Criterion A rewards physics you can explain and use, not physics you can recite. Examiners want to see the idea, the reasoning that links it to the situation, and units that are right.
You use correct terms and explain why something happens, not just that it happens.
You pick the right idea and use it on a situation you have not seen before.
You weigh data, claims or sources and reach a judgement you can support.
A little of the criterion is addressed. Ideas are basic, partly missing, or not linked to the task.
The main points are there but thin. Some explanations are correct; links to the task or evidence are incomplete.
Mostly accurate, well explained and consistently tied to the task, with only small gaps.
Detailed, precise and justified throughout, with ideas connected and applied to new situations or evidence.
A plain-language guide only. Your teacher marks against the official IB level descriptors.
Explain why a passenger lurches forward when a bus brakes suddenly.
Because of inertia he goes forward.
The passenger and the bus move at the same velocity. When the bus brakes, the braking force acts on the bus, not on the passenger. With no resultant force on him, Newton’s first law says his velocity stays the same, so he keeps moving forward at the old speed while the bus slows. A seat belt supplies the unbalanced force that slows him down with the bus.
Criterion A is Knowing and understanding. It is marked out of 8 across 3 strands (A.i, A.ii, A.iii). Criterion A rewards physics you can explain and use, not physics you can recite. Examiners want to see the idea, the reasoning that links it to the situation, and units that are right.
Name the physical idea first (Newton’s second law, conservation of energy, wave speed) and then use it. For calculations, write the equation, substitute with units, and give the answer with units. In explanations, chain the logic with because and so: cause, mechanism, effect.
Quoting a formula without using it on the situation in the question. Mixing up pairs such as mass and weight, speed and velocity, heat and temperature. Leaving out units, or giving a number with no direction when the quantity is a vector.
Written by CritABCD for study and revision, in our own words. The official MYP Physics guide and assessment criteria are published by the International Baccalaureate. Official IB guide ↗