Newton's Second Law Of Motion - Forces, Motion And Energy - BBC

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In this guide

  1. Revise
  2. Test
  1. Forces, motion and energy
  2. Friction
  3. Balanced and unbalanced forces
  4. Newton's laws
  5. Weight, mass and gravity
  6. Newton's Second Law of motion

Newton's Second Law of motion

Newton's Second Law of Motion is concerned with the effect that unbalanced forces have on motion.

An unbalanced force acting on an object causes it to accelerate. There are two points to note about the acceleration of an object when an unbalanced force acts on it.

  • The bigger the unbalanced force acting on the object the bigger the acceleration of the object.
  • The more mass the object has, the more inclined it is to resist any change to its motion. For example, if you apply the same unbalanced force to a mass of \(1000 kg\) and a mass of \(1 kg\), the acceleration (change in motion) of the \(1000 kg\) mass will be much less than that of the \(1 kg\) mass.

Newton's second law provides a relationship between the unbalanced force on the object, the mass of the object and the acceleration that is produced. The amazing thing is that the relationship can be expressed neatly by a straightforward mathematical equation.

\(unbalanced\,force = mass \times acceleration\)

\(F = ma\)

The unbalanced force \(F\) is measured in Newtons \((N)\), the mass \(m\) is measured in kilograms \((kg)\) and acceleration a is measured in metres per second per second \(m\,s^{-2}\).

Learn how forces make things move.

Forces, mass and acceleration

Newton's Second Law

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More guides on this topic

  • Revise: Speed and acceleration
  • Video: Acceleration

Related links

  • BBC Science
  • BBC News: Science
  • BBC Lab UK
  • SQA National 4 Physics
  • Physics.org
  • The Physics Classroom
  • Physics Central

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