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.