This numeracy exercise for schools can be adapted to grades pre-up. You need:
1. A number of strong magnets, at least two per group
2. Iron filings
3. Selection of nuts of various metals: iron, copper, brass, some lead sinkers.
The hour long exercise is presented as an introduction to scientific thinking in the higher grades. I don’t worry about this for lower grades.
I usually choose an assistant to help handing out magnets, though this changes throughout.
1. Discovery – I introduce the magnets as my “floater rays”. I let them explore the repulsion of the magnets, showing how the magnet can “float” above another if in the correct orientation. I also do the moving the magnet under the desk trick.
2. Theory formation/induction – I hand out more magnets suggesting they find out what magnets are attracted too. After exploring for a while I solicit the theory, invariably “metal”. I ask them to put up their hand if they agree this is a good theory or not. (All usually agree with the theory).
3. Falsification/tests – I hand out nuts of various metals, indicating that we are going to test this theory. They soon get the point that their theory is wrong, and I cross it out on the board.
4. Refinement – Together we refine the theory that only certain metals are attracted, etc.
5. Visualization/schematics – I place a bar magnet (or the group of 8 or so magnets) under a piece of paper and sprinkle iron filings on top, Awesome! and Cool! are the usual responses at this stage. I introduce it by asking “Would you like to see my floater rays?”.
I get them to draw the rays on a piece of paper, but then go around an draw the schematic lines of magnetic force (familiar magnetic field for a bar magnet). I explain the difference between an artistâ€™s impression, and a schematic diagram.
6. Measurement/Numeracy – For prep and lower classes, I will get them to number the field lines in their schematic. For higher grades I go into the measurement phase, asking them to design an apparatus for measuring the strength of one or two magnets.
The way I do it is to attach one of the iron nuts to three or so rubber bands, and measure the extension as a magnet is pulls the nut against the band. This can be done next to a ruler, so is very easy to set up. I am sure there are other ways.
As I collect the (3) lengths from the groups, I list them in a table, calculate the differences (to get the extension) then add the numbers up. This is an opportunity to test their mental arithmetic and encourage agility.
The strength of one, two, three magnets etc. can be indicated from the overall result. More elaborate approaches are possible with higher level classes.