chapter 9 Forces

• Earthquakes occur when a plate slides over another plate, releasing a large amount of energy
• Tsunamis occur due to vigorous movement of the ocean floor, converting potential energy to kinetic energy and hitting the shore with great force
• Contact force is the force acting between two objects in contact
• Non-contact forces act between two objects not touching each other
• Friction force: contact force

  • Opposes motion between two surfaces in contact
• Elastic force: contact force

  • Acts on a stretched or compressed elastic object to return to its original shape
• Gravitational force: non-contact force

  • Attracts two objects towards each other
• Magnetic force: non-contact force

  • Exerted between a magnet and another magnetic material
• Weight is the gravitational force acting on an object
• Mass is the amount of matter in an object
• Energy can:

  • Move a stationary object
  • Change the speed of an object
  • Change the direction an object moves in
  • Stop a moving object
• Changes due to the turning effect of a force:

  • Applying a downward force results in a turning effect about a fixed point
• Changes in size or shape of an object can occur due to the transfer of energy between objects
• Changes in pressure:

  • Pin with small area of contact experiences high pressure and is pushed in easily
  • Nail with large area of contact experiences low pressure and is pushed in with difficulty
• Calculating pressure:

  • Pressure (N/m sq) = force (N) / area (m sq)
• Atmospheric pressure decreases higher above sea level due to lesser air particles pushing down
• Work done when energy is transferred, measured in joules (J)
• For work to be done:

  • Force is applied on the object
  • The object moves
  • The object moves in the same direction as the force applied
• Fossil fuels:

  • Formed from remains of dead plants and animals buried millions of years ago
  • Limited and will run out
  • CPE > HE > KE > EE
• Alternative sources to generate electricity:

  • Solar energy
  • Hydroelectric energy
  • Wind energy
  • Geothermal energy
  • Biofuel
  • Nuclear energy
• Solar energy:

  • Captures sunlight and converts light energy into electrical energy
  • LE > EE
• Hydroelectric energy:

  • Electrical energy generated by turbines powered by moving water
  • GPE > KE > KE > EE
  • Requires a lot of space
• Wind energy:

  • Kinetic energy of the wind transferred to turbine blades to generate electricity
  • KE > KE > EE
• Geothermal energy:

  • Uses heat stored in the earth to boil water
  • HE > KE > KE > EE
• Biofuels:

  • Made from animal waste or plant materials inedible by humans
  • CPE > HE > EE
• Nuclear energy:

  • Energy harnessed from the nucleus of an atom
  • nuclear energy> HE > KE > EE