Diagnostic · Impulse & collisions
Momentum Diagnostic
Maps what impulse, conservation and the system boundary mean to your students — including the compensation lens — and shows which band to address first.
IB DP · AP · A-Level · GCSE / IGCSE
1
Forms
24
Questions
25–30
Minutes
9 + lens
Bands
Run in classrooms at 7 schools · 7 countries · 3 continents
The wrong ideas are not ours. Physics education research has documented them since 1979 — Viennot · Trowbridge & McDermott · Hestenes · Maloney. Every diagnostic is built on them.
What it maps
Nine misconception bands plus a cross-cutting lens.
I1
Impulse Delivers a Change
“The new momentum equals the impulse” — dropping the momentum already carried. The force-time area; the same-force-same-time comparison.
CS1
Conservation, Transfer & the System Boundary
Momentum transferred, not destroyed, within a chosen system: the wall bounce, mass-blind recoil from rest, and the internal spring that cannot move the centre of mass.
CS2
Conditions for Conservation
“Always conserved” and its mirror image: the braking car's large external impulse; gravity's negligible impulse over a brief mid-air collision.
N3
Reciprocity
Equal-and-opposite forces and momentum changes with unequal velocity changes: the cannon comparison, and internal-force self-propulsion at the dashboard.
V1
Vector Momentum & Sign
Momentum as a signed vector: the same-speed reversal whose momentum change is about 2 m v, not zero; the sign of the momentum change versus the sign of the kinetic-energy change.
V2
Two-Dimensional Conservation
Component-by-component conservation in an off-centre collision; the 90-degree result for an equal-mass elastic collision. A two-item, lower-confidence band.
COL1
Elastic vs Inelastic: What's Conserved
The collision-cluster keystone: sticking does not destroy momentum; conserved momentum is not conserved speed; momentum yes, kinetic energy no.
COL2
Underdetermined Collisions
Momentum conservation alone is one equation with two unknown final velocities — it constrains a collision but cannot finish it. A two-item, lower-confidence band.
COL3
Clay vs Rubber
A bounce delivers about twice the impulse of a stop — about m v versus about 2 m v. The tip-the-block comparison. A two-item, lower-confidence band.
L-COMP
The Compensation Lens
Fires only when both faces of the compensation error are selected together — “the bigger mass takes a bigger momentum change” with “equal forces mean equal speeds.” Reported as a cohort percentage, never as a band — and remediated first when it fires.
A question from it
Momentum hides behind the conservation slogan.
The push becomes the momentum
A cart already carries 6 kg m/s of momentum and receives a 4 N s impulse along its motion.
“Always conserved” — and its mirror image
A car brakes to a stop.
Conserved momentum, unchanged speed
A 1 kg cart at 6 m/s couples to an identical cart at rest.
Same push, so same speed
The same constant force acts for the same time on a cart of mass m and a cart of mass 2m, both starting from rest.
How it runs
Shared link. No student logins.
24 questions, about 25–30 minutes, no calculator required, single sitting.
The report arrives within 48 hours of your class finishing.
Request
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Founding-department programme opens January 2027
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Grounded in Arons, Knight, Moore and Chabay & Sherwood