Force and motion力和运动 

velocity, v=Δs/Δt 

acceleration, a=Δv/Δt 

v=u+at 

s=ut+1/2 at² 

v²=u²+2as 

s=(u+v)t/2  

resultant force, F=ma 

weight, W=mg 

torque of a couple=force×perpendicular distance between forces 

work done, W=Fscosθ (θ is the angle between F and s) 

gravitational potential energy, GPE=mgh 

kinetic energy, KE=1/2 mv² 

internal energy, U=∑PE+∑KE

power, P=W/t=Fv 

momentum, p=mv 

resultant force, F=∆p/∆t 

conservation of momentum,

m₁ u₁+m₂ u₂=m₁ v₁+m₂ v₂ 

density, ρ=m/V 

pressure, p=F/A 

pressure, p=ρgh 

Materials 材料学

tension, F=kx 

stress, σ=(force))/(cross-sectional area) 

strain, ε=(extention))/(original length)) 

Young modulus, E=σ/ε 

elastic potential energy or strain energy,

E=1/2 Fx=1/2 kx² 

Electricity 电学

electric field strength, E=F/Q 

electric field strength in a uniform field, E=-V/d 

current, 

I=∆Q/∆t 

I=nAvq 

the elementary charge, e=-1.6×10^-19 C 

potential difference, V=∆W/∆Q 

resistance, R=V/I 

power, P=VI=V²/R=I² R 

work done, ∆W=VI∆t 

combined resistance of resistors in series,

combined resistance of resistors in parallel,

resistivity, ρ=RA/l 

terminal p.d.,V=e.m.f.-Ir 

potential divider circuit,

electron volt,1eV=1.6×10^-19J 

Waves 波 

frequency,f=1/T 

wave speed,v=fλ 

intensity,I∝A²

constructive interference,path difference=nλ=(2n)λ/2

destructive interference, path difference=(2n+1)  λ/2 

double-slit diffraction, λ=ax/D 

diffraction grating, dsinθ=nλ 

When the observer is at rest, observed frequency,