C1 Force and Motion II

• Force (N) is vector quantity that has magnitude and direction.
• Resultant force is the vector sum of two or more forces acting on an object.
• When resultant force is zero AKA forces in equilibrium, forces on both directions are equal.
• Hot-air balloon:

  • move forward : forward force > friction
  • move up : upward force > weight
  • move down : weight > upward force
• Fx = F cos θ

  Fy = F sin θ = F cos (90⁰-θ)

  Fx : horizontal plane

  Fy : vertical plane
• Elasticity : Ability of an object to return to its original size and shape when force acting on it is removed.
• Hooke's Law: Extension of a spring is directly proportional to the stretching force if elastic limit of spring is not exceeded.
• Factors affecting spring constant, k:

  • material : strong (stiffer) material, larger k ; steel > copper
  • length : longer spring, smaller k ; shorter > longer
  • diameter : larger diameter, smaller k ; small > large
  • thickness : thicker spring, larger k ; thick > thin