Unit Overview
Dynamics
CIE A-Level PhysicsΒ· 5 min read π n/a
1. Unit at a Glance
We build this unit from foundational definitions up to powerful problem-solving tools for interacting objects. We start with core definitions of mass and weight, then move to Newton's laws of motion that describe how forces change motion. From Newton's second law, we derive the concept of linear momentum, then extend this to the conservation of momentum, which we apply to all types of collisions.
This unit is split into 5 connected sub-topics:
Mass and weight
Distinguish between mass and weight, and calculate weight for any given gravitational field strength.
β β± 6 min
Newton's laws of motion
Learn each of Newton's three laws and apply them to solve problems involving force and motion.
β β β± 10 min
Linear momentum
Define linear momentum and relate it to force via the general form of Newton's second law.
β β β± 8 min
Conservation of momentum
Derive and apply the principle of conservation of momentum for isolated systems of interacting objects.
β β β β± 10 min
Collisions
Classify collisions as elastic or inelastic and solve problems for impacts and explosions.
β β β β± 12 min
2. Common Pitfalls
Wrong move:
Confusing mass and weight
Why:
Mass is an invariant property of a body, while weight is a force that changes with gravitational field strength.
Correct move:
Always remember : weight is a force measured in newtons, mass is measured in kilograms.
Wrong move:
Applying conservation of momentum to non-isolated systems
Why:
Momentum is only conserved when no net external force acts on the system of interacting objects.
Correct move:
Check for external forces like friction or gravity before applying the conservation principle.
Wrong move:
Assuming kinetic energy is conserved in all collisions
Why:
Only perfectly elastic collisions conserve kinetic energy; most everyday collisions are inelastic.
Correct move:
Only use kinetic energy conservation when you confirm the collision is explicitly elastic.
3. Quick Reference Cheatsheet
Concept / Formula | Description |
|---|---|
Weight of mass in gravitational field | |
Newton's second law for constant mass | |
Linear momentum of mass moving at velocity | |
General form of Newton's second law | |
Conservation of momentum for isolated systems | |
Defining property of a perfectly elastic collision |
What's Next
Start your learning of this unit with the first foundational sub-topic, Mass and Weight, which introduces core definitions you will use for all subsequent topics on force and momentum in this unit. Once you complete all sub-topics in Dynamics, you can move on to the next unit in the CIE 9702 syllabus.