Forces — Investigation · Physical Science: Matter, Forces & Energy, Grade 8
Model balanced forces, gravity, friction, electric and magnetic interactions, and fluid pressure.
How does magnet distance affect attraction?
Investigate
Does the effect of a magnet on an iron clip change with separation?
Use three sessions: plan the question, boundary and predicted mechanism; collect safe records or analyze the supplied data; then graph, explain, compare with the initial model and propose a revision. The data option needs no special equipment. Time is a suggested allocation, not a measured completion claim.
Materials
- One classroom bar magnet, one iron paper clip
- Ruler, paper surface, tape
- Notebook; provided data can replace the hands-on test
Before you begin
Use a large classroom magnet, not small powerful magnets. Keep magnets away from young children, electronics, and medical devices. Never place magnets or clips in the mouth.
Plan a controlled comparison
Change separation only. Keep magnet, clip, orientation, surface, and resetting procedure the same.
Method
- Make a notice-and-wonder record. State one observation, one possible explanation and a question the investigation can address. Agree on the measuring rule before seeing the results.
- Predict whether separation affects attraction. Draw the initial arrangement.
- Place the clip at a marked position. Keep magnet orientation and the surface fixed.
- At each separation, approach from outside the test area without touching the clip. Record whether the clip moves. Reset and repeat three times.
- Summarize the repeated trials rather than reporting only the trial that fits your prediction.
- Use a field model to explain the pattern and name another variable worth investigating.
- Revise the initial model, label the specific evidence that changed it and state a remaining question. Propose a changed condition, a predicted result and evidence that would challenge your mechanism.
Example data — for analysis when materials are unavailable
Illustrative example data for analysis, not measurements collected by the learner.
| Separation (cm) | Trials where clip moved (out of 3) |
|---|---|
| 1 | 3 |
| 2 | 3 |
| 3 | 2 |
| 4 | 0 |
Analyze and explain
- What relationship is supported?
- Why do these data not prove an exact force law?
- What could cause mixed results at 3 cm?
- Explain why a movement/no-movement outcome is not a direct force reading. Propose a method that could measure force more directly while controlling separation.
What a strong explanation includes
- Cite results at two separations.
- Identify the changed and controlled variables.
- Separate an observed pattern from a stronger claim the measurements cannot support.
- Identify the system, relevant variables and measurement method.
- Explain a model revision and a specific uncertainty.
Parent / teacher guide: discuss after the investigation
In the illustrative results, movement occurred in all trials at 1 and 2 cm but none at 4 cm. This supports a stronger interaction at closer separation in this setup. The test records movement, not force directly; friction and slight placement differences may explain variation at 3 cm. Explain why a movement/no-movement outcome is not a direct force reading. Propose a method that could measure force more directly while controlling separation. A complete report separates observation from inference. Preserve all planned trials, including a result that does not fit the prediction, and distinguish missing readings from zeros. The supplied numbers are illustrative, not records the learner collected. If observations differ, check the method, units and conditions before deciding which claim is supported. A schematic model should connect parts through a mechanism and explicitly name its limits. Describe a follow-up that changes one intended condition, keeps influential others comparable, and states the possible result that would challenge the explanation. A proposed improvement is not confirmed until it is retested. Different defensible conclusions can receive credit when they use the actual evidence and meet the stated criteria.
Compare this model with the learner’s actual evidence. Different measurements can support a different conclusion; check the reasoning and limitations, not matching wording.