(12)Intro to forces

• States of Motion

  • Objects at rest
  • Objects moving at constant speed
  • Objects either speeding up or slowing down (ie accelerating or decelerating)
• Different states of motion

  • At rest
  • Travelling at constant speed in same direction
  • Travelling in one direction with uniformly increasing speed (ie. constant or uniform acceleration/ accelerating)
  • Travelling in one direction with uniformly decreasing speed (ie. constant or uniform deceleration/ decelerating)
• Force

  A push or pull that changes or tends to change the state of motion of an object on which it acts
• If a force acts on a stationary body it can get it moving
• If a force acts on a moving body it can either increase its speed or decrease its speed
• Force as a Vector Quantity

  Force has magnitude (size) as well as direction
• Representing force on paper

  • Use an arrow to show the magnitude (size) and direction of the force
• Unit of measuring force

  Newtons (N)
• Newton is not a Base Unit, it is a derived unit
• Types of forces

  • Contact Forces
  • Non-contact Forces
• Contact Force

  Any force that occurs as a result of two (or more) objects making contact with each other
• Non-contact Force

  A force which acts on an object without coming physically in contact with it
• Balanced Forces

  Forces acting on an object have equal strength and act in opposite directions, effectively cancelling each other out
• Friction is a contact force
• Applying forces to get them balanced

  Determine the size and direction of the force(s) needed to balance the existing forces
• Unbalanced Forces

  The force applied in one direction is greater than the force applied in the opposite direction
• Determining unbalanced forces

  Work out the size and direction of the unbalanced force acting on each object