Chapter P4: Explaining motion

Chapter P4: Explaining motion is a core topic in OCR GCSE Combined Science that introduces the fundamental principles of how and why objects move. You'll explore key concepts like speed, velocity, acceleration, and the relationship between force and motion, as described by Newton's laws. This chapter builds on earlier ideas about forces and energy, giving you the tools to analyse real-world scenarios such as cars braking, objects falling, or athletes sprinting. Understanding motion is essential not only for exams but also for grasping more advanced topics in physics, including momentum and energy transfers.

In this chapter, you'll learn to interpret distance-time and velocity-time graphs, calculate average speed and acceleration, and apply Newton's first and second laws to explain changes in motion. You'll also investigate the effect of forces like friction and air resistance, and how they affect stopping distances. Practical skills are emphasised, including using ticker timers or light gates to measure motion accurately. By the end, you should be able to predict how an object will move when forces are applied, and explain everyday phenomena like why passengers lurch forward in a braking car.

This topic is assessed in both the multiple-choice and structured questions of your Combined Science exams, often in contexts like road safety or sports. Mastering P4 gives you a strong foundation for later topics such as momentum (P5) and energy (P6). It also develops your ability to use mathematical formulas and interpret graphical data—skills that are valuable across all sciences. Make sure you're comfortable with rearranging equations and drawing accurate graphs, as these are common sources of marks.