Resultant Force

• What is resultant force?

  The single force representing the sum of all the forces acting on an object
• How can resultant force be found?

  If more than one force act on a straight line, adding (acting in same direction) or subtracting (acting in opposite directions) them
• Skydiver Example?

  • Initially, the skydiver has no air resistance and the only force acting on him is weight
  • As he falls, he accelerates, increasing his speed (A)
  • Resultant is simply 833N down
  • As air resistance increases, the resultant force from weight decreases (B)
  • Resultant is 833 - 350 = 483N down
  • So acceleration decreases, so he is not speeding up as quickly (C)
  •  Resultant is 133N down
  • Eventually they are equal and balance, so there is no resultant force (D)
  • Resultant = 0
  • So there is no acceleration when the resultant force is 0 they travel at terminal velocity.

  
• What do free body diagrams show?

  The forces (and their directions) acting on object, like for the skydiver above