Mechanics  Keys 

d = 0.5 g t^{2} F_{g} = (G m_{1} m_{2} )/r^{2} g = (4 p² L)/t^{2} P = F/A r = m/V v = d/t W = F·d (dot product) T = F × d (cross product) 
A = Area a = coeficient of linear friction c = specific heat capacity D = change in d = distance F = Force F_{e}= Electrical force F_{g} = Force of gravitational attraction f = frequency g = acceleration of gravity G = 6.67 x 10^{11} i = current L = Length L_{i} = initial length L_{f} = final length DL = change in length ( L_{f}  L_{i} ) l = waveLength m = mass P = power P = Pressure r = density p = 3.1415926535897932384626433832795... q = charge Q = Energy or Work ( usually in calories) r = radius R = Resistance t = time T_{f} = final Temperature T_{i} = initial Temperature DT = change in Temperature (T_{f}  T_{i}) T = Torque t = period v = velocity V = Voltage V = Volume W = Energy or Work (usually Joules) 
Heat  
Q = m c DT DL = a L_{i} DT DT = T_{f}  T_{i} 

Waves and Sound  
v = f l f = 1/t 

Electricity  
F_{e} = [(9×10^{9}) q_{1} q_{2} ]/r^{2} i = q/t P = i V V = i R P = i^{2} R 