In simple terms
A friendly intro before the formal notes — no formulas yet.
Equations of motion
Cambridge 9702 Paper 2 — Equations of motion (2.1). Senpai Corner diagram-backed pilot with premium structure and live visuals.
- 1
Speed is the total distance travelled per unit time (a scalar quantity).
- 2
Velocity is the rate of change of displacement (a vector quantity). The sign (+ or -) indicates direction.
- 3
Acceleration is the rate of change of velocity (a vector quantity).
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Example: If 'up' is the positive direction, an object moving upwards at 5 m/s has a velocity of +5 m/s. An object moving downwards at 5 m/s has a velocity of -5 m/s. Both have a speed of 5 m/s.
What this topic covers
The official Cambridge syllabus points this lesson works through.
- 2.1.1
Define and use distance, displacement, speed, velocity and acceleration
- 2.1.2
Use graphical methods to represent distance, displacement, speed, velocity and acceleration
- 2.1.3
Determine displacement from the area under a velocity-time graph
- 2.1.4
Determine velocity using the gradient of a displacement-time graph
- 2.1.5
Determine acceleration using the gradient of a velocity-time graph
- 2.1.6
Derive, from the definitions of velocity and acceleration, equations that represent uniformly accelerated motion in a straight line
- 2.1.7
Solve problems using equations that represent uniformly accelerated motion in a straight line, including the motion of bodies falling in a uniform gravitational field without air resistance
- 2.1.8
Describe an experiment to determine the acceleration of free fall using a falling object
- 2.1.9
Describe and explain motion due to a uniform velocity in one direction and a uniform acceleration in a perpendicular direction
Explore the concept
Use the live diagram and synced steps — play it or tap a step card to walk through.
Trajectory Horizontal and vertical motion combine into a parabola; scrub time to fly it.
67 more simulations for this topic — run them in the Simulations section below
Simulations
Every simulation here runs the real model — try the steps on a card, then check what you see against the notes.
67 simulations · 5 to start with
Start herein this order — each one shows a different piece of the topic
- The Physics ClassroomStart here · 19702 2.1 · IB A.1
Kinematic Graphing
A moped leaves a trail of dots; set the initial velocity, acceleration and time and watch the position-, velocity- and acceleration-time graphs
Why this one: Set u, a and t for the moped and watch the dot spacing, the s–t curve and the v–t line grow together: SUVAT on screen.
Try this
- Set the acceleration to zero and read the three graphs.
- Add a positive acceleration and compare the dot spacing.
- Give the initial velocity and acceleration opposite signs.
Look for The gradient of the position-time graph equals the value shown on the velocity-time graph.
Physics Interactives by The Physics Classroom · Licensed to MarkScheme (site terms otherwise permit linking only)
- 3JCN PhysicsStart here · 29702 2.1 · IB A.1
Linear Motion – Graphs of x, v, and a
Set velocity and acceleration for linear motion; read x-t, v-t and a-t graphs
Why this one: Constant a turns the x–t graph into a parabola and the v–t graph into a straight line of gradient a.
Try this
- Set a velocity with zero acceleration and read the x-t graph.
- Add a positive acceleration and compare the x-t and v-t graphs.
- Set a negative acceleration and compare.
Look for Constant velocity gives a straight x-t line; constant acceleration gives a parabola in x-t and a straight v-t line.
3JCN Physics Simulation by Thomas Nguyen · CC BY 4.0
- oPhysicsStart here · 39702 2.1 · IB A.1
1D Kinematics: Velocity vs. Time Graph
Shape a straight-line v-t graph by dragging points; read off displacement, acceleration and motion
Why this one: Drag the v–t line and read displacement as the signed area and acceleration as the gradient.
Try this
- Drag the points to make a constant positive velocity and read the displacement.
- Make the line slope down through zero velocity.
- Make the line steeper and read the acceleration.
Look for Displacement is the signed area under the v-t line and acceleration is its gradient.
Simulation by Tom Walsh, oPhysics.com — made with GeoGebra · Licensed to MarkScheme (site: free for non-profit educational use; applets made with GeoGebra)
- PhETStart here · 49702 2.1
Projectile Motion
Fire a cannon with chosen speed and angle; trace the path with or without air resistance.
Why this one: Switch on velocity vectors: the horizontal arrow never changes while the vertical one grows by g each second.
Try this
- Set 15 m/s at 45° with air resistance off — note the range, then try 30° and 60°.
- Fire horizontally from height; use the tape to check s = ½gt² for the drop.
- Turn on velocity vectors — the horizontal arrow never changes.
Look for Horizontal velocity is constant; vertical motion is uniform acceleration g — equal ranges at complementary angles.
Simulation by PhET Interactive Simulations, University of Colorado Boulder · Licensed to MarkScheme (public licence CC BY-NC 4.0 since 2026-03-30)
- The Physics ClassroomStart here · 59702 2.1 · IB A.1
Graph That Motion
Match 11 animated motions to their position-time and velocity-time graphs
Why this one: Match a moving object to its s–t and v–t graphs; a curving s–t pairs with a sloping v–t.
Try this
- Watch a motion and choose its position-time graph.
- Choose its velocity-time graph.
- Check and move to the next motion.
Look for A curved position-time graph pairs with a sloping velocity-time graph.
Physics Interactives by The Physics Classroom · Licensed to MarkScheme (site terms otherwise permit linking only)
More simulations62 more on this topic — core ones first
- PhETCoreJava · best on a laptop9702 2.1
The Moving Man
Drag the man along the line, or type in position, velocity and acceleration, and watch all three graphs update together.
Try this
- Drag the man at a steady walk — the velocity graph is flat.
- Set an acceleration and play — the position graph curves.
- Walk left then right — note where velocity crosses zero.
Look for Gradient of x–t is v; gradient of v–t is a; turning points of x are where v = 0.
Simulation by PhET Interactive Simulations, University of Colorado Boulder · Licensed to MarkScheme (public licence CC BY-NC 4.0 since 2026-03-30)
- oPhysicsCore9702 1.4 · 9702 2.1 · IB A.1
Relative Velocity: Boat Crossing a River
Set boat heading, boat speed and river speed; watch the resultant path across the river
Try this
- Point the boat straight across with the river flowing and watch the path.
- Angle the heading upstream until the path is straight across.
- Set the river speed equal to the boat speed and try to cross directly.
Look for The boat’s path follows the vector sum of boat velocity and river velocity, so heading and path differ whenever the river flows.
Simulation by Tom Walsh, oPhysics.com — made with GeoGebra · Licensed to MarkScheme (site: free for non-profit educational use; applets made with GeoGebra)
- oPhysicsCore9702 2.1 · IB A.1
Uniform Acceleration in One Dimension: Motion Graphs
Adjust initial position, velocity and acceleration; watch the motion and its x-t, v-t, a-t graphs together
Try this
- Set acceleration to zero and a positive initial velocity; compare the three graphs.
- Give a positive initial velocity and a negative acceleration.
- Set initial velocity to zero and vary only the acceleration.
Look for The v-t gradient equals the a-t value and the x-t gradient equals the v-t value, so a straight v-t line pairs with a parabolic x-t curve.
Simulation by Tom Walsh, oPhysics.com — made with GeoGebra · Licensed to MarkScheme (site: free for non-profit educational use; applets made with GeoGebra)
- oPhysicsCore9702 2.1 · IB A.1
Position, Velocity, and Acceleration vs. Time Graphs
Slide points on a v-t graph; the x-t and a-t graphs update to match the motion
Try this
- Slide the v-t points to make a horizontal line and look at the x-t graph.
- Make the v-t line slope upward through zero.
- Make a v-t segment slope downward and check the sign on the a-t graph.
Look for Where the v-t line crosses zero the x-t graph turns around, and the a-t value is the v-t gradient.
Simulation by Tom Walsh, oPhysics.com — made with GeoGebra · Licensed to MarkScheme (site: free for non-profit educational use; applets made with GeoGebra)
- oPhysicsCore9702 2.1 · IB A.1
Kinematics Graphs: Adjust the Acceleration
Set initial position/velocity then adjust acceleration; see x-t, v-t and a-t graphs of the object
Try this
- Set initial velocity positive and acceleration zero, then run.
- Keep the same initial velocity and set a negative acceleration.
- Double the acceleration and compare the v-t slopes.
Look for Doubling the acceleration doubles the v-t gradient and makes the x-t parabola curve more tightly.
Simulation by Tom Walsh, oPhysics.com — made with GeoGebra · Licensed to MarkScheme (site: free for non-profit educational use; applets made with GeoGebra)
- oPhysicsCore9702 2.1 · IB A.1
Uniform Acceleration in One Dimension
Adjust x0, v0 and a for a car under uniform acceleration; run and watch the resulting motion and data
Try this
- Set v0 positive and a = 0, then run.
- Set v0 positive and a negative, run, and watch the car reverse.
- Set v0 = 0 and compare runs at two values of a.
Look for With v0 and a of opposite sign the car slows, stops momentarily and returns; the data follow v = v0 + at.
Simulation by Tom Walsh, oPhysics.com — made with GeoGebra · Licensed to MarkScheme (site: free for non-profit educational use; applets made with GeoGebra)
Key formulas
Tap any symbol to reveal exactly what it means and its units.
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Full topic notes
Formal explanation with the rigour you need for the exam.
Understanding Key Terms: Scalars & Vectors
In physics, how we describe movement matters. Displacement () is a vector quantity, telling you the straight-line change in position from start to end, including direction. Velocity () is also a vector; it's the rate at which displacement changes. Acceleration (), another vector, is the rate at which velocity changes. Always consider the direction for these quantities!
Velocity: Acceleration:
Speed is the total distance travelled per unit time (a scalar quantity).
Velocity is the rate of change of displacement (a vector quantity). The sign (+ or -) indicates direction.
Acceleration is the rate of change of velocity (a vector quantity).
Example: If 'up' is the positive direction, an object moving upwards at 5 m/s has a velocity of +5 m/s. An object moving downwards at 5 m/s has a velocity of -5 m/s. Both have a speed of 5 m/s.
The SUVAT Equations: Your Toolkit for Motion
When an object moves with uniform (constant) acceleration, we can use a set of four powerful equations to link its motion variables. These are commonly known as the SUVAT equations, named after the quantities they relate: displacement (), initial velocity (), final velocity (), acceleration (), and time (). Mastering these is crucial for exam success.
Always list your knowns () and what you need to find.
Select the SUVAT equation that includes these variables and excludes the one you don't know or need.
Remember to assign a consistent positive direction; negative values will indicate the opposite direction.
If an object starts from rest or is dropped, its initial velocity () is .
Motion Under Gravity: Special Cases
A common scenario for uniform acceleration is objects moving under gravity. Near Earth's surface, the acceleration due to gravity () is approximately downwards. This value is constant for objects in free fall (ignoring air resistance) and is crucial in many problems.
When dealing with vertical motion, always establish a positive direction (e.g., upwards or downwards) and stick to it! If upwards is positive, then 'g' will be for an object falling down.
Graphical Analysis of Motion
Graphs provide a powerful visual representation of motion. A displacement-time graph shows an object's position over time, where its gradient reveals the object's velocity. A velocity-time graph illustrates how velocity changes over time; here, the gradient gives the acceleration, and the area under the graph provides the total displacement. Curved lines on a velocity-time graph indicate non-uniform acceleration.
Displacement-time graph: Gradient = velocity.
Velocity-time graph: Gradient = acceleration.
Velocity-time graph: Area under curve = displacement.
A straight line on a velocity-time graph means uniform acceleration.
A horizontal line on a velocity-time graph means constant velocity (zero acceleration).
Motion in Two Dimensions: Projectile Power!
When an object, like a thrown ball, moves in two dimensions (e.g., horizontally and vertically), we call this projectile motion. The key insight here is that the horizontal and vertical components of motion are entirely independent of each other. This means you can apply the SUVAT equations separately to each direction. To do this, you first resolve the initial velocity into its horizontal and vertical components using trigonometry.
Horizontal motion: Constant velocity (assuming no air resistance), so acceleration .
Vertical motion: Uniform acceleration due to gravity, downwards.
The time () is the only variable common to both horizontal and vertical components.
For projectile motion, break the initial velocity into horizontal and vertical components using trigonometry. Treat each component as a separate 1D problem, but remember they share the same time of flight!
Worked examples
See the formulas applied — reveal one step at a time, like the exam.
A car accelerates uniformly from rest to a speed of in . Calculate the distance it travels during this time.
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Identify knowns:
A ball is thrown vertically upwards from the ground with an initial speed of 15.0 m/s. Ignoring air resistance, calculate the maximum height it reaches. (Take g = 9.81 m/s²)
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Define direction and list knowns: Let's define the upward direction as positive.
How it all connects
The big idea sits in the middle — tap a linked idea to explore the link.
Tap a linked idea to see how it connects back to the main topic — that connection is what examiners reward.
Glossary
Key terms for this topic — skim now; the Check step will test them.
- v–t area
The total displacement of the object.
- typical initial velocity
- Displacement ()
The overall change in position from a starting point, including direction (a vector quantity).
- s–t gradient
The object's velocity.
- Scalar or vector?
Velocity is a vector quantity (it has both magnitude and direction).
Quick check
Write your answer first, then compare it with the model one — the gap is what you would have lost.
Teach it back
If you can explain it simply, you own it — gaps here are marks you’d lose.
Teach it back
Explain this topic as if teaching a friend. We name the gaps an examiner would still dock.
Revision flashcards
Guess first, then flip — retrieval beats re-reading.
Key takeaways
Review these before you close the topic — retrieval beats re-reading.
Speed is the total distance travelled per unit time (a scalar quantity).
Velocity is the rate of change of displacement (a vector quantity). The sign (+ or -) indicates direction.
Acceleration is the rate of change of velocity (a vector quantity).
Example: If 'up' is the positive direction, an object moving upwards at 5 m/s has a velocity of +5 m/s. An object moving downwards at 5 m/s has a velocity of -5 m/s. Both have a speed of 5 m/s.
Practice — then mark it
The whole point: a real Cambridge question, marked mark-by-mark.
Determine the vertical distance travelled by the object.
By drawing a suitable line on Fig. 2.1, determine the acceleration of the skydiver at time t = 9.0 s.
acceleration = .............................................................. ms-2
Extra simulations & links
PhET, GeoGebra and other curated tools — open in a new tab.
Frequently asked
Checkpoint
One marked question is worth ten re-reads — close the loop before you move on.
Reading it isn’t knowing it — prove it.
Before you move on: do 9702/23 · Q2(b)(ii) on paper, snap a photo, and get examiner-style feedback on exactly where you win and lose marks.
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