The basics of physics in junior high school, the meaning of letters, are the basics taught in junior high school. Know and talk about it.

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)

Resultant force: F plus (N) in the same direction : F combined = F1 F2; In the opposite direction: F combined = F1-F2 When the direction is opposite, F1gt; F2

Buoyancy: F float (N) F float = G object - G view (G view: object Gravity of the liquid)

Buoyancy: F float (N) F float = G object (this formula only applies to objects floating or suspended)

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

Balance condition of the lever: F1L1= F2L2 (F1: power; L1: power arm; F2: resistance; L2: resistance arm)

Fixed pulley: F =G object S=h (F: the tension on the free end of the rope; G object: the gravity of the object; S: the distance the free end of the rope moves; h: the distance the object rises)

Moving pulley: F = (G object G wheel)/2 S=2 h (G object: the gravity of the object; G wheel: the gravity of the moving pulley)

Pulley set: F= (G object G wheel) S=n h (n : The number of segments of rope passing through the moving pulley)

Mechanical work: W (J) W=Fs (F: force; s: distance moved in the direction of force)

Useful work: W has = G object h

Total work: W total W total = Fs Applicable when the pulley block is placed vertically

Mechanical efficiency: η=W has/W total × 100

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

Pressure p (Pa) P= F/s (F: pressure; S: force Area)

Liquid pressure: p (Pa) P=ρgh (ρ: density of the liquid; h: vertical distance from the liquid surface to the desired point)

Heat: Q (J) Q=cm△t (c: specific heat capacity of the substance; m: mass; △t: change value of temperature)

Heat released by fuel combustion: Q (J) Q=mq (m : Mass; q: Calorific value)

Commonly used physical formulas and important knowledge points

Series circuit current I (A) I=I1=I2=... The current is equal everywhere

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Series circuit voltage U (V) U=U1 U2... The series circuit acts as a voltage divider

Series circuit resistance R (Ω) R=R1 R2...

Parallel circuit current I (A) I=I1 I2... The main circuit current is equal to the sum of the branch currents (shunt)

Parallel circuit voltage U (V) U=U1=U2=...

Parallel circuit resistance R (Ω) 1/R =1/R1 1/R2…

Ohm’s law: I= U/I

In the circuit Current is directly proportional to voltage and inversely proportional to resistance

Current definition formula I= Q/t (Q: charge (coulomb); t: time (S))

Electrical work :W(J

) W=UIt=Pt (U: voltage; I: current; t: time; P: electrical power)

Electrical power: P=UI=I2R=U2/R (U: voltage; I: current; R: resistance)

The relationship between electromagnetic wave speed, wavelength and frequency: C=λν (C: wave speed (the wave speed of electromagnetic waves is constant, equal to 3×108m/s); λ: wavelength; ν: Frequency)

Several values ??to remember:

a. The propagation speed of sound in air: 340m/s b The propagation speed of light in vacuum or air: 3×108m/s

c. Density of water: 1.0×103kg/m3 d. Specific heat capacity of water: 4.2×103J/(kg?℃)

e. The voltage of a dry cell: 1.5V f. Household circuit voltage: 220V

g. Safety voltage: no higher than 36V