Edexcel GCSE Physics Equations: What You Must Memorise vs What's on the Formula Sheet

In Edexcel GCSE Physics (1PH0), you are given a formula sheet in the exam. This is good news, but it creates a trap: students assume they do not need to learn any equations. That assumption costs marks every year.

The formula sheet only contains some of the equations. The rest must be recalled from memory. If you cannot remember an equation that is not on the sheet, you cannot answer the question.

This guide splits every equation into two clear sections -- those you must memorise and those provided on the formula sheet -- with worked examples for each. A third section covers essential exam technique for equation questions.

Section 1: Equations You Must Memorise

These equations are NOT on the formula sheet. You must learn them by heart. If you walk into the exam without these committed to memory, you will lose marks.

Weight

W = mg

• W = weight (N)
• m = mass (kg)
• g = gravitational field strength (N/kg), 9.8 N/kg on Earth

Example: A bag has a mass of 1.5 kg. W = 1.5 x 9.8 = 14.7 N

Work Done

W = Fs

• W = work done (J)
• F = force (N)
• s = distance moved in the direction of the force (m)

Example: A force of 40 N pushes a trolley 12 m. W = 40 x 12 = 480 J

Kinetic Energy

KE = 1/2 mv^2

• KE = kinetic energy (J)
• m = mass (kg)
• v = speed (m/s)

Example: A 1200 kg car at 15 m/s. KE = 1/2 x 1200 x 15^2 = 135,000 J (135 kJ)

Velocity is squared, so doubling the speed quadruples the kinetic energy. This is one of the most commonly tested relationships in the exam.

Gravitational Potential Energy

GPE = mgh

• GPE = gravitational potential energy (J)
• m = mass (kg)
• g = gravitational field strength (N/kg)
• h = height (m)

Example: A 70 kg climber ascends 25 m (g = 9.8). GPE = 70 x 9.8 x 25 = 17,150 J

Power

P = E/t and P = W/t

• P = power (W)
• E = energy transferred (J)
• W = work done (J)
• t = time (s)

Both versions say the same thing: power is the rate of energy transfer or the rate of doing work.

Example: A motor transfers 6000 J in 30 s. P = 6000 / 30 = 200 W

Efficiency

Efficiency = useful output energy transfer / total input energy transfer

Also written as: Efficiency = useful output power / total input power

No unit. Expressed as a decimal (0 to 1) or as a percentage (multiply by 100).

Example: A lamp receives 60 J and converts 9 J to light. Efficiency = 9 / 60 = 0.15 (15%)

Wave Speed

v = f lambda

• v = wave speed (m/s)
• f = frequency (Hz)
• lambda = wavelength (m)

Example: Frequency 256 Hz, wavelength 1.3 m. v = 256 x 1.3 = 332.8 m/s

Speed

v = s/t

• v = speed (m/s)
• s = distance (m)
• t = time (s)

Example: A cyclist covers 450 m in 90 s. v = 450 / 90 = 5 m/s

Acceleration

a = (delta v) / t

• a = acceleration (m/s^2)
• delta v = change in velocity (m/s)
• t = time taken (s)

Example: A car goes from 5 m/s to 20 m/s in 6 s. a = (20 - 5) / 6 = 2.5 m/s^2

Density

rho = m/V

• rho = density (kg/m^3)
• m = mass (kg)
• V = volume (m^3)

Example: Mass 2.4 kg, volume 0.003 m^3. rho = 2.4 / 0.003 = 800 kg/m^3

Pressure

P = F/A

• P = pressure (Pa)
• F = force (N)
• A = area (m^2)

Example: 600 N on 0.04 m^2. P = 600 / 0.04 = 15,000 Pa

Charge

Q = It

• Q = charge (C)
• I = current (A)
• t = time (s)

Example: 0.5 A for 120 s. Q = 0.5 x 120 = 60 C

Voltage (Potential Difference)

V = IR

• V = potential difference (V)
• I = current (A)
• R = resistance (ohms)

Example: 3 A through 8 ohms. V = 3 x 8 = 24 V

Electrical Power

P = IV and P = I^2 R

• P = power (W)
• I = current (A)
• V = potential difference (V)
• R = resistance (ohms)

Example: A heater draws 4 A at 230 V. P = 4 x 230 = 920 W

Energy Transferred (Electrical)

E = Pt and E = QV

• E = energy (J)
• P = power (W)
• t = time (s)
• Q = charge (C)
• V = potential difference (V)

Example: A 2000 W kettle runs for 180 s. E = 2000 x 180 = 360,000 J (360 kJ)

Period and Frequency

T = 1/f

• T = period (s)
• f = frequency (Hz)

Example: A wave has a frequency of 50 Hz. T = 1/50 = 0.02 s

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Section 2: Equations on the Formula Sheet

These equations are provided in the exam. You do not need to memorise them, but you must know what they mean, when to use them, and how to substitute values correctly.

Newton's Second Law

F = ma

• F = resultant force (N), m = mass (kg), a = acceleration (m/s^2)

Used in any question linking force, mass and acceleration. Common in Topic 2, often combined with free-body diagrams where you must calculate the resultant force before substituting.

Example: Resultant force 4500 N on a 1500 kg car. a = F/m = 4500 / 1500 = 3 m/s^2

Momentum

p = mv

• p = momentum (kg m/s), m = mass (kg), v = velocity (m/s)

Used in conservation of momentum questions involving collisions or explosions. Total momentum before an event equals total momentum after, provided no external forces act.

Example: A 0.4 kg ball at 5 m/s. p = 0.4 x 5 = 2 kg m/s

Force and Change in Momentum (Higher)

F = (delta p) / t

• F = force (N), delta p = change in momentum (kg m/s), t = time (s)

Used in car safety questions. Crumple zones, airbags and seatbelts all increase the time of impact, which reduces the force on the occupant for the same change in momentum.

Example: A 60 kg person decelerates from 15 m/s to 0 in 0.5 s. delta p = 900 kg m/s. F = 900 / 0.5 = 1800 N

Equations of Motion (Higher)

v^2 = u^2 + 2as

• v = final velocity (m/s), u = initial velocity (m/s), a = acceleration (m/s^2), s = distance (m)

Used when time is not given. Common in braking distance calculations where the car decelerates from speed u to rest (v = 0).

Example: Car at 20 m/s brakes at -5 m/s^2. 0 = 400 + 2(-5)s. s = 40 m

Force and Extension (Hooke's Law)

F = kx

• F = force (N), k = spring constant (N/m), x = extension (m)

Used in Hooke's Law questions. Only valid up to the limit of proportionality. Beyond that point, the spring deforms permanently and the equation no longer applies.

Example: Spring with k = 50 N/m stretched 0.2 m. F = 50 x 0.2 = 10 N

Elastic Potential Energy

E = 1/2 kx^2

• E = elastic potential energy (J), k = spring constant (N/m), x = extension (m)

Used for calculating energy stored in a stretched or compressed spring. Often paired with energy transfer questions where elastic PE converts to kinetic energy.

Example: Spring (k = 80 N/m) stretched 0.15 m. E = 1/2 x 80 x 0.0225 = 0.9 J

Specific Heat Capacity

delta E = mc delta theta

• delta E = change in thermal energy (J), m = mass (kg), c = specific heat capacity (J/kg degrees C), delta theta = temperature change (degrees C)

Used in heating and cooling calculations. Core practical context: measuring specific heat capacity of a metal block using an immersion heater, joulemeter and thermometer.

Example: 2 kg water (c = 4200) heated from 20 to 80 degrees C. delta E = 2 x 4200 x 60 = 504,000 J

Specific Latent Heat

E = mL

• E = energy (J), m = mass (kg), L = specific latent heat (J/kg)

Used for changes of state -- melting, boiling, freezing or condensing -- where temperature stays constant but energy is still being transferred to break or form intermolecular bonds.

Example: Boil 0.5 kg water (L = 2,260,000 J/kg). E = 0.5 x 2,260,000 = 1,130,000 J

Pressure in Fluids

P = rho g h

• P = pressure (Pa), rho = fluid density (kg/m^3), g = gravitational field strength (N/kg), h = depth (m)

Used for calculating pressure at a given depth in a liquid. Often tested alongside P = F/A to find the force on a surface at depth.

Example: Pressure at 5 m depth in water (rho = 1000, g = 9.8). P = 1000 x 9.8 x 5 = 49,000 Pa

Transformer Equation

Vp/Vs = Np/Ns

• Vp, Vs = primary and secondary voltages (V), Np, Ns = number of turns on primary and secondary coils

Used for calculating the output voltage of a transformer or determining the turns ratio needed to achieve a target voltage.

Example: 200 primary turns, 1000 secondary turns, input 12 V. Vs = 12 x 1000/200 = 60 V

Transformer Power (Higher)

Vp Ip = Vs Is

• Vp, Vs = primary and secondary voltages (V), Ip, Is = primary and secondary currents (A)

Assumes 100% efficiency. If a transformer steps voltage up, current goes down proportionally, and vice versa.

Example: 230 V to 11.5 V, primary current 0.5 A. Is = (230 x 0.5) / 11.5 = 10 A

Motor Effect (Higher)

F = BIl

• F = force on conductor (N), B = magnetic flux density (T), I = current (A), l = length of conductor in field (m)

Used for calculating the force on a current-carrying wire in a magnetic field. The direction of the force is given by Fleming's left-hand rule.

Example: Wire 0.3 m, 4 A, field 0.05 T. F = 0.05 x 4 x 0.3 = 0.06 N

Parallel Resistance (Higher)

1/R = 1/R1 + 1/R2

• R = total resistance (ohms), R1 and R2 = individual resistances (ohms)

The total resistance of parallel resistors is always less than the smallest individual resistance. A common error is to forget to take the reciprocal at the end of the calculation.

Example: 6 ohm and 12 ohm in parallel. 1/R = 1/6 + 1/12 = 3/12. R = 4 ohms

Explore LearningBro's Edexcel GCSE Physics courses for exam-style practice.

Section 3: Tips for Using Equations in the Exam

How to Rearrange Equations

The formula triangle method works reliably for equations with three variables. Place the quantity that is alone on one side of the equation at the top of the triangle and the two multiplied quantities at the bottom. Cover what you want to find: if the remaining two are side by side, multiply; if one is above the other, divide.

For V = IR: place V on top, I and R on the bottom. To find R, cover R to get V/I. To find I, cover I to get V/R.

For equations like KE = 1/2 mv^2, the triangle method does not apply neatly. You need algebraic rearrangement: v^2 = 2KE/m, then v = square root of (2KE/m). Practise these rearrangements until they are automatic.

Showing Working for Method Marks

Edexcel awards method marks for showing your process, not just the final answer. Always follow this structure:

1. Write the equation you are using.
2. Substitute the values.
3. Calculate the answer.
4. State the answer with the correct unit.

If you make an arithmetic error but your method is correct, you can still earn 2 out of 3 marks on a typical calculation. If you only write a final number with no working, you risk scoring zero even if the number is correct.

Unit Conversions You Must Know

The exam frequently gives values in non-standard units. Always convert before substituting into the equation.

• km/h to m/s: divide by 3.6 (e.g., 72 km/h = 20 m/s)
• kW to W: multiply by 1000 (e.g., 2.5 kW = 2500 W)
• kWh to J: multiply by 3,600,000 (1 kWh = 3.6 MJ)
• Minutes to seconds: multiply by 60
• Hours to seconds: multiply by 3600
• cm to m: divide by 100
• g to kg: divide by 1000
• cm^3 to m^3: divide by 1,000,000

A useful check: if your answer is absurdly large or small, you have probably forgotten a unit conversion.

Common Mistakes

These errors appear repeatedly in examiner reports. Being aware of them will save you marks.

Forgetting to square velocity in KE. Students write KE = 1/2 x m x v instead of KE = 1/2 x m x v^2. This is one of the most frequent errors in the entire exam.

Mixing up mass and weight. Mass is in kg and does not change with location. Weight is a force in N and depends on gravitational field strength. If a question gives mass but the equation needs weight, use W = mg first.

Using the wrong power equation. P = IV is for electrical circuits. P = E/t is the general definition of power. Read the context carefully before choosing.

Not converting units. If the question gives distance in km and time in hours but asks for speed in m/s, you must convert before calculating.

Rounding too early. Keep intermediate values to at least 3 significant figures. Only round your final answer. Early rounding can push your answer outside the acceptable range on the mark scheme.

Ignoring direction. In momentum and acceleration questions, direction matters. If two objects move in opposite directions, one velocity must be treated as negative. Forgetting this leads to incorrect answers in collision problems.

Pulling It All Together

The most effective way to prepare for equation questions is to practise with past papers under timed conditions. At the start of each session, write out all 16 recall equations from memory. Keep doing this until you can produce them all without hesitation. For the formula sheet equations, focus on recognising which equation fits each question and substituting values correctly.

For a broader overview of the specification, see our Edexcel GCSE Physics Revision Guide. To understand what examiners are looking for in written answers, read Edexcel GCSE Exam Command Words Explained and How Edexcel Mark Schemes Work.

Explore all Edexcel GCSE Physics courses on LearningBro and start practising with exam-style questions today.