BRAINCAKE

Global challenges

OCR GCSE PhysicsTopic 8 of 828 lessons

Revision notes for Global challenges in OCR Physics A (J249). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.

  1. Typical speeds in everyday lifeKnowing typical speeds helps you check that an answer is sensible.
  2. Estimating everyday accelerationsAcceleration is the change in speed divided by the time taken.
  3. Converting units and calculating ratesSpeeds are often given in kilometres per hour (km/h) or miles per hour (mph), which are non-SI units.
  4. Measuring human reaction timesYour reaction time is the time between a stimulus, such as seeing something happen, and your response to it.
  5. Stopping distances and road safetyWhen a driver sees a hazard, the car does not stop at once.
  6. Stopping distance and speedStopping distances for a typical car on a dry road are given in the Highway Code.
  7. The dangers of large decelerationsWhen a vehicle slows down, its speed decreases.
  8. Estimating forces on a public roadTo estimate a force on a road, choose a sensible mass for the vehicle, choose a sensible acceleration, then use force = mass × acceleration.
  9. Estimating speeds, accelerations and forces in road transportTypical speeds to use in estimates are walking 1.5 m/s, running 3 m/s, cycling 6 m/s, a car in a town at 30 mph which is about 13 m/s, and a car on…
  10. Energy sources on EarthThe main energy sources we use on Earth are fossil fuels (coal, oil and natural gas), nuclear fuel, biofuel, wind, hydroelectricity, tides and the…
  11. Trends in energy resource useOver the last 150 years the total amount of energy people use has increased.
  12. The national gridThe national grid is a network of cables and transformers that connects power stations to homes, schools, shops and factories all over the country.
  13. Step-up and step-down transformersA transformer changes the potential difference of an electrical supply.
  14. Why the grid is efficientWhen current flows through a cable the cable heats up.
  15. Transformers and power transferA transformer has a primary coil and a secondary coil wound on an iron core.
  16. Domestic mains supply in the UKThe electricity supply to homes in the UK is alternating current, written a.c.
  17. Direct and alternating potential differenceA cell or battery gives a direct potential difference, written d.c.
  18. Live, neutral and earth wiresMains cables have three wires, each with a different job and a different colour of insulation.
  19. Dangers of the live wire and earth connectionsA switch in a mains circuit should always be in the live wire.
  20. Red-shift and the expanding universeLight from a star or galaxy contains a pattern of dark lines at particular wavelengths.
  21. Red-shift, CMBR and the Big BangThe Big Bang model says that the universe began about 14 billion years ago from a single point that was extremely small, hot and dense.
  22. Formation of the Sun and stability of starsOur Sun was formed from a huge cloud of dust and gas called a nebula.
  23. Thermal radiation from all bodiesAll objects emit electromagnetic radiation, whatever their temperature.
  24. The Solar System and satellitesThe Solar System has the Sun, which is a star, at its centre.
  25. Circular orbits: speed and velocityVelocity is a vector, so it has both a size (the speed) and a direction.
  26. Orbital speed and radiusA planet, moon or satellite stays in a stable orbit when gravity is exactly the pull needed to keep it moving round in a circle.
  27. Temperature and radiation balanceAll bodies absorb radiation from their surroundings and emit radiation of their own.
  28. Waves exploring hidden structuresWaves can be used to explore structures we cannot see directly, such as the inside of the Earth or the deep sea.

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