Free fall: test a plausible explanation
Invite learners to examine the evidence for a falling-object claim, then revise it with its conditions made explicit.
Use this example in the lesson guide ↗Learning objective
Explain why objects have the same gravitational acceleration in an ideal model without air resistance, and distinguish that model from an actual fall.
Prior knowledge
Speed, acceleration, gravitational force and reading a time graph.
Teacher preparation
In Personal teacher notes, record the initial misconception you want to test. Prepare one matched pair of motion records and label each as measured, modelled or illustrative. Preview Projectile Motion with and without drag; use matched launch conditions and explain that a vertical launch is motion under gravity, rather than a measurement of an object dropped from rest.
Possible teaching sequence
- Multiple-choice question bank ↗
Elicit a prediction
7 minTeacher: Ask: ‘If two objects differ in mass, what would you expect to change during their fall, and why?’ Collect reasons before displaying answers.
Learners: Answer a selected mechanics question individually, then compare explanations in pairs.
Check for understanding: Distinguish ‘heavier falls faster’ from a conditional claim about air resistance.
- Projectile Motion ↗
Explore the ideal model
13 minTeacher: Use matched vertical-launch conditions in Projectile Motion. Change mass while drag is off, then contrast with a drag-on run. Ask which assumptions are being changed.
Learners: Record settings and compare the modelled trajectories; keep model outcomes separate from actual measurements.
Check for understanding: Learners identify the no-drag assumption and do not treat the model as experimental proof.
- Math & science dictionary ↗
Interpret evidence
12 minTeacher: Provide the prepared motion records. Ask learners to compare velocity changes over equal intervals and to name units.
Learners: Annotate the records and calculate or describe acceleration where the data permit it.
Check for understanding: Look for rate-of-change reasoning, consistent units and appropriate limits on the conclusion.
- AI problem generator ↗
Build and revise a claim
12 minTeacher: Use a reviewed open-response task asking whether a claim is supported by the stated evidence. Give a prompt about assumptions before giving a worked solution.
Learners: Write a claim, supporting evidence and reasoning, then revise after peer questioning.
Check for understanding: The explanation separates gravitational acceleration from drag effects; mass alone is not used as the whole explanation.
- AI quiz generator ↗
Check transfer
6 minTeacher: Ask the exit question below without the model on screen. Use a short prepared quiz only after collecting independent reasoning.
Learners: Explain a new case individually and identify one limitation of the evidence.
Check for understanding: Use explanations, rather than the quiz score alone, to decide what needs reteaching.
Ready-to-use exit task & teacher answer
Independent task
Two compact objects fall in an ideal vacuum model near Earth. One has twice the mass. Compare their gravitational force and acceleration.
Teacher answer guidance
The heavier object's gravitational force is twice as large, but its acceleration is the same: a = F/m = g. This conclusion assumes the stated ideal conditions.
Where AI might help
Ask the problem generator for one comparison of ideal and drag-affected falling motion. Ask the quiz generator for three questions about acceleration and assumptions. Check every answer against the chosen model and course reference before class.
Keep under educator control
Choose evidence with an explicit source, inspect axes and units, and keep air resistance and launch conditions visible. Follow local procedures if using physical apparatus. Do not claim a classroom drop establishes an exact universal result.
Support and extension
Support: Provide a partially labelled graph and a frame: ‘Under ___ conditions, the evidence supports ___ because ___.’
Extend: Compare predicted drag effects for equal masses with different areas, explaining why a simple mass-only rule fails.
Without AI
Use a printed, clearly labelled model table and teacher-selected motion records with the same prediction, comparison and transfer questions.
Design lens: Inquiry-based learning.