IB DP Physics (2025) A3.5 Mechanical Energy and Friction

IB DP Physics mechanical energy and friction lesson pack, Topic A.3 Work, energy and power, SL and HL, first assessment 2025: non-conservative forces, and how the work done by friction, air resistance or a push from outside changes the mechanical energy. Editable worksheet, 64-slide lesson deck, teacher key, worked solutions and a questions-only assessment, supplied as self-contained HTML plus colour and black-and-white PDF.

What students learn

• Friction changes the mechanical energy of a sliding body by exactly the work it does, and so does a push or pull from outside.
• Where the energy goes: thermal energy of the body and its surroundings, transferred, not destroyed.
• Why a weight is a conservative force, and friction and air resistance are not, from the work each does over a round trip.
• Problems in stages, carrying the energy at the end of one stage into the next as the forces doing work change.

IB skills (Tool 3: Mathematics, with Inquiry 3):

• Use approximation and estimation (practised).
• Appreciate when an effect can be neglected (practised).
• Derive relationships algebraically (practised).
• Propagate uncertainties in processed data (practised).
• Discuss the impact of uncertainties on a conclusion (practised).
• Evaluate the weaknesses and assumptions of a method (practised).

What’s included:

• Student Worksheet - 19 pages
• Teacher Key - 33 pages
• Worked Solutions - 23 pages
• Assessment - 15 pages
• Lesson deck - 64 slides

Nine structured questions and four multiple-choice items: 66 marks across 43 parts, and fourteen figures. Your class works five questions, 35 marks, in the lesson, between two opening votes and a multiple-choice exit ticket. Everything else goes home, including three exam-style questions and a ten-mark data question in the Paper 1B pattern: a block pulled along a bench by a falling hanger, with friction and its uncertainty found from one measured speed.

Every resistive force is constant or found from its work: no area under a force-distance graph. Power and efficiency come in later lessons. Worksheet and deck open in any modern browser with nothing to install, and the worksheet is fully editable. SI units, IB notation and IB command terms throughout. Suitable for grades 11-12 (ages 16-19) as a lesson, cover lesson, homework or revision.

Related resources:

• Conservation of Mechanical Energy I, the frictionless lesson before this one
• Concluding and Evaluating, the skill pack behind the data question
• Fluid Resistance, where neglecting air resistance is taught
• Scientific Notation, SI Prefixes and Estimation, the skill pack behind the estimates (free)

Updated 1 Nov 2026: please reprint.
A rating helps other teachers find this.