Application of force

• Forces

  Whenever we push or pull an object, we are said to exert a force
• Effects of forces


  • Start an object moving
  • Stop a moving object
  • Change the speed of a moving object
  • Change the direction of a moving object
  • Change the size and shape of an object
• Measurement of forces

  • Instrument: force-meters (eg. Spring balances)
  • SI unit: newton (N)
• Speed

  • A measure of how fast someone or something moves
  • SI unit: metre per second (m/s)
• Speed formula

  1. Speed = Distance

  2. Time

  
• Kinds of forces

  • Contact forces (A force that acts when objects touch)
  • Non-contact forces (A force that acts at a distance from an object)
• Friction

  • Friction acts whenever one surface rubs against another surface
  • Friction causes surfaces to heat up
  • Friction always opposes the movement of an object
• Ways to reduce friction


  • Use smooth surfaces (lanes in bowling alleys)
  • Use ball bearings (used in moving parts of machines)
  • Lubrication (like grease and oil)
  • Streamlining (eg. Shape of an aircraft)
• Magnetic force

  • Magnets exert a force called magnetic force
  • magnetic force is a non-contact force
  • Like poles repel, unlike poles attract
• Gravitational force (Gravity)

  • the force that pulls objects towards the earth
  • Gravity exists between any two objects with mass
  • Gravity is a non-contact force
• Weight

  • A measure of the force of gravity exerted on an object
  • The heavier an object, the greater the force acting on it
  • Unit of weight: newton
• Mass

  • Measure of the amount of matter in an object
  • SI unit = kg
• Pressure


  • The measure of the amount of force acting on a unit area
  • SI unit: pascal (Pa)
• Pressure in liquids and gases

  • Liquids: the deeper you go, the higher the water pressure
  • Gases: the higher you go (atmosphere), the lower the air pressure
• Examples (change in air pressure)

  • Squishing a drink box
  • Holding a suction cup on the wall
• Pressure formula

  • Pressure = Force/Area
  • Area
• Destructive forces of nature


  • Earthquakes
  • Tsunamis
  • Volcanoes
  • Typhoons