Fieldwork and skills, Year 9

'Does the river flow faster further downstream?'

提示Ask which of the pair you could settle with a stopwatch and a tape measure.

为什么A good enquiry question is narrow enough to be answered by measuring something. 'What is the river like?' has no end: you would not know what to measure or when you had finished. The second question tells you to record speed at several sites and compare them.

A hypothesis

提示It is a prediction you can prove right or wrong with data.

为什么Writing the prediction down before collecting anything keeps an enquiry honest: the data either supports it or does not. A prediction that turns out to be wrong is still a good result, because you have learned something true about the place.

No

提示Read the three speeds in order from source to mouth and see whether they keep climbing.

为什么The speed drops from Site 1 to Site 2, and the last site is still slower than the first, so there is no steady rise. An honest conclusion says the hypothesis was not supported here, then suggests why — perhaps Site 1 was in a narrow, steep stretch.

How the river behaves at other times, such as after heavy rain

提示Think about the same spot in a wet January.

为什么Depth, width and speed all change with the weather and the season, so one visit is a snapshot. Saying so does not weaken a write-up: naming what an enquiry could not show is part of an honest evaluation.

One-off errors are smoothed out, so the result is more reliable

提示Think what a gust of wind or a slip with the stopwatch does to a single timing.

为什么Any single timing can catch an unusual moment. Three or more readings show whether a value was typical, and their average is more likely to come out the same if the work were done again — which is what makes it dependable.

6 cm; 7 cm

提示For the first, share the total equally; for the second, compare the two extremes.

为什么The mean is the total (30 cm) shared between the five pebbles. The range is the largest value minus the smallest, 10 − 3. Quoting both tells a reader the typical size and how spread out the sizes are.

22

提示Put the five counts in order of size first, then find the one in the centre.

为什么In order the counts are 18, 21, 22, 25, 40, and the middle one is the median. The unusually busy count of 40 does not shift it at all, which is why the median is useful when one value is out of line with the rest.

A bar chart

提示The types are separate categories with nothing in between them.

为什么A line joining two points suggests values in between, which makes sense for temperature through a year but not for shop types — there is nothing halfway between 'food' and 'clothing'. Separate bars show separate categories honestly.

A scatter graph

提示Each site becomes a single dot, and you look for a pattern in the cloud of dots.

为什么Plot river depth along one axis and speed along the other, and a cloud of points rising from left to right suggests the two go up together. It shows a link; it does not by itself prove that one thing causes the other.

The single very high reading pulls the mean up

提示Work out roughly where four of the five values sit, then look at the odd one out.

为什么The mean is 62 dB, louder than four of the five readings: one passing motorbike has dragged it upwards. The median, 54 dB, describes the typical level far better, and a good write-up would flag the 96 as an anomaly.

'Most of the shoppers I asked came by car'

提示Pick the claim that stays inside what was actually recorded.

为什么Fifteen out of twenty is three-quarters of your sample, so the narrow statement is true. The wide one stretches twenty Saturday shoppers to cover a whole town, including everyone who was not out shopping that day.