Newton's Laws

• Newton's First Law:

  According to Newton's First Law of motion, an object remains in the same state of motion unless a resultant force acts on it. If the resultant force on an object is zero, this means:

  • a stationary object stays stationary
  • a moving object continues to move at the same velocity (at the same speed and in the same direction)

  Inertia - The tendancy of an object to continue in its current state (at rest or in uniform motion) is called inertia.
• Newton's Second Law:

  resultant force = mass x acceleration

  F = m a

  This is when:

  • force (F) is measured in Newtons (N)
  • mass (m) is measured in kilograms (kg)
  • acceleration is measured in metres per second squared (m/s²).

  The equation shows that the acceleration of an object is:

  • proportional to the resultant force on the object
  • inversely proportional to the mass of the object

  In other words, the acceleration of an object increases if the resultant force on it increases, and decreases if the mass of the object increases.
• Newton's Third Law:

  According to Newton's Third Law of Motion, whenever two objects interact, they exert equal and opposite forces on each other.

  This is often worded as 'every action has an equal and opposite reaction'. However, it is important to remember that the forces act on two different objects at the same time.