Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
Recall and use Newton’s second law as: force (newton, N) = mass (kilogram,…
Full specification wording
Topic 2 – Motion and forces: 2.15 Recall and use Newton’s second law as: force (newton, N) = mass (kilogram, kg) × acceleration (metre per second squared, m/s²)
Newton's second law links the resultant force on an object to how quickly its velocity changes.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 15 of 32
Study notes
From the checked teaching notes for this specification point.
The idea
Newton's second law links the resultant force on an object to how quickly its velocity changes. The equation is F = m × a, where force F is in newtons (N), mass m in kilograms (kg) and acceleration a in metres per second squared (m/s²). One newton is the resultant force that gives a 1 kg mass an acceleration of 1 m/s². To use it, find the resultant force first, then divide by mass to get acceleration, or multiply mass by acceleration to get force. Example: a resultant force of 12 N on a 3 kg trolley gives a = F ÷ m = 12 N ÷ 3 kg = 4 m/s². Always convert grams to kilograms and keep units consistent before substituting.
What earns the marks
- States the equation as force = mass × acceleration and identifies the unit of force as the newton (N).
- Rearranges the equation correctly to give acceleration = force ÷ mass or mass = force ÷ acceleration.
- Substitutes values with mass in kilograms and acceleration in m/s² to obtain a force in newtons.
- Explains that the force in the equation is the resultant force acting on the object.
Common mistakes and how to put them right
Multiplies mass by acceleration when asked for acceleration.
Put it right: Divide force by mass instead.
Uses mass in grams in the equation.
Put it right: Convert to kilograms first so the force comes out in newtons.
Treats any single applied force as the resultant force.
Put it right: Add or subtract forces to find the resultant before substituting.
Exam tips
- Write the equation, then rearrange it before substituting numbers so the working is clear.
- Check units: mass in kg and acceleration in m/s² give force in N.
- Show the substitution line, for example F = 3 kg × 4 m/s² = 12 N, to secure method credit.
Try the lesson
The start of the Topic 2 – Motion and forces: 2.15 Recall and use Newton’s second law as: force (newton, N) = mass (kilogram, kg) × acceleration (metre per second squared, m/s²) lesson, made from checked teaching notes for this specification point.
Have a go first
A cyclist and bicycle have a combined mass of 80 kg and accelerate at 0.5 m/s². What resultant force acts on them?
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