Preview
IB DP Physics — Unit A: Space, Time and Motion | SL & HL | A.1 Kinematics
📋 What You Will Learn
- Observe and describe everyday motion using the language of position, displacement, velocity, and acceleration
- Distinguish between scalar and vector quantities and apply this distinction to kinematic variables
- Define displacement, velocity, and acceleration precisely using IB-aligned language and notation
- Derive the equations of uniform acceleration (SUVAT) from first principles using definitions and graphs
- Interpret and analyse displacement–time, velocity–time, and acceleration–time graphs to extract kinematic information
- Apply kinematic equations to solve figure-based and graph-based problems in one and two dimensions
🌍 Real-World Context Watch a sprinter explode out of the starting blocks at the Olympics. In the first two seconds, they go from completely still to nearly 10 m s⁻¹. A few seconds later, they are at full speed and barely accelerating. Near the finish line, they may even slow slightly. Every moment of that race — the burst of speed, the cruise, the slight fade — is described by just three quantities: where the athlete is, how fast they are moving, and how rapidly that speed is changing. These three ideas, position, velocity, and acceleration, are the foundation of all of classical mechanics.
🔍 Guiding Question How can the motion of any object — whether a sprinter, a falling stone, or a planet — be described completely and unambiguously using mathematical quantities, and what do graphs of those quantities reveal about the underlying physics?
Physical Setup and Observation
Consider a ball thrown straight upward from a person's hand. The ball rises, slows to a momentary stop at its highest point, then falls back down, accelerating as it returns. Throughout this entire journey, the ball has a position that changes with time, a velocity that changes in both magnitude and direction, and an acceleration that — perhaps surprisingly — remains constant throughout. This single, simple scenario contains all the key ideas of kinematics.
Notice from the diagram that the velocity arrow changes — it points upward, shrinks to zero, then points downward — while the acceleration arrow remains constant and always points downward. This is a crucial insight: velocity and acceleration are independent quantities that can point in different directions. Understanding this distinction is the first step toward mastering kinematics.
Scalars and Vectors — The Essential Distinction
Before defining the kinematic quantities precisely, we need to understand a fundamental distinction in physics: some quantities are fully described by a number and a unit alone, while others require both a magnitude and a direction. A temperature of 25 °C, a mass of 70 kg, or a time interval of 5 s are complete descriptions — these are scalar quantities. But saying "the car moved 50 m" is incomplete: 50 m in which direction? Quantities that require direction are called vector quantities.
📖 Key Definition — Scalar Quantity A scalar quantity is one that is fully described by a magnitude (size) and a unit only. It has no associated direction. Examples include distance, speed, mass, time, temperature, and energy.
📖 Key Definition — Vector Quantity A