IB DP Physics-2025-A1.2 Speed & Velocity

IB DP Physics lesson pack on speed and velocity, Topic A.1 Kinematics, SL and HL, first assessment 2025. Teaches rate of change; practises scalar vs vector, km h⁻¹ to m s⁻¹ conversion and vector addition. Editable worksheet, 28-slide lesson deck, teacher key, worked solutions and questions-only assessment, supplied as self-contained HTML plus colour and black-and-white PDFs.

What students learn

Velocity as the rate of change of position. The lesson opens with an F1 car’s quoted top speed of 320 km h⁻¹ and asks what that number says about the car’s motion, and what it leaves out. Students pin down motion as a change in position over time, then meet velocity as the rate of change of position, with its SI unit (m s⁻¹) and its vector character. A margin box unpacks the delta notation and the load-bearing idea of a rate of change (“how much per second?”), and a paired-cars question fixes the one-dimensional sign convention: two cars can share the same speed while their velocities differ in sign. Speed is then defined as the magnitude of the velocity: a scalar, never negative.

Average versus instantaneous values of velocity and speed. A side-by-side comparison sets average speed (total distance over time taken) against average velocity (displacement over time taken) and shows why any path that bends or doubles back makes the average speed come out larger. Students then see how an instantaneous value emerges as the averaging interval shrinks: the reading a speedometer gives at one moment. Two fully worked examples apply journey-totals discipline: a there-and-back car trip whose speedometer reading must first be converted from km h⁻¹ to m s⁻¹, and a circular running track where the athlete’s average velocity for a full lap is zero while her average speed is not. Five exit-ticket multiple-choice questions with full explanations each target a named misconception, from “average velocity zero means the cyclist never moved” to the constant-speed, changing-velocity lap of a circular track and the shrinking-window estimate of an instantaneous speed

• Determine rates of change (taught). The margin box and teacher notes build the “how much per second?” reading of m s⁻¹, and every average speed and average velocity determination in the pack exercises it: the idea acceleration will reuse one level up.
• Identify a quantity as a scalar or vector (practised). The paired-cars question and three of the exit-ticket MCQs turn on telling speed (scalar, never negative) from velocity (vector).
• Apply and use SI prefixes and units (practised). The car-journey example demands a “show that” conversion of a 43 km h⁻¹ speedometer reading to m s⁻¹ before anything can be compared.
• Add and subtract vectors in the same plane (practised). The exam-practice drone flight combines two perpendicular displacement legs by Pythagoras into a 250 m resultant.