IB DP Physics lesson pack on static and dynamic friction for Topic A.2 Forces and momentum, SL and HL, first assessment 2025: one chair, one force meter, and the two laws that come out of its readings. Editable worksheet, 35-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 is the part of the contact force acting along the surfaces, and it comes in a pair: one force on each body, which the students draw.
- The coefficient of friction has no unit and is measured for a pair of surfaces, not looked up for a material. Here it comes out of the demonstration’s own two readings.
- Static friction rises to match whatever is pulling, up to a limit and no further, which is why its law is an inequality and the dynamic law an equality.
- The comparison every friction question turns on, and the two cases it selects: the body holds, or it slides and dynamic friction sets its acceleration.
IB skills (Tool 3: Mathematics):
- Draw and interpret free-body diagrams (practised).
- Resolve vectors into two perpendicular components (practised).
- Interpret features of graphs: maxima and changes in gradient (practised).
- Understand direct proportionality between variables (practised).
What’s included:
- Student Worksheet - 14 pages
- Teacher Key - 24 pages
- Worked Solutions - 12 pages
- Assessment - 8 pages
- Lesson deck - 35 slides
Four exam-style questions and five multiple-choice items: 47 marks across 16 parts, and eight figures, five of which the students draw force arrows onto. Question 1 works the chair through four different pulls: at 19 N against a limit of 19.6 N the friction is 19 N and not 19.6 N, which is the case this lesson exists for. Question 2 puts a loose crate on the open bed of a truck pulling away, where the friction on it points forwards.
The slope and the push at an angle are set as exam practice rather than worked in the taught hour. 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:
- Newton’s Second Law: F = ma, the lesson before this one
- Free-Body Diagrams and Force Pairs, where those diagrams are taught
- Upthrust, Viscous Drag and Terminal Velocity, the lesson that comes next
- Resultant Force, Inertia and Newton’s First Law, where zero resultant force is taught
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