physics:moving things

• Speed

  How fast something is travelling, measured by distance travelled and time taken
• Units for speed

  • km/h
  • m/s
  • mph
• Actual speeds during a journey can be faster or slower than the mean speed
• Moment

  A turning force, measured in newton metres (N m)
• Calculating moment

  moment (in N m) = force (in N) × perpendicular distance from the pivot (m)
• The longer the distance, the greater the moment
• If a machine makes it possible to lift or move a load using a smaller force, the force has to move through a greater distance
• Calculating work


  work = force × distance moved in the direction of the force
• Friction

  • Can be reduced using rollers or wheels
• Water resistance and air resistance


  Forms of drag
• Size of drag force

  Increases as the speed of the object increases
• As a ship gets faster


  The water resistance increases
• Eventually the water resistance is as large as the force from the sails

  The ship cannot accelerate any more and is now at its top speed for that amount of wind
• Energy needed by humans and animals

  Comes from their food
• Energy in food


  Originally came from the Sun
• Kinetic energy


  Energy possessed by anything that is moving
• Coal


  A fossil fuel, formed underground over millions of years from the remains of plants
• Fossil fuels

  • Very convenient way of storing large amounts of energy
  • Non-renewable resource because they will run out one day
• Some forms of transport started to use energy stored in coal

  Over 200 years ago
• Coal

  A fossil fuel, formed underground over millions of years from the remains of plants
• Today we also use energy stored in oil and natural gas for transport
• Elastic potential energy (or strain energy)

  Energy stored in a wound-up spring
• There is more internal (thermal) energy in things that are hot
• Many modern devices use energy transferred by electricity
• Electricity cannot be stored, but has to be generated using renewable resources such as wind, moving water or solar energy, or from non-renewable resources such as fossil fuels or nuclear energy
• Energy is not always transferred usefully
• Wasted energy is usually transferred to the surroundings by heating, and often by sound as well
• The greater the efficiency, the less energy is wasted
• Speed


  A way of saying how far you can travel in a certain time
• Time units for speed

  • Second (s)
  • Minute (m)
  • Hour (h)
  • Longer
• Calculating speed


  1. Measure distance

  2. Measure time

  3. Distance / Time
• Speed units


  • Miles per hour (mph)
  • Kilometres per hour (km/h)
  • Metres per second (m/s)
• Many moving objects do not travel at a constant speed
• Cars travel faster on motorways than in town

  Cars may have to stop at junctions
• Mean (average) speed


  Total distance travelled / Total time taken
• Distance-time graph


  Shows how fast someone travelled during a journey
• Distance-time graph


  • Steep line = moving quickly
  • Shallow line = moving slowly
  • Horizontal line = not moving
• Lever

  A long bar that turns around a pivot or fulcrum
• Using a lever

  1. Push down on one side to apply an effort

  2. Object on the other end moves up

  3. This object is called the load

  4. The longer the lever, the easier it is to move the load
• Equilibrium

  A state of balance where the clockwise moment is balancing the anticlockwise moment