AS Science In Society 1.3 Teacher Notes
Introduction
How Science Works
Aa We can never be sure that an observation is accurate or that a
measurement tells us the ‘true’ value of the quantity we are measuring. We may be influenced by what we expect. Random and/or systematic errors can arise from limitations of the measuring equipment used, or our skill in using it. A single measurement of anything is therefore inherently risky.
Ab If we make repeat measurements of the same quantity, the values are likely to vary. This might be because the quantity we are measuring is changing, or because of measurement error. If errors are random, the average of several measurements is the best estimate of the value of the quantity. The smaller the spread of the measured values and the larger the number of repeat measurements, the more confident we can be that the mean is close to the ‘true’ value. Ad A set of repeat measurements can be summarised by stating an average value and an indication of the spread of values. Useful visual representations are error bars on graph points, and box-and-whisker plots. Ae To judge if there has really been a change in the value of a quantity, we need to take account of both the difference in the mean values and the spread of repeat measurements. It is hard to detect a small change in the mean value of a quantity when the range of values in the data set is greater than the change being detected. Ag Data can be presented and analysed in a variety of formats including graphs with linear scales.
Ah If a measurement is much smaller or larger than the others in a set of repeats, or lies well off a graph line that the others are close to, this may indicate that it is incorrect and should be repeated (if this is possible) or discarded (if it is not).
This activity gives students direct practical experience of some of the issues involved in collecting and analysing data on air
pollution. It is designed to be run over two sessions. In the first session students will make their dust collectors and decide where to place them, and in the second session they will collect and analyse their data.
Resources
Session 1:
• Acetate sheet printed with 2mm graph paper grid - cut into small squares (about 2x2cm)*
• Permanent marker pens for acetate • Double sided sticky tape
• Small plastic bag to put dust collector in (optional) • Map of local area (either printed out or displayed on
whiteboard/OHP) Session 2
• Data analysis worksheet
• Microscopes (or hand lenses if not available)
OR
• Worksheet Ulgham data
The activity
Activity 1
Ask students to discuss, in pairs or small groups, how they would measure the air pollution in their local area. Use prompt
questions such as:
• Will different areas give different readings? What sort of places might they take measurements at?
• Will measurements vary with the weather? With time of day?
• How could they minimise random errors?
Activity 2
Explain to students that they are going to be measuring dust in the air at different places. You could choose to measure around the school site, or ask students to measure in different places around the local area.
Students should assemble their dust collector. On the acetate they will mark a 5 x 5 square, and stick a piece of double sided sticky tape over this area – taking care not to remove both sides of the tape. Place in plastic bag to avoid contamination.
As a group decide where the collectors are going to be placed. You could choose different areas of the school site, or around the local area near students’ homes.
Discuss
• where to put them,
• should they all be the same distance above the ground • should they be sheltered
• how to deal with rain/ adverse weather. • how long to leave them exposed to the air.
This activity works best if there is no rain! Students may need to use sticky tac to keep the detectors from blowing away.
Ask students to predict where they think will be the most and least dusty places – mark on the map, along with the collection points they have chosen.
Students should then take the collectors home, site them as agreed in class and collect dust for the appropriate amount of time. They should then cover the collector with a piece of normal sticky tape and bring back to the next class.
Activity 3
Students now need to obtain data from their dust collector. Using the data analysis worksheet they will use the microscope to count dust particles on each square of their dust collector. They will collate results from the group to produce a graph which shows the number of dust particles at different locations.
You should use this as an opportunity to discuss the nature of data with the students • Why did they have to cover the dust collector with normal sticky tape?
• Were there any outliers?
• Why is it helpful to know both the mean and the range of the data? • Have they measured the ‘true’ value of dust in the area?
• Would their results change if the weather had been different?
• Is the range of values in the data set greater than the difference in dust levels? What does that mean for any conclusions they can draw?
Ask them to look at the prediction made as a class earlier – does their data support the prediction? Can they explain what they have found?
Alternative activity
If it is difficult for students to produce and collect the data, then you can use the alternative worksheet “Ulgham data” which gives dust collection samples for a fictional village to allow students practice in analysing the dust data.
AS Science In Society 1.3 Student Sheets
Introduction
In order to investigate links between health and air quality we need to be able to obtain accurate measurements of different air pollutants in different places. This activity will allow you to collect your own data on dust levels in your local area. You will then analyse the data you and other members of the class have collected.
Making your dust collector.
1. You will be given a small square of acetate which has a grid on it. 2. Using marker pens draw round a 5x5 square as shown. This is your
collecting area.
3. Place a small square of double sided sticky tape over the square. 4. DO NOT remove both sides of the covering.
5. Put your collector in a small plastic bag (if you have been given one).
As a class you will discuss where to place the collectors, how to ensure that you carry out a ‘fair test’, and how long to collect dust for.
6. Place your collector in your agreed position. You may need to use sticky tac to stop it blowing away. Remove the covering from the double sided sticky tape
7.
When your collector has been exposed for the appropriate amount of time, coverthe collecting
area with a normal piece of sticky tape.
Prediction
One important part of carrying out science is making predictions about experiments. As a class you are collect particulate pollution around your local area.
¾ Which area do you think will have the most dust? ¾ Which area do you think will have the least dust? ¾ Why?
Particle collection practical
Data Analysis Worksheet
1. Using a microscope (on low power) or a hand lens look closely at your dust collector. You should see something similar to the diagram below.
We record this data on a grid like this:
2. Record the dust distribution on your dust collector in the grid below.
3. Calculate the mean number of dust particles in a small square.
4. Work out the range of your data
Mean = total number of dust particles on collector = = number of squares on collector
Range = maximum value – minimum value =
5. In order to see whether your prediction from last session was correct you need to compare the results from all of the class.
Make a table with the following columns, and collate the results. Location of dust collector Mean number of dust
particles per small square
AS Science In Society 1.3 Student Sheets
6. Plot the results on a graph showing the mean and the range of the data set.
• Are there any outliers in the data set? If so, do you think that they are due to natural variation in dust levels, or an error in the measurements?
Look back at your prediction from last lesson. • Does your graph back up your prediction?
• Is there a real difference in the measurement of dust particles between the locations in your study? How can you tell?
Particle collection p
ractic
lternative data analysi
a
hree dust collectors around a small village called Ulgham.
s house in a quiet street in the village.
hy?
he following diagrams show the samples that were obtained when the student examined the dust ollectors under a microscope.
mber of dust particles on each dust collector in the grids below.
al
s worksheet
A
Ulgham Dat
A student places t Position 1n a bus stop by the main road into the village. O
Position 2
n the play area in the local park. I
Position 3
laced on wall outside the student’ P
• Which area do you think will show the most particulate pollution? W
T c ecord the nu
Position 2
Position 1
Position 3
RAS Science In Society 1.3 Student Sheets
7. Calculate the mean number of dust particles in a small square.
8. Work out the range of your data
. In order to see whether your prediction from last session was correct you need to compare the
ake a table with
Location of dust collecto
particles per small square
Range Mean = total number of dust particles on collector
number of squares on collector
Range = maximum value – minimum value
9
results from all of the class.
M the following columns, and collate the results. r Mean number of dust Position 1 – main road
Position 2 – play park Position 3 – quiet road
10. Plot the results on a graph showing the mean and the range of the data set.
• Are there any outliers in they are due to natural variation in dust levels,
• Does your graph back u
• Is there a real difference between the locations in your study? How can you tell?
the data set? If so, do you think that or an error in the measurements?
p your prediction?
