Teaching notes
Read before the lesson. Hidden from students when teacher mode is off.
Why steel wool and not nails
A nail exposes about 1.3 cm² of steel per gram. Steel wool grade 0000 exposes around 200 cm² per gram — roughly 160 times more surface. What takes a nail five weeks takes steel wool one lesson.
A short vinegar soak strips the protective oxide layer so the reaction starts immediately rather than after a delay. Rust is then visible within about twenty minutes, and the pads keep going over the following week for a second reading at the start of Lesson 7.
It is worth the bench space because it turns "it got hot" from the Lesson 1 criteria list into a number, and because some students will not believe rusting is a reaction until they see the temperature move.
The one instruction that matters most
Resist rescuing
A group whose method fails has generated genuine evidence for the evaluation criterion. Note what happened, let it run, and make sure they write it down as it happens. The written account of what went wrong is worth more in CP3 than a tidy result — and a group you quietly fixed has learnt nothing and given you nothing to assess.
The exception is safety. Step in immediately for anything unsafe, without discussion.
Running the observation grid
- One page per group, on a clipboard. Print before the lesson with names filled in.
- You are looking for four things: the safety statement before equipment is issued, whether the method is actually followed, precision of measurement and recording, and what they do when something goes wrong.
- Note evidence, not ratings, while you circulate. "Read 2.3 not 2.30, corrected when asked" is usable later. A circled letter with no note is not.
- Rate afterwards, once you have the whole picture. Trying to grade live means missing the next group.
- A student who says "wait, that one looks different from the other two" is demonstrating the criterion as clearly as one who reads a scale correctly. Write it down.
Method notes
- Tear pads into thirds. One pad makes three replicates. Two packs cover a class comfortably.
- Vinegar soak is 2 minutes, then squeeze out hard. Soaking longer does not help; leaving it dripping wet slows the reaction because the air cannot reach the metal.
- Treatments go on after the soak — that is the whole point of testing a protective coating.
- Same size pieces. A group that does not control this has an obvious flaw to write about, which is fine, but most will want to fix it once asked.
- Readings at 0, 10, 20 and 30 minutes. Use the same 0–4 coverage scale they have used for five weeks.
- Photograph at every reading. Photos are the backup if a rating turns out to be inconsistent.
What you should see
| Treatment | Expected over 30 minutes |
|---|---|
| Bare control | Obvious orange within 20 min. Warm to the touch. |
| Petroleum jelly | Strong protection where coverage is complete. |
| Paint or nail polish | Good, but hard to coat wool evenly — patchy results are honest results. |
| Oil | Moderate. Thin and it migrates. |
| Tape or plastic wrap | Often worse than expected. Traps moisture against the metal. |
The patchy-coating result is the most useful thing that can happen. It is exactly what the client needs to hear: a coating only protects while it is complete.
What comes next
Week 7 is the write-up and the defence. Students take a final reading at the start of that lesson, so the pads must be stored somewhere safe and undisturbed. They will need their data, their graphs from Week 5, and the other class's dataset.
What you will hear during the swap
| What they say | When | What settles it |
|---|---|---|
| A different result means someone failed | During the swap | Different methods lose and gain in different places. Ask what they did differently before assuming error. |
| Our data is fine, theirs is flawed | Very common in the swap | Turn it around — what would the other class say about ours? Name two things they could legitimately attack. |
Overview
You wrote the plan. Today you run it — and this time nobody is telling you what to do next.
What we are doing today
Rust needs two things: water and air. Your nails proved that, but they took five weeks to do it.
Steel wool rusts much faster. It is made of thousands of thin threads, so there is far more metal touching the air than on a nail. What takes a nail five weeks takes steel wool about half an hour.
You have three pieces. Two get the treatment you chose. One stays bare, so you have something to compare against. Everything else about the three has to be the same, or you will not know whether it was your treatment that made the difference.
You watch them for half an hour and write down what changes. By the end you will know whether your treatment slowed the rust down. Next week you tell the client.
Shape of the lesson
| Phase | Time | What happens |
|---|---|---|
| Sign-off | 10 min | Each group states its hazards and controls aloud. No equipment until then. |
| Set up | 20 min | Steel wool soaked, treated, and started. First reading taken. |
| Run and record | 40 min | Readings at 10, 20 and 30 minutes. Photograph every time. |
| The swap | in the gaps | The other class's graphs from last week, with no method attached. Done between readings, while the jars sit. |
| Plan the report | 10 min | What have we got, what is still missing, who is doing what. |
| Secure | 10 min | Label, store for the week, clear the bench. |
If you are teaching this cold
The whole lesson in order. Each step has its own tab above with the detail.
| Step | You do | Students do |
|---|---|---|
| 1. Sign-off 10 min |
No group touches equipment until it has said its hazards and controls out loud. Approve plans on the spot. | State what could go wrong in their method and what they will do about it. |
| 2. Set up 20 min |
Hand out steel wool, vinegar and jars. Watch that pieces are squeezed out properly — dripping wet wool does not rust. | Three equal pieces of steel wool, two minutes in vinegar, squeezed out hard, treatment on two of them, one left bare. Into labelled jars, first reading taken. |
| 3. Run and record 40 min |
Call the readings at 10, 20 and 30 minutes. Circulate with the observation grid — this is where the Finding criterion is judged. Run the thermometer jar at the front. | Rate all three jars at every reading and photograph them. Write anything odd down while it is still happening. |
| 4. The swap in the gaps |
Hand out the other class’s graphs from last week with no method attached. Written critique before any talking. Stop them the moment a reading is due. | Find two things they cannot tell from the other class’s graphs, one thing that may have gone wrong, and one question. Then turn it around on their own method. |
| 5. Plan the report 10 min |
Keep it short and practical. Who is bringing what next week. | Agree their recommendation so far, their strongest evidence, and the weakest part of their method. |
| 6. Secure 10 min |
Jars stored undisturbed for a week. Collect the data sheets — they do not go home. | Label and store their jars, hand in their record. |
Everything you need
Prepare before the lesson
- Print the observation grid, one page per group, names filled in
- Read every group's approved CP2 plan and pull the equipment they asked for
- Tear steel wool pads into thirds — three per group plus spares
- Decant vinegar into bench containers
- Set up the central temperature demonstration jar
- Clear labelled shelf space for a week of storage
- Print the investigation record sheets
Per group of four
- Steel wool grade 0000 — three equal pieces
- Three jars or clear cups, labelled
- White vinegar for the soak — about 100 mL
- Their chosen treatment materials
- Scales, if their plan uses them
- Tray, paper towel, safety glasses
- Camera or tablet for photographs
Treatments available
- Petroleum jelly
- Clear nail polish
- Candle wax, rubbed on
- Cooking oil
- Electrical tape, plastic wrap
- Nothing — the control
Teacher bench
- Observation grid on a clipboard
- One jar, one steel wool piece, one thermometer — the temperature demonstration
- Board space to log the temperature
- Laminated 0–4 coverage scale
- Spare steel wool and jars
- Spill kit, broken-glass bin
Printed sheets
- Investigation record — one per student
- Group role cards — support tier
- Teacher observation grid — one per group
- Their own CP2 plans, returned
Not needed today
- Nails — steel wool replaces them for speed
- Frypan, kettle, basins, funnels
- The 0.01 g scales, unless a group's plan needs them
What we are learning
Learning intention
We are learning to carry out a repeatable investigation and record data precisely enough to be trusted.
I will be successful when I can…
- follow my own plan, and adjust it when something does not work
- measure and record with the precision the equipment allows
- keep a record another person could check
- find a weakness in a method I did not carry out myself, and in my own
- work so that my results are repeatable
Stretch
- I can run a second trial with one deliberate change, to test whether my first result holds.
- I can spot an odd result while it is happening and write down why I think it happened.
- I can name two things the other class could fairly criticise about our method.
AC9S6I03 — use equipment to observe, measure and record data with reasonable precision.
AC9S6I04 — construct and use appropriate representations to organise and process data.
Your goal for today
Sign-off 10 min
No group gets equipment until it has done this.
Before you are given anything, your group says out loud: what could cause harm in your method, and what you are doing about each one. Not the class rules. Yours.
What counts
| Not good enough | Good enough |
|---|---|
| "We'll be careful." | "Steel wool has sharp fibres, so we're handling it with tongs and washing hands after." |
| "Wear safety glasses." | "We're pouring vinegar, so glasses on and we pour over the tray, not the bench." |
| "Don't break the glass." | "We check our jars for chips first, and carry one at a time with two hands." |
Then check your plan is ready
- Do you have everything on your equipment list?
- Does everyone know which step they are doing?
- Is your recording sheet ready before you start, not after?
Set up 20 min
Move fast and treat all three pieces the same. The only difference between them should be the thing you are testing.
Three equal pieces of steel wool. Soak all three in vinegar for two minutes.
Then squeeze each one out hard. Dripping wet is wrong — the air has to get at the metal.
Apply your treatment after the soak, not before.
Keep one piece bare as your control. Same amount of treatment on every treated piece.
Each piece into its own labelled jar. Label with group, treatment and time started.
Take your first reading now — before anything has changed. That is your zero.
Before you sit back
- Are your three pieces the same size? Does it matter?
- Is anything different between your three jars apart from the treatment?
- What is your zero reading?
Why question 1 matters
A bigger piece has more surface, so it rusts faster — nothing to do with your treatment. If your pieces are noticeably different sizes, that is a real problem with your method. You can fix it now, or you can write about it honestly later. Both are acceptable. Pretending it did not happen is not.
Run and record 40 min
Readings at 10, 20 and 30 minutes. Photograph every time. Between readings you work on the swap — the other class's graphs are on the next tab.
Rate each jar 0 to 4 against the scale you have been using for five weeks.
Rate all three separately. Do not average them in your head. If they disagree, that is data.
Every reading
- Look at all three jars.
- Rate each one, separately.
- Photograph from the same angle each time.
- Write anything odd in the notes column now, not later.
Watch the front bench
One jar at the front has a thermometer in it and one piece of untreated steel wool. The temperature goes on the board as it changes.
- What is happening to the temperature?
- Nothing was heated. So where is the warmth coming from?
- Which of our evidence criteria does this match?
Show the answers
1. It rises, usually by 5 to 10 °C over about fifteen minutes.
2. From the rusting itself. When iron and oxygen join, energy is released — the reaction makes its own heat.
3. "It got hot" — from the list you built in Lesson 1. Back then it was something you noticed. Now it is a number on the board, which is a much stronger piece of evidence.
If something goes wrong
Write down what happened, when, and what you did about it. A method that failed and was honestly described is worth more marks than a tidy result you cannot explain.
- Use your role card — everyone has a job.
- Use the table with the reading times already filled in.
- All four readings, all three jars, photographed.
- Notes written as things happen.
- Set up a fourth jar with one deliberate change and see whether your result still holds.
- Predict where each jar will be by next week, and write it down now.
The swap in the gaps, 20 min
Here are the other class's graphs from last week. You were not there. You do not know how they did it.
They tested something you did not. You tested something they did not. Neither class can answer the client's question alone. But before you use their numbers, you have to decide whether you trust them.
Write these down before you discuss anything
- Two things you cannot tell from this data. What did they not write down that you would need to know?
- One thing you think may have gone wrong. Be specific — name the step.
- One question you would ask them if they were standing here.
Things worth looking for
- Did they dry the nails the same way you did? Would you know if they had not?
- Did every jar start on the same day?
- Were the jars all in the same place — same light, same temperature?
- Did they use the same size nails?
- Is one of their three jars wildly different from the other two? Did they say why?
- Did they record to two decimal places, or round?
- Is anything missing — a week's reading, a jar, a mass?
Now turn it around
What would the other class say about ours? Name two things they could fairly attack about our method.
The turn-it-around question is the harder half and the more important one. A student who can name a weakness in their own method is doing what the evaluation criterion actually asks. Expect resistance; most groups will defend their own data instinctively.
Why this matters
- Could either class have answered the client's question alone?
- Real scientists do this to each other constantly. Why would that make science better rather than worse?
Where this is going
No. One class found out what makes rust happen. The other found out what slows it down. The client needs both, and neither class had the time or the jars to do it all.
Scientists publish their methods precisely so other people can attack them. A finding that survives other people trying to pull it apart is worth far more than one nobody checked. That is not scientists being difficult with each other — it is the part that makes the answer trustworthy.
Plan the report 15 min
Next week you write to [CLIENT NAME]. Work out now what you are missing.
What you will need
- Today's data, all four readings
- Next week's final reading — taken at the start of the lesson
- Your graph from Week 5
- The other class's data
- Your photographs
Work it out as a group
- Based on what you have seen so far, what are you going to recommend?
- What is the strongest piece of evidence you have for that?
- What is the weakest part of your method — the bit they could fairly attack?
- What do you still need before you can write it?
Agree who is doing what
You each write your own report, but the group shares the data and does the defence together. Decide now who is bringing what next week, and who is answering which challenge question.
Secure 10 min
Storing for the week
- Check every jar is labelled: group, treatment, date.
- Lids on the jars that had lids on today. Leave open the ones that were open.
- Onto the shelf, together, out of the walkway.
- Photograph the shelf so you know what it looked like when you left it.
Clearing up
- Vinegar down the sink with the tap running.
- Steel wool into the bin, not the sink — it blocks drains and it rusts.
- Benches wiped, trays stacked, glasses back.
- Wash hands.
Before you go
Hand in your data sheet. You get it back next week. If it is in your bag, it will not be there when you need it.
Next week
Final reading first thing, then the report. You will present to the group and be asked hard questions about how you know what you claim to know.
Resources
Print before the lesson.
PDF All student sheets Investigation record and role cards in one file.