GCSE Physics (AQA)

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Newton's Second Law

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Forces Forces and motion

Newton's Second Law

6:45 Newton's Three Laws
Spec 4.5.6.2.2
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  • Newton's second law states that the acceleration of an object is proportional to the resultant force acting on it and inversely proportional to its mass.
  • This law is crucial for understanding how motion changes when forces are applied.
  • Proportionality means if one quantity doubles, the other also doubles; inversely proportional means if one doubles, the other halves.
  • Example given: a cyclist with forward driving force and backward frictional force; resultant force is the vector sum of these forces.
  • If resultant force increases (e.g., stronger driving force), acceleration increases proportionally.
  • Direction of resultant force and acceleration are important; if aligned with motion, speed increases; if opposite, speed decreases.
  • Example of skydiver: downward weight and upward drag, with resultant force determining acceleration and speed changes.
  • If resultant force is perpendicular to motion, the object changes direction but not necessarily speed.
  • Mass affects acceleration; heavier objects need more force to achieve the same acceleration as lighter objects.
  • Newton's first law is a special case of the second law where the resultant force is zero, leading to no acceleration and constant velocity.
  • Understanding these principles is essential for explaining motion and forces in various contexts, crucial for exams.

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