Unit Overview

Space, time and motion

IB Physics SL· 5 min read 📊 20-22% of overall IB Physics SL exam

1. Unit at a glance

This unit follows a logical learning arc: you will start by describing motion without considering its causes (kinematics), then move to what causes changes in motion (forces and momentum), next explore energy transfers that accompany motion, and finally apply all previous concepts to curved and orbital motion.

Concepts from this unit are tested across both Paper 1 (MCQ) and Paper 2 (structured response) of the IB Physics SL exam, and are required for all subsequent units in the syllabus.

The unit is split into 4 core sub-topics:

Kinematics

Describes motion in 1 and 2 dimensions using displacement, velocity, acceleration and kinematic equations.

★★⏱ 15 min

Forces and momentum

Covers Newton's laws of motion, free-body diagrams, impulse, and conservation of momentum for collisions.

★★★⏱ 20 min

Work, energy and power

Introduces work done, energy conservation, kinetic/potential energy, and power calculations.

★★⏱ 15 min

Circular motion and gravitation

Applies previous concepts to uniform circular motion, Newton's law of gravitation, and orbital motion.

★★★★⏱ 18 min

2. Common Pitfalls

Wrong move:

Mixing up scalar and vector quantities when adding or resolving motion components

Why:

Vectors require direction when combining, while scalars only add numerically regardless of direction

Correct move:

Always resolve vectors into perpendicular x/y components before combining or calculating results

Wrong move:

Treating centripetal force as an extra separate force acting on a rotating object

Why:

Centripetal force is the net resultant force towards the center of rotation, not an additional force

Correct move:

Draw all individual acting forces first, then calculate the net force that acts as centripetal force

Wrong move:

Applying conservation of momentum/energy without checking for external forces

Why:

External forces change total momentum and do work that changes total mechanical energy

Correct move:

Confirm the system is closed (no net external force) before applying conservation laws

3. Quick Reference Cheatsheet

Concept	Key Formula/Rule
SUVAT (constant acceleration)	$v = u + a t$ , $s = u t + \frac{1}{2} a t^{2}$ , $v^{2} = u^{2} + 2 a s$
Newton's Second Law	$F_{n e t} = ma = \frac{Δ p}{Δ t}$
Conservation of Momentum	$\sum p_{ini t ia l} = \sum p_{f ina l}$
Work done	$W = F s cos θ = Δ E_{k}$
Conservation of Mechanical Energy	$Δ E_{k} + Δ E_{p} = 0$ (no resistive forces)
Centripetal acceleration	$a_{c} = \frac{v ^{2}}{r} = ω^{2} r$
Newton's Law of Gravitation	$F = G \frac{M _{1} M _{2}}{r ^{2}}$
Orbital speed	$v = \frac{GM}{r}$

What's Next

Begin your study of this foundational unit with the first sub-topic on Kinematics, where you will master the core definitions and equations needed to describe motion in 1D and 2D. This knowledge will underpin every subsequent sub-topic in this unit. Once you complete all four sub-topics here, you can move on to the next core IB Physics SL unit on Thermal Physics.