Motion

Revise Motion for Physics 1 (IAL) WPH11 (AS Level) — revision notes and instant AI marking.

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Edexcel IAL Physics · Unit: Mechanics

Motion

The Big Idea: Motion is just numbers with direction — if you can keep track of what's a scalar, what's a vector, and pick the right SUVAT equation for what you know and don't know, you can describe any constant-acceleration journey, from a landing plane to a skydiver to a ball thrown at an angle.

Summary — What This Chapter Covers

SUVAT equations — four equations that describe any object moving with constant acceleration.
Motion graphs — displacement-time, velocity-time and acceleration-time graphs, and what their gradients/areas mean.
Slope & area techniques — reading real information off a graph, including curved ones (tangents!).
Scalars vs vectors — the crucial distinction between distance/speed and displacement/velocity.
Resolving vectors — splitting one vector into horizontal and vertical components using trigonometry.
Adding vectors — combining vectors by scale drawing or by calculation.
Components of velocity / projectile motion — treating horizontal and vertical motion completely separately.
Free-body force diagrams — drawing every force acting on an object as a labelled vector arrow.

1. The SUVAT Equations

Imagine you're describing a car journey to a friend, but you can only use five pieces of information: where it started, how fast it started, how fast it ended up, how hard it accelerated, and how long that took. That's exactly what SUVAT gives you — five letters, five variables, and as long as acceleration stays constant, these five numbers completely describe the motion.

The five variables

Symbol	Meaning	Unit
s	displacement	m
u	initial velocity	m s⁻¹
v	final velocity	m s⁻¹
a	acceleration	m s⁻²
t	time interval	s

Important: every one of those except t is a vector — meaning it can be positive or negative depending on direction. Get the signs wrong and your whole answer flips upside down (literally, sometimes).

The Four SUVAT Equations v = u + at s = ut + ½at² s = (v + u)/2 × t v² = u² + 2as

Notice each equation is missing exactly one of the five variables. That's the whole trick to using them — see below.

How to pick the right equation, every time

This is the single most useful skill in this topic. Follow this 3-step routine and you'll never freeze on a SUVAT question again:

List every value the question gives you, using the correct symbol (s, u, v, a, t).
Identify which variable you need to find, and which one is not mentioned at all (not given, not asked for).
Choose the one equation out of the four that doesn't contain that missing variable.

Quick Trick If the object "starts from rest" → u = 0. If it "comes to rest" or "stops" → v = 0. Objects thrown straight up have v = 0 at the very top of their path. These little phrases are the exam's way of quietly giving you a variable for free.

Worked Example — Landing Plane

A pilot is landing a small aircraft. The airstrip is only 450 m long, and the aircraft decelerates from 40 m s⁻¹ at a constant rate of 2 m s⁻². Will the plane stop before it reaches the end of the runway?

Practice Yourself First

Before checking the answer: which SUVAT variables do you have, which is missing, and which equation would you use?

Practice Question

Examiner Tip