Theme A starts with kinematics: describing motion with numbers. Master the four suvat equations and projectiles, and the rest of mechanics builds on them.
Course topics
A · Space, time and motion· Kinematics, forces, momentum, energy, rigid bodies and relativity (HL) · 5 subtopics
Pick the equation that leaves out the quantity you don't know and don't need.
Graphs: gradient of s–t = velocity; gradient of v–t = acceleration; area under v–t = displacement.
Projectiles: split into horizontal (constant velocity, a = 0) and vertical (a = −g = −9.8 m s⁻²). Time links the two.
At the top of a projectile's path, vertical velocity is 0 but horizontal velocity is unchanged (ignoring air resistance).
Worked example
A ball is thrown horizontally at 12 m s⁻¹ from a 20 m cliff. How far from the base does it land? (g = 9.81 m s⁻²)
Vertical: u = 0, s = 20 m, a = 9.81 m s⁻². Use s = ½at².
\(t=\sqrt{\dfrac{2\times20}{9.81}}=\sqrt{4.08}\approx2.02\) s.
Horizontal: no acceleration, so distance = speed × time.
x = 12 × 2.02 ≈ 24.2 m.
Common mistakes
Mixing up sign conventions. Choose up or down as positive and stick to it.
Using suvat when acceleration is not constant.
Putting the horizontal speed into the vertical equations.
Forgetting units and significant figures in the final answer.
Quick check
A car speeds up from 0 to 20 m s⁻¹ in 4 s. What is its acceleration?
5 m s⁻². a = (v − u) / t = 20 / 4 = 5 m s⁻².
An object is dropped from rest. What is its speed after 3 s? (g = 9.8 m s⁻²)
29.4 m s⁻¹. v = u + at = 0 + 9.8 × 3 = 29.4 m s⁻¹.
At the highest point of a projectile's path (no air resistance), which is true?
Vertical velocity is zero, horizontal is unchanged. Gravity only acts vertically. Vertical velocity is momentarily 0; acceleration is still 9.8 m s⁻² downwards.
What does the area under a velocity–time graph represent?
Displacement. Area = velocity × time = displacement.
Practise this in the app. Interactive diagrams, quizzes, exam-style papers with mark schemes and a personal study planner. Open Physics in FortyFive →
FAQ
What topics are in IB Physics?
IB Physics (SL / HL) is organised into: A · Space, time and motion; B · The particulate nature of matter; C · Wave behaviour; D · Fields; E · Nuclear and quantum physics.
Are these IB Physics notes free?
Yes. The topic pages, key terms and the first lesson are free. The full lessons, interactive diagrams and exam-style practice papers with mark schemes are in the FortyFive app, which you can start for free.