NEWTONINE
THE IB PHYSICS LAB
Momentum conservation is a favourite for ‘explain’ and ‘calculate’ questions. In any closed system, total momentum before = total momentum after.
Elastic collisions: objects bounce apart; kinetic energy is conserved.
Inelastic collisions: objects stick together; kinetic energy is not conserved (often transformed into heat/sound).
A typical 6‑mark question: “Use the principle of conservation of momentum to calculate the velocity of the combined cars after the collision.” Always write the full equation, substitute values, and solve.
Always define the positive direction before substituting velocities.
If an object bounces backwards, its final velocity is negative.
Units for momentum are kg·m/s – examiners check them.
For inelastic collisions, mention that kinetic energy is not conserved, but momentum always is.
Impulse = force × time = change in momentum. Crumple zones, airbags, and seat belts increase the time of impact, reducing the average force on the occupants.
MYP often links physics to real‑world applications (Criteria D: Reflecting on the impacts of science). Be ready to explain why an egg dropped onto a pillow doesn’t break, while one dropped onto concrete does – the pillow increases stopping time, reducing force.
In graph questions, impulse is the area under a force–time graph.
When asked to ‘suggest’ or ‘explain’, always connect the science to the safety outcome.
Q1. A 2 kg ball moving at 3 m/s collides with a stationary 1 kg ball. If they stick together, what is their combined velocity?
Q2. Which law explains why a passenger lurches forward when a bus brakes suddenly?
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