PHYSICS · Stage 8 · Chapter 6: Forces, Motion and Pressure
Physics 6.5 Presenting data from racing — Interpreting Motion Data
5 min read 6 parts Lesson 5 of 19
Lesson summary
Physics 6.5 Presenting data from racing — Interpreting Motion Data — Alhussan International Academy — Physics (Stages 7–9) notes: Choose the correct type of graph for different types of data and apply ideas about distance-time and speed-time graphs.Categoric variable = a variable…
- Discrete variable
- Continuous variable
- Speed is continuous
- Table and graph
- Reading the line
- Smooth line
Section 1 of 6Types of variable
- Categoric variable a variable whose values are words, such as the name of a driver.
- Discrete variable a variable that can only have certain numerical values, such as a whole number of races won.
- Continuous variable a variable that can take any numerical value, such as time, distance or speed.
Section 2 of 6Choosing a chart or graph
| Type of data | Chart or graph |
|---|---|
| One variable is categoric or discrete | Bar chart or pie chart |
| Both variables are continuous | Line graph, with a smooth line or curve of best fit |
- Pie chart
- Each slice is a fraction of 360°; with 21 equal parts each slice is 360° ÷ 21 = 17.1°.
- Bar chart
- Each bar shows the value for one category, such as the number of races each driver won.
Section 3 of 6Line graph of speed
- Speed is continuous
- The speed of a racing car changes all the time as it accelerates and decelerates.
- Table and graph
- Both show that the speed is changing, but it is easier to see how from the graph.
- Reading the line
- The slope of the line shows the motion.
- A line sloping upwards means the car is accelerating.
- A line sloping downwards means the car is decelerating.
- A flat line means the speed is constant.
- Smooth line
- The line is smooth because speed changes continuously, not suddenly.
- Acceleration
- Read values of speed and time from the axes and use acceleration = change in speed ÷ change in time.
Section 4 of 6Line graph of distance
- Distance is continuous
- It changes all the time, so it is also plotted as a line graph.
- Distance-time graph for a car
- The shape of the line tells the story.
- A horizontal line means the car is stationary.
- A straight sloping line means a steady speed.
- A line that curves upwards means the car is accelerating.
- Speed-time graph for a car
- A horizontal line means a steady speed and a straight sloping line means a steady acceleration.
- Stopping in the pits
- This shows as a flat line on a distance-time graph and as speed zero on a speed-time graph.
Section 5 of 6Gradient and area
| Graph | Gradient means | Area under line means |
|---|---|---|
| Distance-time | Speed | Nothing useful |
| Speed-time | Acceleration | Distance travelled |
Section 6 of 6Good practice in presenting data
- Give each column or axis a title and a unit.
- Choose scales that use more than half of the grid.
- Plot the points accurately.
- Draw a smooth best-fit line or curve for continuous data.
- Look for anomalous results and say whether they might be errors.
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