Topic 9 - Forces

• Non-contact forces


  Forces that act on objects without physical contact
• Types of non-contact forces

  • Gravitational force
  • Electrostatic force
  • Magnetic force
• Gravitational force


  Force of attraction between objects due to their mass
• Electrostatic force


  Attraction or repulsion between electric charges
• Magnetic force


  Attraction or repulsion between magnetic poles
• Contact forces


  Forces that require physical connection between objects
• Normal contact force


  Force perpendicular to a surface
• Friction


  Force that opposes the relative motion between two surfaces in contact
• Lubrication can reduce energy loss due to friction
• Vectors


  Quantities with both magnitude and direction
• Vector addition


  1. Draw first vector

  2. Draw second vector

  3. Add vectors head-to-tail

  4. Resultant vector is from tail of first to head of last
• Free body force diagram


  Shows all forces acting on a single object
• Forces on an airplane


  • Thrust
  • Drag
  • Lift
  • Weight
• Moment


  Turning effect of a force, equal to force x perpendicular distance
• Archimedes said "Give me a lever and a place to stand and I can move the Earth"
• Lever examples


  • Spanners
  • Seesaws
  • Spades
  • Hammers
  • Wheelbarrows
• Gear ratio


  Ratio of rotations between two gears