Which formulae are not in the IB Physics data booklet?

Several important formulae are not included in the IB Physics data booklet and must be memorised. These include: average velocity (v = Δs/Δt), projectile components (vx = v cosθ, vy = v sinθ), Newton's three laws, conservation of momentum, the impulse equation, centripetal force (F = mv²/r), the work-energy theorem, the defining equation of SHM (a = -ω²x), the de Broglie equation (λ = h/p), and the notation for alpha and beta decay. HL students also need angular velocity, moment of inertia for a disk, and the AC generator EMF equation.

Do you get a formula sheet in IB Physics?

Yes. IB Physics students are given the IB Physics data booklet in all three papers. It contains most of the formulae, constants, and values you need. However, it does not contain every formula. Some equations, including Newton's laws, conservation of momentum, the work-energy theorem, and several others must be memorised. Knowing which ones are missing is an important part of exam preparation.

Do you need to memorise Newton's laws for IB Physics?

Yes. Newton's three laws of motion are not listed in the IB Physics data booklet. You need to know them as statements and as equations: ΣF = 0 for Newton's first law, F = ma for Newton's second law, and F_AB = -F_BA for Newton's third law. They appear frequently in Paper 1A and Paper 2 across multiple topics.

What is the de Broglie equation in IB Physics?

The de Broglie equation states that all particles have wave-like properties. The de Broglie wavelength λ is given by λ = h/p, where h is Planck's constant and p is the momentum of the particle (p = mv). This equation is not in the data booklet and must be memorised. It is assessed in the E.2 Quantum Physics topic and often appears in Paper 2 extended response questions.

How do I write alpha and beta decay equations in IB Physics?

In alpha decay, the parent nucleus loses 2 protons and 2 neutrons, emitting a helium-4 nucleus. The mass number decreases by 4 and the atomic number decreases by 2. In beta-minus decay, a neutron becomes a proton, the mass number stays the same and the atomic number increases by 1. An electron and an antineutrino are emitted. You must include the antineutrino in beta decay equations to gain full marks. These decay notations are not in the data booklet.

IB Physics Formulae You Need to Memorise (Not in the Data Booklet)

Here is something that surprises a lot of IB Physics students:

The data booklet does not contain every formula you need.

Most equations are in there. But some are not. And if you walk into the exam assuming the data booklet has you covered, you will hit questions where you are expected to recall something from memory and you won’t have it.

This post lists every formula that is missing from the data booklet, organised by topic, with a brief explanation of what each one means. Work through it alongside your revision and make sure every single one is locked in before exam day.

Your goal is not to know everything. Your goal is to lose as few marks as possible.

For the complete revision system that puts all of this in context, read the how to study IB Physics guide.

Theme A: Space, Time and Motion

A.1 Kinematics

Average velocity

This one is surprisingly easy to forget because it feels too basic. But it comes up in Paper 2 and in Paper 1A data questions. Average velocity is displacement divided by time:

v̄ = Δs / Δt

Horizontal and vertical components of a projectile

These resolve a velocity into its components using the launch angle θ:

vₓ = v cos θ

vᵧ = v sin θ

The horizontal component stays constant throughout the motion (no horizontal force). The vertical component changes due to gravity. If you can draw this as a right-angled triangle and label it correctly, you will handle almost any projectile question the exam throws at you.

A.2 Forces and Momentum

Terminal velocity

At terminal velocity, the net force is zero. The drag force equals the weight:

F_drag = mg (or equivalently: ΣF = 0)

Newton’s Laws

These are not in the data booklet because the IB expects you to know them as fundamental statements, not just equations.

Newton’s 1st Law: if the net force is zero, a body remains at rest or moves in a straight line at constant velocity:

ΣF = 0

Newton’s 2nd Law: net force equals the rate of change of momentum. For constant mass:

F = ma

Newton’s 3rd Law: action and reaction forces are equal in magnitude, opposite in direction, and act on different bodies:

F_AB = -F_BA

Conservation of Momentum

For a closed system (no external forces), total momentum before equals total momentum after:

m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂

This applies to both collisions and explosions. In an explosion, both objects start at rest, so the left-hand side is zero.

Impulse

Impulse equals the change in momentum. You need both forms:

J = FΔt

J = Δp = mv − mu

Centripetal Force

The net force directed towards the centre of a circular path:

F = mv² / r

A.3 Work, Energy and Power

Mechanical energy conservation

When no non-conservative forces act (no friction, no air resistance), total mechanical energy is constant:

½mv² + mgh = constant

Or equivalently: KE₁ + PE₁ = KE₂ + PE₂

Work-Energy Theorem

The net work done on an object equals its change in kinetic energy:

W_net = ΔKE = ½mv² − ½mu²

A.4 Rigid Body Mechanics (HL only)

Average angular velocity

Analogous to linear average velocity, but for rotation:

ω̄ = Δθ / Δt

Moment of inertia for a solid cylinder or disk (about the central axis):

I = ½mr²

Conservation of angular momentum

If no external torque acts, angular momentum is conserved:

L = Iω = constant

Rotational equilibrium

For an extended body to be in rotational equilibrium, the sum of all torques about any axis must be zero:

Στ = 0

Total mechanical energy (when both translational and rotational motion are present):

E = ½mv² + ½Iω²

Theme B: The Particulate Nature of Matter

B.1 Thermal Energy Transfers

Average speed of gas molecules

This connects temperature to molecular motion:

v_rms = √(3kT / m)

where k is the Boltzmann constant, T is temperature in kelvin, and m is the mass of one molecule.

B.3 Gas Laws

The link between Boltzmann constant, gas constant, and Avogadro’s number:

k_B = R / N_A

This is worth memorising because it lets you move between the molecular and molar forms of the gas equations.

The individual gas laws (useful for multi-step problems):

Boyle’s Law (constant temperature): pV = constant

Charles’s Law (constant pressure): V / T = constant

Gay-Lussac’s Law (constant volume): p / T = constant

Combined: p₁V₁ / T₁ = p₂V₂ / T₂

B.5 Current and Circuits

Internal resistance

The full form of the EMF equation, showing the terminal voltage drop:

ε = I(R + r) or equivalently V = ε − Ir

where ε is the EMF, r is the internal resistance, R is the external resistance, and V is the terminal voltage.

Theme C: Wave Behaviour

C.1 Simple Harmonic Motion

The defining equation of SHM

This is the one that defines what SHM actually is. Acceleration is proportional to displacement and directed towards the equilibrium position:

a = −ω²x

The displacement as a function of time (depending on starting position):

x = A cos(ωt) or x = A sin(ωt)

C.2 Wave Model

Intensity of electromagnetic radiation from a point source

At distance r from a source of power P, the intensity is:

I = P / (4πr²)

This is the inverse square law. If you double the distance, the intensity drops to a quarter.

Theme D: Fields

D.2 Electric and Magnetic Fields

Relative permittivity

The permittivity of a medium ε compared to the permittivity of a vacuum ε₀:

εᵣ = ε / ε₀

Electric field between parallel plates

With a potential difference V across plates separated by distance d:

E = V / d

D.4 Induction (HL only)

EMF in an AC generator

The EMF varies sinusoidally. The peak (maximum) value is:

ε₀ = NBAω

The instantaneous value at time t:

ε = ε₀ sin(ωt)

Theme E: Nuclear and Quantum Physics

E.2 Quantum Physics

de Broglie wavelength

All particles have wave-like properties. The de Broglie wavelength λ is:

λ = h / p = h / (mv)

where h is Planck’s constant and p is momentum. This comes up in electron diffraction and other quantum contexts.

E.3 Radioactive Decay

Alpha decay notation

In alpha decay, the nucleus loses 2 protons and 2 neutrons. The mass number decreases by 4, the atomic number decreases by 2:

ᴬ_Z X → ᴬ⁻⁴_{Z-2} Y + ⁴_2 He

Beta-minus decay notation

In beta-minus decay, a neutron becomes a proton. The mass number stays the same, the atomic number increases by 1:

ᴬ_Z X → ᴬ_{Z+1} Y + ⁰_{-1} e + v̄

The antineutrino (v̄) is produced alongside the electron. You need to include it for full marks in decay equation questions.

How to Actually Memorise These

Reading this list is not the same as knowing it.

The most effective approach is to build a set of revision notes for each topic that includes these formulas alongside the ones in the data booklet, so you can see the complete picture. Then practise past paper questions on each topic, with your notes closed. The Exam Pack includes revision note templates for every topic, designed specifically for this.

For the broader strategy around how to turn formula knowledge into exam marks, the how to study IB Physics guide covers the full system.

Get the GradePod Exam Pack for £39 →

Written by Sally Weatherly, IB Physics teacher since 2004, Fellow of the Institute of Physics, and founder of GradePod. I help students work smarter, not harder.