1.2.4Motion, Forces and Energy
Speed-Time Graphs — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions
5 min read 7 parts Lesson 15 of 91 1 quiz
Lesson summary
1.2.4 Speed-Time Graphs — IGCSE Physics Notes — IGCSE PHYSICS notes: Describe motion from speed-time graphs and find distance from the area under the graph.LineMeaningHorizontal at zeroStationaryHorizontal above zeroConstant speed, zero accelerationStraight upward slopeConstant p…
- Positive gradient
- Negative gradient
- Total distance
- Part of a journey
- Mixed shapes
- Area under graph
Part 1 of 5Reading speed-time graphs
| Line | Meaning |
|---|---|
| Horizontal at zero | Stationary |
| Horizontal above zero | Constant speed, zero acceleration |
| Straight upward slope | Constant positive acceleration |
| Straight downward slope | Constant deceleration |
| Steeper slope | Greater acceleration |
Part 2 of 5Gradient
Meaning
- Meaning the gradient of a speed-time graph is the acceleration
Positive gradient
- Positive gradient speed increases
Negative gradient
- Negative gradient speed decreases
Part 3 of 5Plotting a speed-time graph
1
Label the x-axis with time and the y-axis with speed.
2
Choose sensible scales so the graph fills more than half of the grid.
3
Plot the points from the data.
4
Join with horizontal lines for constant speed and sloped lines for changing speed.
Part 4 of 5Distance from the area
1Area under the graph
- Area under the graph it represents the distance travelled
2Triangle
- Triangle area = ½ × base × height
3Rectangle
- Rectangle area = base × height
4Total distance
- Total distance find the total area under the graph
5Part of a journey
- Part of a journey find the area for the chosen time interval only
6Mixed shapes
- Mixed shapes split the area into triangles and rectangles and add them
Part 5 of 5More from the specification
More from the specification
Interpreting Distance-Time and Speed-Time Graphs
- On a distance-time graph, the gradient represents speed,
- whereas on a speed-time or velocity-time graph, the gradient represents acceleration and the area under the line equals the distance travelled by the object.
Velocity as a Vector Quantity
- Velocity represents the rate of change of displacement and includes direction;
- opposite directions of moving objects are assigned opposite mathematical signs.
Forces and Terminal Velocity
- When an object falls, downward gravitational weight initially exceeds upward air resistance;
- as speed increases, drag increases until resultant force equals zero,
- resulting in a constant average terminal velocity.
Gravitational field
- Region where mass experiences gravitational force.
Field strength
- G = Fg/m.
Velocity
- Rate of change of displacement.
Resistance
- Opposition to current, R = V / I, in ohms (Ω).
Weight
- Gravitational force on a mass.
Terminal
- Connection point of a cell, labelled + or −.
Distance-time graph
- Graph of distance against time showing movement.
Average speed
- Total distance divided by total time.
Terminal velocity
- Constant speed when air resistance equals weight.
Resultant force
- Another name for net force.
Key terms
| Term | Meaning |
|---|---|
| Speed-time graph | Graph of speed against time. |
| Gradient | Acceleration on a speed-time graph. |
| Area under graph | Distance travelled. |
| Constant acceleration | Straight sloping line. |
| Deceleration | Negative acceleration. |
| Base | Time width of a section. |
Avoid these mistakes
1
Thinking a horizontal line means stationary on a speed-time graph — it means constant speed.
2
Using the gradient for distance — the gradient gives acceleration and the area gives distance.
3
Forgetting the ½ for a triangle — area = ½ base × height.
4
Using the whole area for a time interval — use only the section in the interval.
Marked practiceQuizzes for this lesson
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