IB DP Physics (2025) A2.4 Newton's Second Law F = ma

IB DP Physics lesson pack on Newton’s second law and F = ma for Topic A.2 Forces and momentum, SL and HL, first assessment 2025: how a resultant force sets the acceleration of a body, and how the three laws work as one system. Editable worksheet, 42-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

• Newton’s second law, F = ma, rearranged for each of its three unknowns and chained to the equations of motion.
• The acceleration follows the resultant force, never the velocity: a braking lorry accelerates backwards.
• The two proportionalities: directly with the resultant force at constant mass, inversely with the mass at constant force, both sketched as graphs.
• The newton as a derived unit, kg m s⁻², defined so that the law needs no constant of proportionality.
• Which of the three laws answers which question, and the two-move method for bodies that move together: the system, then one body alone.

IB skills (Tool 3: Mathematics):

• Understand direct and inverse proportionality (taught).
• Select and manipulate equations (practised).
• Express derived units in terms of SI units (practised).
• Calculate mean and range (practised).
• Propagate uncertainties in processed data (practised).
• Express quantities and uncertainties to an appropriate number of significant figures (practised).
• Understand the significance of uncertainties in raw and processed data (practised).

What’s included:

• Student Worksheet - 18 pages
• Teacher Key - 27 pages
• Worked Solutions - 14 pages
• Assessment - 10 pages
• Lesson deck - 42 slides

Seven questions and five multiple-choice items: 62 marks across 26 parts, and seven figures, three of which the students sketch a graph or draw force arrows onto. The last is a data question: five balance readings to a mean and its uncertainty, propagated through a product and a difference, then ranked by contribution.

The law is taught and worked here rather than measured in the laboratory, and it is stated for a body of constant mass. 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:

• Resultant Force, Inertia and Newton’s First Law, the lesson before this one
• Free-Body Diagrams and Force Pairs, where the third law is taught
• Uncertainties, the skill pack behind the data question
• Foundations of Motion: Distance and Displacement, a free lesson pack to try first