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Downhill without a motor: where does the energy go?

Grade VII pupils use PLA to draw a sled slider and two cross supports (60mm, 90mm), each with a foot. They use a ruler as a slope, release the slider twice from each height and mark the stopping positions on T2. They describe the change from gravitational potential energy to kinetic energy and losses due to resistance to motion. Optional: repeat on paper.

Age
12–14 years
Length
approx. 45 min
Level
Medium
Where you teach
School
Purpose
Educational
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How to run this session

Stages and timing
  1. Sled: slider with a flat underside
  2. Sliding test: when will the sled move?
  3. Low support: 60 mm wall
  4. Low support: foot
  5. High support: 90 mm wall and foot
  6. Setup: ruler on a support
  7. Descent from low support
  8. Descent from high support and comparison
  9. Where does the energy go?
  10. Extension: another surface

What gets built

A slider, two supports and a run-out sheet with four stop marks (two from the low support, two from the high support), plus an observation sheet comparing “further / nearer” and describing energy changes.

What it practises
  • Qualitatively compare trials from two heights and explain that greater height means greater initial gravitational potential energy; actual run-out also depends on resistance.
  • Identify resistance to motion (friction) as the cause of stopping and the conversion of mechanical energy into internal energy (warming).
  • Plan a fair comparison: the same ruler, table surface and start mark; change the height and repeat twice to check consistency.
  • Understand the model’s limits: run-out distance does not measure energy; mechanical energy can dissipate through deformation and sound at the transition to the table.

Success criteria
  • The pupil compares actual stopping marks from two heights, identifies agreement or variation between trials and explains the conversion of gravitational potential energy into kinetic energy and energy dissipation due to resistance; run-out is not a direct measurement of energy.
  • Observation sheet: prediction, two circles from the low support, two crosses from the high support, three energy-change fields (start, bottom of ruler, finish).
  • The support stands without tipping; the longer foot section points away from the ruler zero; the cross-support slots remain open.

What you need
Filament
PLA
Colours
colour shown in the illustration
Also
3D pen (one per pupil), PLA filament (one colour per pupil, unchanged during the lesson), transparent work mat, pen stand, T1: 1:1 PLA part patterns (supplied printout), T2: run-out sheet (supplied printout), observation sheet (supplied printout), smooth, straight plastic ruler, 20 or 30 cm, with graduations (pupil equipment), adhesive tape, pencil, A4 paper (optional extension)

Files

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Version 1a8af226-f324-4c32-8b45-197c184cfd30 Updated 2026-10-14

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