Grade 6 · Forces and Motion Basics · Describing Forces
Speed, Distance and Time
Calculating speed and reading motion from a graph.
Learning objectives
- Use the equation speed = distance / time.
- Interpret distance-time graphs.
- Distinguish average speed from instantaneous speed.
NGSS alignment
HS-PS2-1
Analyze data to support the claim that Newton's second law of motion describes the mathematical relationship among the net force on a macroscopic object, its mass, and its acceleration.
MS-PS2-2
Plan an investigation to provide evidence that the change in an object's motion depends on the sum of the forces on the object and the mass of the object.
MYP criteria
- Criterion A — Knowing and Understanding
- Criterion C — Processing and Evaluating
ENGAGE
Who really won the race?
Two students run 100 m. One finishes in 15 s after a slow start and a fast finish; the other keeps a steady pace and finishes in 16 s.
Think about it
- Whose average speed was greater?
- Was the winner ever slower than the other runner?
EXPLAIN
Calculating and graphing speed
Key equation
speed = distance / time. Distance in metres and time in seconds gives speed in metres per second (m/s).
| Journey | Distance | Time | Speed |
|---|---|---|---|
| Walking to school | 900 m | 600 s | 1.5 m/s |
| Cycling | 3000 m | 500 s | 6.0 m/s |
| Sprinting 100 m | 100 m | 12.5 s | 8.0 m/s |
Reading a distance-time graph
- A straight sloping line means constant speed
- A steeper slope means a faster speed
- A horizontal line means the object is stationary
- The gradient of the line equals the speed
Careful
Average speed is the total distance divided by the total time. It is not the average of the individual speeds.
INVESTIGATION
How does slope angle affect speed?
research question
How does the angle of a ramp affect the average speed of a trolley?
hypothesis
A steeper ramp will give a greater average speed because a larger component of weight acts along the slope.
variables
Independent: ramp angle (5, 10, 15, 20, 25 degrees). Dependent: average speed over 1.0 m. Controlled: trolley mass, release point, ramp surface, measuring distance.
method
Release the trolley from rest at the same mark. Time it over a measured 1.0 m and calculate speed. Repeat three times at each angle and take the mean.
safety
Catch the trolley at the end of the ramp. Keep feet clear.
analysis
Plot mean speed against angle. Comment on repeatability using the range of your repeats.
Watch
Motion in a Straight Line: Crash Course Physics
CrashCourse · 9 min
Connects distance, time and speed to graphs.
Before you watch: What does a steeper distance-time graph mean?
- How do you find speed from a distance-time graph?
- Define average speed.
Interactive simulation · PhET
Forces and Motion: Basics
Use the Motion tab. Apply a steady force and watch the speedometer.
While you explore
- How does the speed change with a constant force?
- What happens to the speed when you remove the force and friction is zero?
Key vocabulary
- Average speed
- Total distance divided by total time.
- Speed
- How far something travels each second.
Practice questions
0/2 correct
Level 1 · Criterion A
A runner covers 400 m in 50 s. Their average speed is:
Level 2 · Criterion A
On a distance-time graph, a horizontal line means the object is:
MYP criterion tasks
Level 3 · Criterion C
A student times a trolley over 1.0 m three times: 1.8 s, 1.9 s and 2.4 s. Process this data and comment on its quality.
Reflect & track
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