Motion — Investigation · Physical Science: Matter, Forces & Energy, Grade 8
Describe movement with measurements and graphs, then use Newton’s laws to explain changes.
Investigate a model collision protector
Investigate
How can stopping conditions change temporary deformation and measured peak force?
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
- Notebook, ruler and the supplied original illustrative dataset
- Optional lightweight toy cart, folded soft paper padding, tray and adult help
- No force sensor is needed for the data-analysis version
Before you begin
Use the supplied records for force comparisons. Optional observations use only a lightweight toy and soft padding on a low contained surface with adult supervision. Never test on people, animals, real phones, glass or safety equipment; do not drop objects from height. Keep the path clear and stop if a sample breaks.
Plan a controlled comparison
Compare protector arrangements with the same toy mass, starting-speed rule, impact direction, target and force-recording method. Define permanent deformation and peak force before comparing outcomes. Padding geometry changes; do not silently change speed as well.
Method
- Read the chapter launch, list observations and questions, and sketch the toy and padding before, during and after contact.
- State a testable question about one padding feature. Define a criterion, such as reduced peak, and a constraint, such as maximum 5 cm thickness.
- Use the supplied records, or make only safe visual toy observations. Do not invent force readings if no sensor was used; separate visible deformation from instrument values.
- Compare all three trials for each design. Calculate mean peak and range, and check compliance with thickness limits.
- Draw interaction arrows on separate receivers and an energy-path model. Explain how compression may spread stopping over distance and time without erasing energy.
- Propose a changed arrangement within the size limit. Predict its outcome and plan a matched repeated retest, checking permanent deformation as well as peak.
- Write a revised explanation with the evidence that changed the first model and one limit of transfer to real objects.
Example data — for analysis when materials are unavailable
Illustrative example data for analysis, not measurements collected by the learner.
| Design | Thickness (cm) | Peak forces in 3 trials (N) | During/after observation |
|---|---|---|---|
| Rigid model stop | 0 | 24, 25, 23 | No cushion compression |
| Soft arrangement A | 4 | 12, 14, 13 | Compresses; mostly recovers |
| Soft arrangement B | 7 | 8, 10, 9 | Compresses; mostly recovers |
Analyze and explain
- Calculate mean peaks and ranges. Compare all trials rather than only the most favorable reading.
- Which designs satisfy the 5 cm thickness constraint? Explain why a low peak alone does not decide.
- Distinguish equal interaction forces from different accelerations, and explain the roles of contact time, temporary shape change and starting speed.
- Propose a revision within the hard limit and identify a possible result that would challenge its predicted advantage.
What a strong explanation includes
- Use the three-trial means: 24, 13 and 9 N; ranges: 2, 2 and 2 N.
- Apply the 5 cm constraint rather than choose an ineligible design.
- Explain separate receivers for an interaction pair.
- Connect stopping, deformation and an energy pathway.
- State a bounded conclusion and a controlled retest.
Parent / teacher guide: discuss after the investigation
In the illustrative records, the rigid stop averages 24 N, A 13 N and B 9 N; each three-trial range is 2 N. Both padded arrangements show temporary compression and mostly recover afterward. A is a qualifying model protector at 4 cm, while B exceeds the 5 cm limit despite its lower mean peak. These data support a lower measured peak for A than the rigid stop under the matched starting conditions. They do not certify safety for people or real devices. A plausible mechanism is that compressible padding increases the stopping distance and time, often reducing typical and peak forces. Equal interaction forces act on different objects and do not require equal accelerations. Energy can transfer into deformation, thermal changes, sound and surroundings rather than disappear. A useful revision might change A’s padding arrangement while retaining its thickness limit. It needs new matched tests and damage observations; its performance cannot be assumed from combining features. If actual toy observations are used without a force sensor, record shape and motion evidence only, and identify instrument values as supplied illustrative data.
Compare this model with the learner’s actual evidence. Different measurements can support a different conclusion; check the reasoning and limitations, not matching wording.