Diagnostic · Motion in 2D
Projectile & Circular Diagnostic
Maps two-dimensional motion misconceptions — component independence, the centripetal role, the centrifugal ghost — and shows which band your class holds.
IB DP · AP · A-Level · GCSE / IGCSE
1
Forms
30
Questions
32–36
Minutes
11 + 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
Eleven misconception bands across motion in two dimensions.
P1
Component Independence
Horizontal and vertical motion run independently — and independence is two separate claims, not one self-evident fact.
P2
Projectile Acceleration = g Down
In free flight the acceleration is g, straight down, at every instant — including the apex.
P3
Trajectory & Graph-vs-Path
A height–time graph is not the spatial path, and complementary launch angles give equal range at the same speed.
P4
Mass-Independence vs Drag
In vacuum every mass falls with a = g; in air, only object-dependent drag breaks the tie.
C-K1
Circular Acceleration — and Why
At constant speed the velocity still changes direction, so the acceleration is real and points inward — and the reason is kinematic: over a short interval, the change in velocity points to the centre.
C-K2
Period & Angular-to-Linear
Rim speed is circumference over period (v = 2πr/T); angular displacement counts the whole turning history. Provisional-only by design.
C-D0
Curving Needs Inward; Release to Tangent
With no force, motion is straight along the tangent on release — the curved-tube persistence error, the marble expected to keep curving after it exits.
C-D1
Net Inward Force Is a Role — the Keystone
A real, named force — or a component of one — supplies the inward net force; “centripetal” names the role it plays, not an extra force.
C-D2
Vertical Circle & Passive Force
A passive contact force cannot pull: a negative normal force means loss of contact, and at the minimum top speed gravity alone supplies the inward force.
C-D3
No Centrifugal Force
In the ground frame there is no outward force: the passenger continues straight by inertia and the door pushes inward — and the third-law partner of the inward pull acts on the string, not on the object.
C-D4
Banked Curve
Take one axis horizontal toward the centre — the net-force direction; below the design speed, static friction acts up the slope; and the banking angle is mass-independent.
LENS
The Acceleration-Direction Lens
One spine misconception — acceleration points where you're going — tracked across both families.
A question from it
Two-dimensional motion is where good marks most reliably hide the gaps.
The sideways ball stays up longer
Release one ball from rest and launch a second horizontally from the same table height at the same instant.
At the top it stops, so gravity pauses
A stone thrown at an angle reaches the top of its arc.
The fourth arrow
Ask the class to draw every force on a puck whirled on a string in a horizontal circle. Three arrows belong — tension, gravity, the normal force.
Something throws me outward
A car takes a sharp left turn and the passenger is pressed against the right-hand door. Ask what pushed them outward and most students name a centrifugal force.
How it runs
Shared link. No student logins.
30 questions, about 32–36 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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Thank you. We'll set up the Projectile & Circular diagnostic and email you the link within 24 hours.
Grounded in Arons, Knight, Moore and Chabay & Sherwood