Force Addition

• The normal force is perpendicular to the surface that an object contacts
• The size of the normal force is equal to the weight of the object but in the opposite direction when the object is not moving
• The ground reaction force is equal in magnitude and opposite in direction to the force that the body exerts on the supporting surface through the foot
• The net force acting on an object is the sum of all the external forces acting on it
• Forces that have the same line of action:

  • 500 N
  • 200 N
  • 700 N
  • 500 N
  • 200 N
  • 200 N
  • 500 N
  • A larger force minus a smaller force. Take the direction from the larger force
• The vertical ground reaction force (normal contact force) acting under a runner's foot is 2000 N, while the frictional force is 600 N acting forward
• The peak vertical reaction force is 1200 N acting upward on Daisy, while the braking frictional force is 200 N acting backward on Daisy
• Brian, a 200 kg strongman competitor, is in a state of static equilibrium. He exerts a force of 2200 N at an angle of 14° above horizontal on the cable and a horizontal force of 650 N on the rope. The external forces acting on Brian are:

  • Weight = 1962 N downward
  • Pulling force Rope = 650 N to the right
  • Pulling force Cable (Vest) = 2200 N at 14° counterclockwise from horizontal
  • The normal force (R) is equal in magnitude to the sum of all vertical forces but in the opposite direction
• • The friction force (F) is equal in magnitude to the sum of all horizontal forces but in the opposite direction
  • Only the pulling force cable is not purely vertical or horizontal, so it must be broken down into vertical and horizontal components