 # 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 Year 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                volume 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                                strength 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        A 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 = IDt 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          A 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          r 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                 r2 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         V 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