AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Newton's Second Law: resultant force = mass × acceleration
This statement gives the word equation for Newton's Second Law: resultant force = mass × acceleration.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 4 of 13
- 2 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
This statement gives the word equation for Newton's Second Law: resultant force = mass × acceleration. It tells you that the acceleration of an object is directly proportional to the resultant force acting on it and inversely proportional to its mass. For example, if a resultant force of 12 N acts on a 3 kg object, the acceleration is 12 ÷ 3 = 4 m/s². If the same 12 N acts on a 6 kg object, the acceleration is only 2 m/s². The equation is usually written as F = m × a, where F is resultant force in newtons (N), m is mass in kilograms (kg) and a is acceleration in metres per second squared (m/s²). You must be able to use this equation to calculate any one of the three quantities when the other two are known, and to describe how changing force or mass affects acceleration.
What earns the marks
- States the word equation: resultant force = mass × acceleration.
- Identifies F as resultant force in newtons (N), m as mass in kilograms (kg) and a as acceleration in metres per second squared (m/s²).
- Calculates acceleration using a = F ÷ m when resultant force and mass are known.
- Calculates mass using m = F ÷ a when resultant force and acceleration are known.
- Explains that for a constant mass, acceleration is directly proportional to resultant force.
- Explains that for a constant resultant force, acceleration is inversely proportional to mass.
Common mistakes and how to put them right
Confusing the rearrangement and writing a = m ÷ F.
Put it right: A = F ÷ m, because acceleration increases with force and decreases with mass.
Forgetting to find the resultant force when several forces act.
Put it right: Calculate the vector sum of forces first, then substitute into F = m × a.
Mixing units, such as using mass in grams with acceleration in m/s².
Put it right: Convert mass to kilograms before calculating.
Exam tips
- Underline the values given in the question and identify which quantity you need to find.
- Show the rearranged equation before substituting numbers, especially when finding mass or acceleration.
- Give the unit with your final answer; for acceleration use m/s², for force use N and for mass use kg.
Try the lesson
The start of the Newton's Second Law: resultant force = mass × acceleration lesson, made from checked teaching notes for this specification point.
Have a go first
A cyclist and bicycle have a total mass of 80 kg. The cyclist accelerates at 0.5 m/s². Calculate the resultant force acting on the cyclist and bicycle.
Listen
This statement gives the word equation for Newton's Second Law: resultant force = mass × acceleration. It tells you that the acceleration of an object is directly proportional to the resultant force acting on it and inversely proportional to its mass. For example, if a resultant force of 12 N acts on a 3 kg object, the acceleration is 12 ÷ 3 = 4 m/s². If the same 12 N acts on a 6 kg object, the acceleration is only 2 m/s². The equation is usually written as F = m × a, where F is resultant force in newtons (N), m is mass in kilograms (kg) and a is acceleration in metres per second squared (m/s²). You must be able to use this equation to calculate any one of the three quantities when the other two are known, and to describe how changing force or mass affects acceleration. A strong answer earns marks for these points. States the word equation: resultant force = mass × acceleration. Identifies F as resultant force in newtons (N), m as mass in kilograms (kg) and a as acceleration in metres per second squared (m/s²). Calculates acceleration using a = F ÷ m when resultant force and mass are known. Calculates mass using m = F ÷ a when resultant force and acceleration are known. A common slip: Confusing the rearrangement and writing a = m ÷ F. Instead, a = F ÷ m, because acceleration increases with force and decreases with mass. Exam tip: Underline the values given in the question and identify which quantity you need to find.
See it
Key words
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Newton's Second Law
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Force, mass and acceleration calculations
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See every definition
- Newton's Second Law
- The word equation for this is resultant force = mass × acceleration.
- Force, mass and acceleration calculations
- The equation F = m × a can be used to calculate any one of the three quantities when the other two are known.
Label the diagram
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1Box 1
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3Box 3
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