Question Constellation Sign up for free AQA · GCSE · Geography · Higher
Evaluating the Downstream Velocity Hypothesis
As part of a physical geography investigation a group of students wanted to test the following hypothesis.
The velocity (speed) of a river increases downstream.
The students used three sites along a river, one kilometre (km) apart. At each site a ball was placed in the centre of the river and the time recorded for it to travel ten metres (m). This was repeated five times at each site. Figure 6 shows the results of this part of the investigation.
| Site A – Upstream | Site B | Site C – Downstream |
|---|---|---|
| 26 | 22 | 20 |
| 24 | 23 | 18 |
| 22 | 18 | 20 |
| 24 | 20 | 18 |
| 25 | 24 | 19 |
To what extent does the data shown in Figure 6 support the original hypothesis?
Use the data in Figure 6 to support your answer.
Write your answer first. You can study the marking guidance whenever you need it.
Study the marking See what earns credit and compare it with a full-mark answer.
Marking points
- 1 Makes a judgement about the extent to which the downstream pattern supports the stated hypothesis.
- 2 Uses accurate Figure 6 data, preferably calculated averages or velocities for Level 2.
- 3 For Level 2, qualifies the judgement using anomalies, overlap, narrow differences or reliability considerations.
Full-mark answer
The data support the hypothesis to a fairly large extent. Mean travel time falls from 24.2 seconds at Site A to 21.4 seconds at Site B and 19.0 seconds at Site C. Using 10 metres divided by mean time, average velocity therefore rises from about 0.41 m/s to 0.47 m/s and then 0.53 m/s downstream. However, the result is not completely conclusive because individual times overlap: 24 seconds occurs at Sites A and B, and 18 seconds occurs at Sites B and C. Only three sites and five repeats were used, so the overall trend supports the hypothesis but the evidence is limited.
Why this answer loses marks
The hypothesis is correct because times generally fall downstream.
This gives a broad judgement but lacks manipulated or comparative evidence and does not qualify the extent using overlap, anomalies or reliability.