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Unit 3: Forces, motion and pressure

Describing movement — HIA International - Grade 7 Revision Notes & Topical Questions

5 min read 9 parts Lesson 4 of 8 3 quizzes

📚 HIA International - Grade 7 Hub / Topical Revision
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Lesson summary

3.3 Describing movement — HIA INTERNATIONAL notes: Describe the movement of an object using a distance-time graph and calculate speed from it.Distance-time graph = a graph with distance travelled on the vertical axis and time on the horizontal axis.Advantages over words.It is eas…

  • Stationary
  • Steeper line
  • Shallower line
  • Sketch graph
  • Graph with values
  • Average speed

Part 1 of 7Why use distance-time graphs

Distance-time graph
Distance-time graph a graph with distance travelled on the vertical axis and time on the horizontal axis.
Advantages over words.
  • It is easier to see trends and patterns.
  • You can read any value of distance or time during the journey.
  • Other values, such as speed, can be calculated from it.
  • Information about the whole journey can be seen at once.

Part 2 of 7Sections of a journey

SectionGraph shapeMeaning
At the startDistance is zeroNo distance travelled yet
Moving at constant speedStraight upward sloping lineSame distance travelled each second
StationaryHorizontal lineSpeed is zero, but time still passes
Faster constant speedSteeper upward sloping lineGreater distance each second
Returning to the startStraight downward sloping lineDistance from the start decreases

Part 3 of 7Stationary objects

Stationary
Stationary not moving, with a speed of zero; also called at rest.
Graph
  • Graph a horizontal line, because distance does not change while time passes.

Part 4 of 7Comparing speeds on a graph

Steeper line
  • Steeper line faster speed.
Shallower line
  • Shallower line slower speed.
Direction
  • Direction upward slope means moving away, downward slope means returning.

Part 5 of 7Sketch graphs and graphs with values

Sketch graph
  • Sketch graph has no numbers on the axes.
Graph with values
  • Graph with values read the distance from the vertical axis and the time from the horizontal axis.
Speed
  • Speed speed = distance ÷ time, using the section of the graph you want.
Average speed
  • Average speed total distance ÷ total time.

Part 6 of 7Drawing a distance-time graph

1
Plot time on the horizontal axis and distance on the vertical axis, with units.
2
Mark the points from the measurements.
3
Join them with ruled straight lines for constant speeds.
4
Label each part of the journey.

Part 7 of 7Investigating walking and running

1
Plan which measurements to take and how to take them.
2
List safety precautions for the person who is running.
3
Measure the distance and the time for walking and for running.
4
Calculate each average speed in m/s.
5
Plot both on one distance-time graph and label the lines.
  • Result
    • the running line is steeper because more distance is covered in the same time.

Key terms

TermMeaning
Distance-time graphA graph showing how distance changes with time.
StationaryNot moving.
Constant speedA speed that does not change.
Average speedTotal distance divided by total time.
SpeedDistance travelled per unit of time.
At restAnother way of saying stationary.
Sketch graphA graph drawn without numbers on the axes.
GradientThe steepness of a line.

Avoid these mistakes

1
Putting distance on the horizontal axis — time goes on the horizontal axis.
2
Saying a flat line means moving slowly — it means stationary.
3
Saying a downward line means slowing down — it means returning to the start.
4
Reading speed from the height of the line instead of its steepness.

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