IB DP Physics unit plan · SL and HL (2D collisions are HL)
A.2 Dynamics: force, momentum and the laws of motion
Free IB DP Physics unit plan for A.2 Forces and momentum: free-body diagrams, Newton’s laws, impulse, collisions and explosions, circular motion, with ten lessons mapped to 6 hours of theory and 4 hours of practice.
At a glance
- Syllabus
- A.2 · IB DP Physics
- Duration
- 10 hours: 6 theory, 4 practice
- Level
- SL and HL (2D collisions are HL)
- Grade
- DP 1
- Format
- PDF, 7 pages
What the unit does
Forces are treated as interactions and drawn as free-body diagrams. The unit then moves from force to momentum (F = Δp/Δt, impulse as the area under a force–time graph), applies conservation of momentum to collisions and explosions, and ends with circular motion and centripetal force.
Each of the ten learning experiences names the CritABCD lessons to use, the activities and the formative checks. Six one-hour theory sessions are followed by four one-hour practice sessions.
It covers
- Free-body diagrams, resultant force and equilibrium
- Contact and field forces: friction, tension, springs, viscous drag, buoyancy, gravity, electric and magnetic
- Newton’s three laws, momentum and impulse
- Elastic and inelastic collisions, explosions and recoil; two dimensions for HL
- Circular motion: period, angular velocity, centripetal acceleration and force, horizontal and vertical circles
Interactive lessons for this unit
The PDF cites lessons by code (for example A.2 · 1); each one opens the lesson.
- A.2 · 1Newton's first lawThe law of inertia: no net force, no change in motion.
- A.2 · 2Newton's second lawThe law of acceleration: force is the rate of change of momentum.
- A.2 · 3What can a force do?Change the speed, change the direction, change the shape. Then drive a car and see all three.
- A.2 · 4Newton's third lawThe law of action and reaction: forces come in pairs, on different objects.
- A.2 · 5Momentum conservationNewton’s second and third laws together: what one object gains, the other loses.
- A.2 · 6Momentum vs kinetic energyCommonly confused, and once argued over for about sixty years.
- A.2 · 7Momentum change: four casesWhen the direction reverses, treat momentum as a vector. Use a number line.
- A.2 · 8Force: the link between space and timeImbalance drives motion. Force connects the three dimensions of space with time, and carries the present into the future.
- A.2 · 9The four fundamental forcesEvery push and pull in the universe comes down to just four forces. How do they compare?
- A.2 · 10Friction, buoyancy, tension and the restThe everyday forces you name on a free-body diagram, a nitrous drag race, what resists motion, and a skydiver with two terminal velocities.
- A.2 · 11Exam questions: collisions and Newton’s third lawTwo collision problems, worked step by step with our own animated diagram and a recreated momentum-time graph.
- A.2 · 12Free-body diagrams, resultant force and equilibriumDraw every force on one object, find the resultant in one and two dimensions, and decide when the forces balance.
- A.2 · 13Springs, viscous drag and field forcesThe restoring force of a spring, drag on a small sphere in a fluid, and the three field forces: gravitational, electric and magnetic.
- A.2 · 14Impulse: a force acting for a timeImpulse J = FΔt, its link to the change in momentum, the area under a force–time graph, and why a longer contact time means a smaller force.
- A.2 · 15Explosions and recoilBodies pushed apart from rest: the momenta cancel, the lighter body moves faster, and the kinetic energy comes from stored energy.
- A.2 · 16Collisions in two dimensions (HL)Momentum is a vector: conserve it separately along two perpendicular axes, then use the kinetic energy to tell elastic from inelastic.
- A.2 · 17Describing circular motion: period, angular velocity and v = ωrPeriod, frequency, radians and angular velocity, and why a constant speed on a circle still means the velocity is changing.
- A.2 · 18Centripetal acceleration and centripetal forcea = v²/r = ω²r = 4π²r/T², the net force towards the centre, what supplies it, and why “centrifugal force” is a myth.
- A.2 · 19Circular motion in practice: horizontal and vertical circlesCars on bends, a conical pendulum, and a ball on a string in a vertical circle: the forces at the top and the bottom.
- A.2 · 20Exam-style questions: impulse, explosions and circular motionFour worked exam-style problems, then a mixed quiz on impulse, explosions, and circular motion.
- A.2 · QuizQuiz: momentum and forceTen multiple-choice questions on Newton’s second and third laws and on momentum.