Newton’s First Law (HL IB Physics)

• Newton's laws of motion describe the relationship between the forces acting on objects and the motion of the objects

• Newton's first law of motion states:

A body will remain at rest or move with constant velocity unless acted on by a resultant force

• This means that:
  • An object at rest will remain at rest unless acted upon by a resultant force
  • An object moving with a constant velocity will remain moving at that constant velocity unless acted upon by a resultant force

• A resultant force is required to change the motion of an object
  • To speed up
  • To slow down
  • To change direction

• If the resultant force acting on an object is zero, it is said to be in translational equilibrium
• If the resultant force is zero (the forces on a body are balanced), the body must be either:
  • At rest
  • Moving at a constant velocity

  

For both cases of the football being at rest or moving at a constant velocity, its resultant force is 0

• Since force is a vector, it is easier to split the forces into horizontal and vertical components
• If the forces are balanced: 
  • The forces acting to the left = the forces acting to the right
  • The forces acting upward = the forces acting downward

• The resultant force is the vector sum of all the forces acting on the body