Newton's Laws

• Newton's laws of motion


  Fundamental principles that describe the relationship between an object and the forces acting upon it
• Newton's three laws of motion

  • Law of inertia
  • Law of acceleration
  • Law of action and reaction
• Law of inertia (Newton's first law)


  • An object at rest will remain at rest, and an object in motion will continue moving at a constant velocity, unless acted upon by an unbalanced force
  • Describes the concept of inertia - an object's resistance to changes in its state of motion
• Applying the law of inertia to a sporting example

  1. Performer is still on the starting block

  2. Performer applies force to overcome inertia and start moving

  3. Performer continues moving until another force is applied
• Law of acceleration (Newton's second law)


  • The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass
  • Described by the equation: Force = Mass x Acceleration
• Mass remains constant during most sporting events
• Ground reaction force

  The force exerted by the ground on an object in contact with it will be equal in magnitude and opposite in direction to the force the object exerts on the ground
• Smaller athletes can generate high acceleration with lower forces due to their lower mass
• Law of action and reaction (Newton's third law)


  • For every action, there is an equal and opposite reaction
  • The forces between two interacting objects are equal in magnitude and opposite in direction
• Applying the law of action and reaction to a sporting example

  1. Athlete applies force to the ground/object

  2. Ground/object applies an equal and opposite force back on the athlete