MYP Physics: Interpreting Motion Graphs — FAQ

It means reading distance-time and velocity-time graphs to describe how an object moves — working out speed, acceleration, direction changes, and periods of rest, without needing the raw data. In MYP 4-5 this sits under Criterion C (Processing and evaluating) and links directly to Newton's laws work later on.

The gradient (slope) of a distance-time graph tells you the speed — steeper means faster. A flat horizontal line means the object has stopped. A curved line means the speed is changing. There's no such thing as a downward-sloping distance-time line for real motion, since distance can't go negative.

On a velocity-time graph, the gradient gives acceleration and the area under the line gives distance travelled. A horizontal line means constant velocity (zero acceleration). A line crossing below zero means the object has reversed direction, not stopped.

A distance-time graph's gradient is speed; a velocity-time graph's gradient is acceleration and its area is distance. Mixing these two up — reading a velocity-time gradient as speed, say — is the single most common error I mark in MYP 4-5 assessments.

Pick two points on the line, then divide the change in distance by the change in time: speed = Δdistance ÷ Δtime. For a straight-line section this gives a constant speed; for a curve you're finding the average speed between those two points, not the instantaneous speed.

Acceleration equals the gradient: divide the change in velocity by the change in time, acceleration = Δvelocity ÷ Δtime, using units of m/s². A negative gradient means deceleration (or acceleration in the opposite direction) — it doesn't automatically mean the object has stopped.

Distance travelled equals the area under the velocity-time line. For a straight horizontal section that's a rectangle (velocity × time); for a sloped section it's a triangle (½ × base × height), and for combined shapes you add the areas together.

The two big ones: reading a velocity-time gradient as if it were speed rather than acceleration, and drawing distance-time graphs that dip downward to show 'returning'. Both come from not checking the axis labels before answering.

Motion graph questions mainly sit under Criterion C: Processing and evaluating, which assesses whether you can present data in graphical form, identify trends, and draw conclusions. They can also appear under Criterion A (Knowing and understanding) when a question asks you to define speed or acceleration directly.

Expect sketch (a rough graph with correctly labelled axes and shape), describe (state what's happening in words — speeding up, constant, at rest), calculate (show working and a numerical answer with units), and deduce (use the graph to reach a conclusion not directly stated).

In the on-screen MYP eAssessment, motion graphs appear as interactive items where you might drag points, read values off a graph, or sketch a rough shape using on-screen tools rather than pencil and paper. The underlying physics tested is identical to classroom assessments.

Solid graph-reading skills at MYP 4-5 feed straight into DP Physics kinematics, where the same gradient-and-area logic reappears with calculus underneath it. Students who can already read velocity-time graphs fluently find the DP jump to acceleration-time graphs and displacement calculus far less daunting.

It's not conceptually difficult, but it's a common stumbling block simply because gradient and area look similar on paper and get confused under exam pressure. Most students who struggle aren't weak at maths — they just haven't had enough repeated practice reading different graph shapes.