=m/V

4. pressure: p=F/S

5. Liquid pressure: p=ρgh

6. Buoyancy:

(1), f float = f'-f (pressure difference)

(2), f float = g-f (apparent gravity)

(3), f float = G (float, pause)

(4) Archimedes principle: F float =G row = ρ liquid gV row.

7. Lever balance condition: F 1L 1 = F2L2.

8. ideal slope: f/g = h/l

9. Ideal pulley: F=G/n

10, actual pulley: f = (g+g movement) /n (vertical direction)

1 1, work: W = FS = GH (lifting an object very high)

12, power: p = w/t = Fv.

13, working principle: w hand = W machine.

14, actual machinery: w total = w plus +w extra.

15, mechanical efficiency: η = w /W total.

16, pulley block efficiency:

(1), η = g/nf (vertical direction)

(2), η = g/(g+g motion) (excluding vertical friction)

(3), η = f/nf (horizontal direction)

Branch of thermology

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

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

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)

Common physical quantities

1, speed of light: c = 3×108m/s (in vacuum)

2. Sound speed: V = 340m m/s (15℃)

3. Ear discrimination echo: ≥0. 1s

4. Gravity acceleration: g = 9.8n/kg ≈ 10n/kg.

5. Standard atmospheric pressure: 760mm Hg height =1.01×105pa.

6. Density of water: 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× 103 j/(kg? ℃)

10, elementary charge: e =1.6×10-19c.

1 1. The voltage of one dry cell:1.5v.

12. Voltage of lead battery: 2V.

13. safe voltage of human body: ≤36V (not higher than 36V).

14. voltage of power supply circuit: 380v.

15, household circuit voltage: 220V.

16, unit conversion:

(1), 1 m/s = 3.6 km/h.

(2)、 1g/cm3 = 103kg/m3

(3)、 1kw? h=3.6× 106J

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

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

The resultant force f (N) F =F 1+F2 is in the same direction.

In the opposite direction, F =F 1-F2, f1>; F2 direction is opposite:

Buoyancy f float (N) F float =G object -G line of sight g line of sight: gravity of objects in liquid.

Buoyancy f float (N) F float =G This formula is only applicable.

Buoyancy F float (N) F float =G row =m row g=ρ liquid gV row

Equilibrium conditions of lever F 1L 1= F2L2.

Moving pulley F= G object +G wheel

Pressure p(Pa) P= F/S

Heat Q(J) Q=cm△t

Mechanical work W(J) W=Fs

Power P(w) P=W/t

Mechanical efficiency η= × 100%

Liquid pressure p (pa) p = rhogh

Heat released by fuel combustion Q(J) Q=mq m: mass q: calorific value.

Objects float or suspend.

Row g: gravity of displacement liquid row m: mass of displacement liquid ρ liquid: density of liquid row v: volume of displacement liquid (i.e. volume immersed in liquid).

: power L 1: power arm F2: resistor L2: resistor arm

Crown block F=G object

S=h F: the pulling force of the free end of the rope g: the gravity of the object s: the distance that the free end of the rope moves h: the distance that the object rises.

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.

F: Force S: The distance moved in the direction of force is useful, and W is useful.

Total work w total w has =G substance h

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

W: Working hours.

F: pressure s: stress area

ρ: density of liquid

H: depth (from liquid level to required point)

Vertical distance)

Specific heat m: mass

△ t: change value of temperature

Deformation of Remarks Formula of Physical Quantity (Unit) Formula

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 =F 1-F2 When the direction is opposite, f1> Second generation

Buoyancy f float (N) F float =G object -G line of sight g line of sight: gravity of objects in liquid.

Buoyancy f float (N) F float =G object This formula only applies to floating or suspended objects.

Buoyancy F float (N) F float =G row =m row g=ρ = ρ liquid gV row G row: gravity of displacement liquid m row: mass of displacement liquid ρ liquid: density of liquid V row: volume of displacement liquid (i.e. volume immersed in liquid).

The equilibrium condition of lever F 1L 1 = F2L 1: power L 1: 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 distance that the object rises.

Moving pulley F= (G object +G wheel)

S=2 h G object: object gravity g wheel: moving pulley gravity

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

When the pulley block is placed vertically, the total work w, the total w has =G, and the total h W of the object =Fs.

Mechanical efficiency η= × 100%

Power P(w) P=W/t W: work t: time.

Pressure p(Pa) P= F/S F: pressure s: stress area.

Liquid pressure p (pa) p = rhogh rho: liquid density h: depth (vertical distance from liquid surface to required point)

Heat Q(J) Q=cm△t c: specific heat m: mass △t: temperature change value.

Heat released by fuel combustion Q(J) Q=mq m: mass q: calorific value.

Series circuit: current I (a) I = i 1 = I2 = ... Current is equal everywhere.

Series circuit: voltage u (v) u = u 1+U2+ ... The series circuit acts as a voltage divider.

Series circuit: resistance r (ω) r = r 1+R2+ ...

Parallel circuit: current I (a) I = i 1+I2+ ... The main current is equal to the sum of currents of each branch (shunt).

Parallel circuit: voltage u (v) u = u 1 = U2 = ...

The resistance of parallel circuit r (ω) r =1/r1+1/R2+ ...

Ohm's Law I= U/R The current in the circuit is directly proportional to the voltage and inversely proportional to the resistance.

Current definition formula I=Q/t Q: Charge (Coulomb) T: Time (seconds)

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.

The relationship between electromagnetic wave velocity and wavelength and frequency C=λν C: the speed of light in vacuum.