The shape of the lesson
By the end of the lesson, learners can
- Lift it higher, store more: Set the mass and lift the object to different heights.
- Mass, gravity, height: The defining equation and two useful rearrangements:
- Vertical height only: on a slope, use the rise, not the slope length.
- Units: mass in kg, g about 9.8 N/kg (or 10 if told), energy in J.
- On falling: mgΔh becomes ½mv².
One picture every idea returns to
The change in gravitational potential energy is ΔPE = mgΔh, where m is mass, g is the gravitational field strength (about 9.8 N/kg on Earth) and Δh is the change in height. It is measured in joules.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Energy banked by height.. Lift an object and you store energy in it, ready to be released the moment it falls. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Lift it higher, store more | Set the mass and lift the object to different heights. Project tab 4 of the lab (Gravitational potential energy) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Mass, gravity, height | The defining equation and two useful rearrangements: Model the worked example Worked example on the board, one line at a time. | Round Table |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 13 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Mass, gravity, height, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Round Table
One sheet travels round the team. Each student adds one line of working or one idea and passes it on, so the solution is built four hands at a time and every contribution is visible.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Use the change in height, measured vertically, not the distance travelled along a ramp or slope. | A 10 m slope that rises 3 m vertically gives Δh = 3 m, not 10 m. And use the value of g the question gives you, whether that is 9.8 N/kg or the rounded 10 N/kg. |
Gravitational potential energy (ΔPE = mgΔh): worksheet
6 questions, 13 marks. Written in the style of the papers; no past paper question is reproduced.
Write the equation for the change in gravitational potential energy, and state what each symbol represents.
A 5.0 kg mass is raised vertically by 3.0 m. Using g = 9.8 N/kg, calculate the gain in gravitational potential energy.
A 0.40 kg book is lifted onto a shelf 1.5 m above the floor. Using g = 10 N/kg, calculate the gain in gravitational potential energy.
A box is pushed up a long sloping ramp to a raised platform. Explain which distance must be used to find the gain in gravitational potential energy.
A 2.0 kg mass falls from rest through a height of 5.0 m. Using g = 9.8 N/kg and ignoring air resistance, calculate its speed just before it lands.
Lifting a 4.0 kg load gives it 240 J of gravitational potential energy. Using g = 10 N/kg, calculate the height it was raised.
Answer key and marking notes
- ΔPE = mgΔh. ✓
- m = mass (kg), g = gravitational field strength (N/kg), Δh = change in height (m). ✓
- ΔPE = mgΔh = 5.0 × 9.8 × 3.0
147 J
- ΔPE = 0.40 × 10 × 1.5
6.0 J
- Use the vertical height gained, not the length along the ramp. ✓
- Only the vertical rise changes the gravitational potential energy. ✓
- ΔPE = mgΔh = 2.0 × 9.8 × 5.0 = 98 J
½mv² = 98 → v² = 98 ÷ 1.0 = 98
v = √98
v ≈ 9.9 m/s
- 240 = 4.0 × 10 × h
h = 240 ÷ 40
h = 6.0 m
2 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
A 5.0 kg mass is lifted 3.0 m. Taking g = 9.8 N/kg, what is the gain in gravitational potential energy?
- A15 J
- B49 J
- C147 J
- D1441 J
A pendulum swings from its highest point to its lowest point. Ignoring air resistance, which statement is correct at the lowest point?
- Aall the gravitational potential energy lost has become kinetic energy
- Bthe kinetic energy is zero
- Cthe gravitational potential energy is at its maximum
- Denergy has been destroyed during the swing
Quiz key
ΔGPE = mgΔh = 5.0 × 9.8 × 3.0 = 147 J. Option A ignores g; B forgets the height.
At the lowest point the height is least (so GPE is least) and the speed is greatest (so KE is greatest); the GPE lost equals the KE gained. Options B and C describe the highest point. D breaks conservation of energy.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.