IB Physics SL topic guide

Fields

Fields is a core part of IB Physics SL. This guide connects the syllabus ideas behind Gravitational Fields and Forces, Orbital Motion, Electric Fields and Coulomb's Law, Electric Potential and Energy, Magnetic Force and Fields and 1 more units, shows how they appear in worked problems, and points you to the formulas and full lessons needed for exam revision.

What you will learn

Fields syllabus outline

The units below follow the structure used in the full Study to Learn course. Use the outline to identify exactly which idea needs attention, then work through the public example before continuing to the complete lesson path.

D.1

Gravitational Fields and Forces

Newton's Law of Gravitation and Field Strength · Gravitational Potential Energy and Escape Velocity

D.2

Orbital Motion

Orbital Mechanics · Geostationary Orbits and Satellite Applications

D.3

Electric Fields and Coulomb's Law

Coulomb's Law and Electric Fields · Uniform Electric Fields and Parallel Plates

D.4

Electric Potential and Energy

Electric Potential and Potential Energy · Motion of Charges in Electric Fields

D.5

Magnetic Force and Fields

Magnetic Force on Moving Charges · Circular Motion in Magnetic Fields

D.6

Motors and Hall Effect

DC Electric Motor · Hall Effect

Free worked preview

Newton's Law of Gravitation and Field Strength

This complete preview comes from the Gravitational Fields and Forces unit. It introduces the core language, shows the method in context, and gives you a real example of the lesson quality before you create an account.

Gravitational Fields

So far you have treated gravity as a constant downward force near Earth's surface ($g = 9.81$ m s⁻²). This lesson takes the universal perspective: Newton's law of gravitation describes how every mass attracts every other mass across empty space, with a force that weakens as the square of the distance. The concept of a field — a region where a test mass experiences a force — unifies gravity with the electric and magnetic fields coming in D.3–D.5. After this lesson you will calculate field strength at any distance from a spherical mass, and recognise that the $g = 9.81$ you have used all year is simply the special case at Earth's surface.

Every mass exerts an attractive force on every other mass (Newton's Law of Universal Gravitation):

F=Gm1m2r2F = \frac{Gm_1m_2}{r^2}

G = 6.67 × 10⁻¹¹ N m² kg⁻²

Gravitational Field Strength

g=Fm=GMr2g = \frac{F}{m} = \frac{GM}{r^2}

g is the force per unit mass; it equals the acceleration due to gravity. At Earth's surface: g ≈ 9.81 N kg⁻¹ = 9.81 m s⁻².

Field Patterns • Uniform field (near Earth's surface): parallel, equally spaced field lines pointing downward
• Radial field (spherical mass): field lines pointing toward centre; intensity ∝ 1/r²

Gravitational Potential

Vg=−GMrg=−dVgdrV_g = -\frac{GM}{r} \qquad g = -\frac{dV_g}{dr}

Potential is negative (zero at infinity). Potential energy: Ep=mVg=−GMmrE_p = mV_g = -\frac{GMm}{r}

Use the formulas

Keep the data booklet beside you

Revision becomes faster when you practise locating the right equation and understand what every variable means. The full reference is public and searchable on any device.

Open IB Physics SL Data Booklet →

Reviewed by the Study to Learn editorial team · Updated 2026-07-24