Exam Notes on Resultant Force and Motion

Resultant Force

  • Determine the resultant force.
  • State the effects of a resultant force.
  • An object remains at rest or continues in a straight line at constant speed unless acted on by a resultant force.

Balanced and Unbalanced Forces

  • Forces are unbalanced when unequal in size and act in the same or opposite directions.
  • A resultant force may change an object's velocity by altering its direction or speed.
  • Forces are balanced when equal in size and opposite in direction.
  • When forces are balanced, the resultant force is zero.

Newton’s First Law of Motion

  • Objects remain at rest or move with constant velocity unless acted on by a resultant force.
  • If the resultant force is zero:
    • Stationary objects remain stationary.
    • Moving objects continue at the same velocity.
  • When the resultant force is not zero:
    • The speed of the object can change.
    • The direction of the object can change.

Newton’s Second Law of Motion

  • The acceleration of an object is proportional to the resultant force and inversely proportional to its mass.
  • Equation: F=maF = ma
    • F = resultant force (N)
    • m = mass (kg)
    • a = acceleration (m/s²)

Uniform Circular Motion

  • When an object travels in circular motion, its direction constantly changes.
  • Velocity changes, even if speed is constant.
  • Circular motion is a type of acceleration.

Direction of Force

  • The resultant force is always directed towards the center of the circular path.

Factors Affecting Uniform Circular Motion

  • Centripetal force keeps objects moving in a circular path.
  • Depends on:
    • Mass: Greater mass requires greater force (speed and radius constant).
    • Speed: Faster object requires greater force (mass and radius constant).
    • Radius: Smaller radius requires greater force (speed and mass constant).

Friction

  • Friction opposes motion, slowing objects down. Energy is transferred by heating, increasing temperature.
  • Solid friction:
    • Decreases speed.
    • Increases temperature.
    • Reduced by lubricating or smoothing surfaces.
  • Air resistance: slows objects moving through air.
    • Reduces speed and increases temperature.
  • Fluid friction reduced by streamlining object shape.