Preview
IB DP Physics — Unit A: Space, Time and Motion | SL & HL | A.1 Kinematics
📋 What You Will Learn
- Observe and describe the physical phenomenon of uniform acceleration using real-world examples such as a falling ball or a car accelerating from rest
- Define all key kinematic quantities — displacement, velocity, acceleration, and time — and understand the distinction between scalar and vector quantities
- Derive all four equations of uniformly accelerated motion step-by-step from the definitions of velocity and acceleration
- Apply the equations to solve figure-based and graph-based problems involving objects undergoing constant acceleration
- Analyse displacement–time, velocity–time, and acceleration–time graphs and extract physical information from their gradients and areas
- Evaluate common misconceptions and connect kinematics to Newton's laws, projectile motion, and energy topics across the IB Physics course
🌍 Real-World Context Watch a skydiver the moment they jump from a plane. In the first few seconds — before air resistance becomes significant — they accelerate downward at a nearly constant rate, gaining speed smoothly and predictably. Engineers designing parachutes, safety systems, and landing protocols need to know exactly how fast the skydiver is moving and how far they have fallen at every instant. The same mathematics governs a sprinter launching off the blocks, a spacecraft firing its engines, and a ball rolling down a ramp in a school laboratory. All of these situations share one key feature: the acceleration is constant, and that single fact unlocks a powerful set of equations that can describe the entire motion.
🔍 Guiding Question How can we use the definitions of displacement, velocity, and acceleration to derive a complete set of equations that describe any motion with constant acceleration — and how do the graphs of these quantities reveal the underlying physics?
Physical Setup and Diagram
Consider a ball released from rest at the top of a smooth ramp inclined at a fixed angle. As the ball rolls down, it moves faster and faster — it is accelerating. Crucially, because the ramp angle is fixed and the surface is smooth, the component of gravity acting along the ramp is constant throughout the motion. This means the rate at which the ball gains speed is also constant: the acceleration does not change as the ball moves. This is the defining feature of uniformly accelerated motion.
Notice in the diagram that the component of gravity along the slope, \( mg\sin\theta \), is the same at every point along the ramp because \( \theta \) is fixed. This constant net force produces a constant acceleration down the slope. The velocity arrows grow longer at each successive position, but they grow at a steady rate — this is the visual signature of uniform acceleration.
Core Concepts and Definitions
Before we can write any equations, we need to be precise about what we mean by the quantities involved. In everyday language, "speed" and "velocity" are often used interchangeably, but in physics they are distinct. Similarly, "distance" and "displacement" carry different meanings. Getting these definitions right is not just a formality — the equations we derive will only work correctly if we apply them with the right quantities and the right signs.
📖 Key Definition — Displacement Displacement, \( s \), is the change in position of an object in a specified direction. It is a vector