P8

• acceleration = change in velocity / time taken
• Large deceleration can be dangerous

  • large deceleration requires a large force
  • force can be lowered by slowing the object down over a linger time
  • The longer for a change in momentum- the smaller the force
• Safety features to reduce the force

  In cars

  • seatbelts and airbags slow down gradually
  • crumple zones- front and back of cars which crumple easily to increase the time taken to stop

  Bike

  • helmets containing crushable layers of foam to increase time taken for head ti stop
  • Shin pads- pad deforms to reduce deceleration and force
• Stopping speed = Thinking distance + Braking distance
• Thinking distance

  • distance the car travels in the drivers reaction time
  • affect by:

  > reaction time: tiredness, alcohol, drugs and distraction

  > speed- the faster you're going, the further you'll travel during reaction time
• Braking distance

  • distance taken to stop once breaks have been applied
  • Affected by:

  > speed- the faster, the further it takes to stop

  > the mass- car full of people and luggage can't stop ad quickly

  > condition of breaks- worn or faulty breaks won't be able to break with as much force

  > grip of tyres- minimum tread depth of 1.6mm
• Ruler dropping experiment

  1. stand with hands open- get someone else to hold the ruler so it hangs between thumb and forefinger
  2. without any warning the person drops the ruler and close finger and thumb to try and catch ruler as quickly as possible
  3. measurement on the ruler at the point it is caught is how far the ruler is dropped in the time it took you to react
  4. the longer the distance, the longer the reaction time
  5. hard to do the reaction accurately so do lots of repeats to find mean distance
• Stopping safely

  • typical stopping distance are from the Highway Code
  • leave enough space so driver can stop safely
  • Speed limits are important because speed affects stopping distance
  • As speed increases, thinking distance increases at the same rate because drivers reaction time will stay constant
  • braking distance and speed have a squared relationship
• non renewable energy source

  source that is limited and damages the environment

  • coal.oil and natural gas , nuclear fuels (uranium and plutonium)
• Power station

  1. fossil fuels burns (in oxygen) the energy in its chemical store is transferred to the thermal store of water
  2. Water boils and forms steam
  3. steam turns the turbine
  4. turbine is connected to generator (big alternator)
  5. generator transfers energy electrically away from power station via national grid
• Nuclear reactors

  • Nuclear fission energy heats water

  1. water turns to steam
  2. drives turbine

  • nuclear takes the longest to start up
  • boiler contains uranium fuel rod
• Non-renewabl sources cause environmental problems

  • coal, oil, and natural gas release Co2 - contributes to global warmongering and climate change
  • Burning coil and oil releases sulfur dioxide which causes acid rain that erodes buildings
  • coal mining- makes a mess of landscape
  • Oil spillages- series environmental problems
  • Nuclear waste- had and expensive to dispose
• Renewable sources

  • bio-fuels
  • wind power
  • Sun
  • hydro-electricity
  • tides
• Bio-fuels

  • farm waste, animal droppings, landfill rubbish, especially grown crops: sugar canes, veg oil and trees
  • Grow more - renewable
  • burnt to produce electricity or fuel cars
  • reliable as crops grow quick but not immediate
  • Carbon neutral- if plants grow at the same rate they are destroyed
  • expensive to grow and may lead to a decrease in crops grown for people and an increase in food prices
  • Species lose habitat as land is cleared off for biofuels
• Windpower

  • rotating blades turns generator= electricity
  • no solution
  • spoil view , noisy and relies on wind
• Solar cells

  • Special material that releases electrons when light falls upon them generating electrical current
  • used in remote places
  • no pollution - a lot of energy to make
  • Generate small amounts of electricity
  • Best used for sunny countries
  • Can't make solar power at night or when there is high demand
• Hydro-electricity

  • build dams- flood valley
  • rainwater caught- turns turbines through flood
  • loss habitat, initial high cost
  • Immediate more water= more electricity, minimal running costs, reliable
• Tidal barrages

  • Big dams over river estuaries
  • Containing turbines
  • tide runs through and turns turbine= electricity
  • No pollution
  • limits boat access and alters habitats
  • Tides are reliable, height is a variable
• Why non-renewable

  • population growth- increased electricity use
  • Mostly generates by fossil fuels and nuclear power
  • Fossil fuels will run out and is damaging the environment
  • Slow progress in investment of renewable

  > Water dependent

  > Produces less

  > population must try to use less

  > investigate alternatives
• Uk mains 


  50 Hz

  230V

  A.C
• National grid

  • network of wires and transformers
  • Powerstation to consumer
  • high current lose energy as wires heat up and energy is transferred into thermal energy into the surroundings
  • wires act as resistors
  • boost p.d high 400 000 V to keep current low to travel efficiently
  • Wasted energy costs money
• Alternating current

  • produced by alternating voltage : P.d + current change directions
• Direct current

  • direct voltage
  • P.d and current don't change direction
• Transformers

  • two coils (primary and secondary)
  • Joined by iron core (magnetic induction)
  • P.d increase in step up, more turns on second than primary
  • Reduced for local consumers using step down- more turns on primary coil than secondary
  • Power supplied = p.d (V) x Current (A)
• Three wires in plug- Live wire

  • brown
  • carries alternating voltage from power supply of 230v
  • body is at 0V - large p.d between live wire and body and can electrocute a person as current flows through
• Three wires in plug- Neutral wire

  • blue
  • completes the circuit
  • current flows through live and neutral wire
  • 0V
• Three wires in plug- Earth wire

  • green and yellow
  • for safety
  • Carries current away if something goes wrong
  • 0V
• How to prevent casualties - earth wire

  • electricity flows through anything that conducts electricity e.g metal - current would be induced - electric shock and fires
  • Appliances with metal cases must be 'earthed' for safety - case attached to earth wire so current would pass through metal to earth wire
  • Earth wire is thick and gives low resistance- total resistance decreases so current passes through live wire, metal and earth wire
• How to prevent casualties - fuse

  • Surge in current melts fuse- breaking the circuit and cutting off supply and isolates the appliance
  • Fuses and earthing protect the circuits and wiring in appliances from getting fried
• how to prevent casualties- double insulated

  • non-conductive casing
  • Doesn't need an earth wire
• Solar system - made up of

  • Star- huge ball of gases undergoing nuclear fusion and emitting heat and light
  • Planet- large, spherical mass that orbits a star
  • Dwarf planet- masses which orbit stars, smaller than planets
  • Natural satellites- moons and other objects that orbit planets
  • Comet- travelling ball of dust and ice
  • Asteroid- Rock in space
  • Meteors- rocks that burn up on entry to earth
• Satellites- geostationary orbit

  • high orbit around the earth's equator and orbit once every 24 hours
  • Stay above same point on earth's surface because earth rotates with them
  • ideal for communications as they stay at same point above earth
• Satellites om polar orbits

  • sweep low over both poles whilst earth rotates beneath them
  • much closer to earth and move much faster
  • orbit quickly- less than 2 hrs
  • scan the next but of earth- allowing each bit to be monitored
  • used for weather, mapping and surveillance
• Gravity

  • Travelling in a circle- constantly changing direction
  • Velocity is constantly changing and acceleration
  • Centripetal force- force directed In centre of circle
  • object keeps accelerating but velocity is on a right angle that makes it travel in a circle
  • For an orbit to stay stable the object must be moving at a right speed
• How to remain stable

  • closer to star or planet- stronger the gravitational force
  • Stronger the force- the faster the orbiting object needs to be going to avoid falling
  • closer, the faster too stay in orbit
  • Moves faster, smaller radius
  • Moves slower, larger radius
• Galaxy

  • a region of space containing stars
  • when white light passes through a spectrum it refracts at different speeds - a rainbow is produced
• Redshift

  • source is moving away from you
  • The greater the redshift , the faster away from the source of light is moving away
• Blue shift

  • Source moving towards you
• Doppler effect

  • Squashing or stretching of wave as the source of the waves moves either towards or away from you
• Origins of the universe: Big bang

  • creation of the universe
  • Expansion of universe
  • 14 billion years ago, single infinitely dense point
  • Space is expanding at every point, no matter where you are
  • Always appears you're at the centre of the universe, even though you're not