Physics Equations

These are all of the equations you used to need to recall for Physics examinations... at each stage it was assumed you remembered the ones from the previous stage... so it was worth transferring them properly to your mental 'hard drive'!

The English examination boards now GIVE you equations - so you no longer get marks for recalling them. However, I would argue that actually knowing them makes it easier for you to explain a physics principle.

For example if you KNOW that F=ma, then, in answer to, 'What comprises evedence of a force acting?', you know that a net force will make a body accelerate.

Having a mathematical mind myself I find learning equations to be a shorthand way of learning Physics!

Make sure you know the correct units.......... all units to be used in equations should be in their basic form (no prefixes) - EXCEPT mass - that is kg!

Remember to take care when you write the equation letters... they are symbols NOT part of your handwriting!
Special care with I for current it shouldn't be possible to confuse it with l for length or 1 (the number one)!


Equation in words
Symbolic representation
Key Stage
speed = distance travelled

                time taken

v = d/t Y7 KS3

acceleration = change in velocity

                       time taken

 a = Dv/t  Y8 KS3
 density = mass
r = m/V  Y7 KS3
force = mass x acceleration F = ma  Y9 KS3
work done = force x distance moved in the direction of that force W = Fs  Y9 KS3
momentum = mass x velocity p = mv  Y12 AS
 power = energy transferred 
time taken
 P = E/t  Y8  KS3
 power = work done
time taken
  P = W/t  Y9  KS3
 weight = mass x gravitational field
w = mg  Y7  KS3
kinetic energy = half x mass x (velocity squared) EK= 1/2mv2  Y12  KS4
change in gravitational potential energy = mass x gravitational field strenth x  difference in height  DGPE = mgDh  Y9  KS3
 pressure = force applied
                  contact area
 P = F
 Y7  KS3
Gas Law: pressure x volume of a gas = number of moles x molar gas constant x absolute temperature  pV = nRT  Y12  AS
Gas Law: combination of Boyle's Law and Charles' Law  P1V1 = P2V2
   T1      T2
NB Temperature MUST be in Kelvin
Y11 KS4
charge = current x time  DQ = ID  Y10  KS4
 Ohm's Law: Potential difference = current x resistance  V = IR  Y8  KS3
 Ohm's Law applied to the full circuit: Electromotive force = current x (sum of the circuit resistance and the internal resistance of the cell)   EMF = I(R + r)  Y12  AS
 power = current x potential difference  P = I V  Y8  KS3
energy transferred in a component = charge passing through it x potential difference acorss it  W = QV  Y10  KS4
resistance = resistivity x length
                  cross sectional area
 R = r l
 Y12  AS
 wavespeed = frequency x wavelength  v = fl
for electromagnetic radiation v = c giving:
c = fl
 Y8  KS3
centripetal force = mass x speed2
                            radius of path
 FC = mv2
 Y13  A2
Electrical energy changed into heat = potential difference x current x time  E = VI t  Y9  KS3
Inverse square law for force on a mass in a gravitational field of another mass: Force is proportional to the product of the masses and inversely proportional to the square of the distance between them FG = - G m1 m2

NB the minus sign indicates it is ALWAYS attractive

Y13 A2
Inverse square law for force on a charge in an electric field of another charge: Force is proportional to the product of the charges and inversely proportional to the square of the distance between them FE=   1   Q1 Q2
       4pe0    r2

NB the overall sign indicating wherther it is attractive (negative) or repulsive (positive) comes from the signs of the charges.
Also, although the constant of proportionality is complex it is a similar relationship to above.

Y13 A2
capacitance =    charge stored 
                      potential difference
C =  Q
Y13 A2
ratio of the voltages across the coils of a transformer = the ratio of the turns on the coils V1   =    N1
V2         N2
NB the 1 could be P for primary and the 2 could be s for secondary - it doesn't matter which is which!
Y11 KS4


LOJ November 2000/revised October 2001/revised November 2002 and November 2010