P8

• Speeds


  • Wind: 5 - 7 m/s
  • Sound: 340 m/s
  • Walking: 5 km/h (~1.4 m/s)
  • Running: 6 miles/hour (~3 m/s)
  • Cycling: 15 km/h (~4m/s)
  • Bus: 14 km/h
  • Train: 125 miles/hour
  • Plane: 900 km/h
• Acceleration


  a = F/m
• Converting Units


  Convert the answer one unit at a time
• Human Reaction Time


  • Delay between observing an event and acting due to processing by the brain
  • Average human reaction time is 0.25 seconds (250 milliseconds)
• Factors affecting Thinking Distance

  • Speed
  • Reaction time
  • Concentration
  • Tiredness
  • Distractions
  • Influence of drugs/alcohol
• Factors affecting Braking Distance

  • Speed
  • Poor road conditions (icy, wet)
  • Bald tires (low friction)
  • Worn brake pads
  • Weight (more passengers)
• Speed


  Greater speed leads to greater braking distance
• When braking hard, there is a large deceleration and therefore a large force exerted on the passengers and the vehicle, which can be dangerous and cause injury
• Seatbelts


  • Strap you in, but also stretch slightly under large forces
  • This increases the distance moved for passengers to stop, decreasing the magnitude of the acceleration and reducing the force experienced
• Crumple Zones


  • Softer areas at the front of the car which crumple upon impact, absorbing energy and increasing the time taken for the car to stop, reducing the acceleration and force on passengers
• Airbags


  • Inflate instantaneously upon a crash, causing your head to hit the airbag and slow down, increasing the time taken for the head to stop moving and reducing the force on the neck
• Main Energy Sources


  • Fossil Fuels
  • Nuclear Fuels
  • Biofuels
  • Wind
  • Hydroelectricity
  • Tidal
  • Solar
• Energy consumption was very low before 1850, then saw a sharp rise in coal use due to the industrial revolution, followed by a rise in extraction of fossil fuels and crude oil, and more recently an increase in nuclear power and renewable energy
• The National Grid


  Electrical power is transferred at high voltages from power stations for domestic use via overhead power lines, with step-up transformers used to increase the potential difference and reduce current, and step-down transformers used to decrease the potential difference and increase the current for domestic use
• Mains Electricity


  Alternating current (AC) at 50Hz and 230V, varying from a positive maximum to a negative minimum
• Direct Electricity


  Constant fixed (positive) amount, provided by batteries and cells
• Wiring in a Plug

  • Live Wire (brown, carries voltage from mains to appliance)
  • Neutral Wire (blue, completes the circuit)
  • Earth Wire (green and yellow striped, safety wire to stop the appliance becoming live)
• The earth wire is connected to the metal casing of the appliance, so if the live wire touches the casing, the current will go through the earth wire to the ground instead of through the user
• Red Shift


  Light appears 'red shifted' from galaxies which are moving away from Earth, evidence of an expanding universe
• Big Bang Theory


  The universe started from a single point and has been expanding ever since, as evidenced by red shift and cosmic microwave background radiation
• Red shift


  Shows the universe is expanding
• The universe must have been formed from a single point initially
• Cosmic Microwave Background Radiation (CMBR)


  Radiation present wherever you point a telescope in the sky, proving the hot young universe has cooled and expanded since
• Life cycle of a star

  1. Dust and gas clouds present in galaxy

  2. Gravitational attraction draws them together, increasing temperature and pressure

  3. Fusion occurs as lighter nuclei fuse to form helium, releasing energy

  4. Equilibrium forms where energy released balances gravitational collapse

  5. Star forms and stays in this balanced state for billions of years

  6. Star runs out of gas to fuse, collapses, and may become a supernova, neutron star or black hole

  7. If average size, star collapses and becomes a planetary nebula and white dwarf
• Radiation emission


  Intensity and wavelength distribution depends on temperature of body
• Order of planets in solar system

  • Mercury
  • Venus
  • Earth
  • Mars
  • Jupiter
  • Saturn
  • Uranus
  • Neptune<|(Pluto)
• Planets


  • Smaller planets (Mercury, Venus, Earth, Mars) are made of primarily rock
  • Larger planets (Jupiter, Saturn, Uranus, Neptune) are primarily gas
• Planets


  • All orbit the Sun on the same plane
  • All rotate on their own axis at different speeds
  • Some rotate in opposite direction or on skewed axis due to past collisions
• Larger planets


  • Tend to have rings, as their strong gravitational field attracts debris that then orbits the planet
• Moons


  Natural satellites, objects which orbit a planet, formed naturally
• Our Moon was formed very early on in the solar system's lifetime, from debris ejected when a large mars-sized object collided with the Earth
• Satellites


  • Artificial satellites, placed into orbit by humans on purpose
  • Can be in polar orbit for surveillance and weather forecasting, or geostationary orbit for communications
• As a planet orbits the Sun

  Gravitational force causes the planet to change direction constantly, but its speed remains constant
• If a planet moves closer to the Sun

  Gravitational attraction increases, force and acceleration increase, so orbital speed increases
• Temperature of a body

  Due to balance between incoming radiation absorbed and radiation emitted
• Earth's temperature is constant over a long time period, due to a balance between radiation transmitted through the atmosphere and absorbed by greenhouse gases
• As greenhouse gases increase, more radiation is absorbed than emitted, causing global warming
• P waves and S waves

  • P waves are longitudinal, travel quicker, and can pass through solids and liquids
  • S waves are transverse and can only pass through solids
• P waves can be detected on the other side of the Earth, but no S waves reach there, suggesting the Earth's core is liquid
• SONAR


  Used to map the ocean floor by sending sound waves down and measuring the time taken for them to reflect back