Motion, forces and conservation of energy

• Scalar quantity has magnitude

  (size) but Vectors have magnitude and direction
• scalar quantity

  speed

  distance

  time

  energy

  mass
• vector quantity

  displacement

  velocity

  acceleration

  weight

  momentum
• on a velocity time graph, displacement is calculated by the area under a velocity time graph

  area of triangle, rectangle or trapezium
• Acceleration of an object down a slope

  2 light gates

  measure time taken for object to pass the 1st then 2nd light gate

  electronic timer to measure time

  mask is placed above the trolley so it cuts the beam

  mask is measured in m using a ruler
• Walking - 1.5 m/s

  Running - 3 m/s

  Cycling - 6 m/s
• Newton’s first law

  an object remains in the same state unless a force acts upon it
• Newtons second law F=mv-mv over t!!!

  inertial mass is how difficult it is to change the velocity of an object
• Newtons 3rd law- When two objects interact the exert equal and opposite forces in each other

  example: non contact

  the earth pulls the satellite

  the satellite pulls the earth
• F= ma practical

  Independent- force

  Dependent- acceleration

  Control -mass
• Attach a bench pulley to the end of the bench

  put a mass on the car

  tie string on the car and extend to the end of the bench

  make sure the string is parallel to bench
• Factors that affect stopping distance of a vehicle

  mass and speed

  drivers reaction time

  State of vehicles brakes

  state of the road surface

  friction between tyre and surface
• Factors affecting reaction time

  tiredness

  drugs/alcohol usage
• Stopping distance= thinking distance+ braking distance
• How do you measure reaction time

  drop ruler experiment

  One person holds the ruler at the top, and one person holds the wall at the bottom. The person holding the ruler at the top, drops the ruler with no warning.

  repeat and calc average
• Dangers of large decelerations

  object decelerates=momentum is lost, force increases

  injuries- whiplash, brain and spine il

  Prevent LD- breaking earlier, driving at a slower speed, this reduces force

  crumple zones
• A stationary object has a momentum

  of 0
• Conservation of energy: cannot be created or destroyed but energy can be transferred, or dissipated
• When there are energy transfers in a closed system there are no change in the total energy
• energy transfers

  heating, mechanical, radiation

  and electrical
• How do you reduce unwanted energy transfer?

  Thermal insulation

  thick double sided walls have a low thermal conductivity

  Lubrication

  Friction leads to unwanted thermal energy

  oil reduces friction
• Convection

  Heat loss through gases and liquids eg foam seals reduce heat loss by convection
• Conduction


  Heat loss through solids

  eg

  double glazed windows reduces thermal conductivity
• how can efficiency be increased

  minimise energy input by maximising energy output by:

  reducing friction, improving mechanical designs (housing) using more efficient energy sources.
• Uses of fossil fuels

  Burned to provide heat

  cooking

  powering engines

  generate electricity
• Pros of fossil fuels

  Relatively cheap

  used in any conditions

  transport is designed to run using fossil fuels
• Cons

  They will run out- limited resource

  produces carbon dioxide when burned which is a greenhouse gas and contributes to global warming

  produces toxic gases like carbon monoxide
• Nuclear energy is obtained from the decay of unstable nuclei in nuclear power stations uses- generate electricity
• Nuclear energy

  👍do not produce pollutants like co2

  Cheap to maintain

  unlikely to run out

  👎expensive to set up and decommission

  produces radioactive so must be stired carefully

  nuclear disaster

  terrorism
• Biofuels are made from recently living organisms

  👍 a renewable resource

  easy to transport

  • 👎you need somewhere to grow plants, deforestation release co2
• Uses of biofuels: used in existing vehicles
• Wind and solar power

  👍 cheap to maintain

  do not produce pollutants

  👎 expensive to set up

  takes up land space

  weather dependent
• Solar power is generated by solar cells or panels, which can generate electricity directly from sunlight
• Wind turbines, convert, the kinetic energy from the wind into electrical energy
• Hydroelectric dams

  traps water that comes upstream

  trapped water accumulates into a reservoir high above

  reservoir has a high amount of GPE which can be converted into electricity

  👍reliable, produces energy quickly, no pollution, cheap to maintain

  👎 flooding, expensive to set up