2.2 Newton's Laws

• Inertia

  • Inertial forces are those that resist any change to the velocity or state of motion of an object.
  • The inertia of an object depends on its mass. The greater the mass, the greater the inertia.
  • This means a greater force is required to change the motion of a heavier object, as inertia has to be overcome.
• Newton's First Law

  • "A body will travel with uniform motion along a straight line or remain at rest unless acted upon by a resultant force"
  • This means that if forces are balanced, the motion of an object will remain unaffected since their is no resultant force
  • An object remaining still, continuing at a constant velocity, or floating in still water would all be examples of balanced forces

  
• Newton's Second Law

  • "A resultant force acting on a body will cause a change to its velocity"
  • The resultant force causes an acceleration of the object, the magnitude of which depends on the object's mass
  • Force (N) = Mass (kg) x Acceleration (m/s²)

  
• Newton's Third Law

  • "When two objects interact, they exert equal and opposite forces on each other"
  • For example, if a person jumps from a boat, the person will move forward (the action) and the boat will move backwards (the reaction)

  
• Terminal speed

  As an object starts to move through a fluid such as air or water, resistance (drag) forces increases, opposing the motion of the object. Eventually these drag forces will be equal to the driving force so the object moves at a constant speed. There is no longer a resultant force acting, so the object continues to move at a constant speed, known as its terminal velocity