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An example question…

An example question…. 03/01/2020. This car can apply a maximum braking force of 10,000N. If the car’s mass is 1000Kg how far is its stopping distance when it is travelling at a speed of 15m/s (roughly 30mph) and 30m/s (roughly 60mph)?. 15m/s = 11.25m stopping distance

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An example question…

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  1. An example question… 03/01/2020 This car can apply a maximum braking force of 10,000N. If the car’s mass is 1000Kg how far is its stopping distance when it is travelling at a speed of 15m/s (roughly 30mph) and 30m/s (roughly 60mph)? 15m/s = 11.25m stopping distance 30m/s = 45m stopping distance (4 times greater)

  2. A Practical Example of Doing Work Consider a rocket re-entering the Earth’s atmosphere: The rocket would initially have a very high _______ energy. This energy would then _____ due to friction caused by collisions with _______ in the atmosphere. These collisions would cause the rocket to ____ up (_____ is “being done” on the rocket). To help deal with this, rockets have special materials that are designed to lose heat quickly. Words – work, kinetic, particles, heat, decrease

  3. Energy Changes in Roller Coasters 1) Electrical energy is transferred into gravitational potential energy 3) Kinetic energy is transferred back into gravitational potential energy 2) Gravitational potential energy is transferred into kinetic energy

  4. Test questions… 03/01/2020 • Julia tries to run 100m in 12 seconds and succeeds. How fast did she run? • Isabelle accelerates at a rate of 2m/s2 for 3 seconds. If she started at 10m/s what was her final speed? • Jake decides to lift his book up into the air. His book has a mass of 100g and he lifts it 50cm. Calculate the work done. • Jamie accelerates from 0 to 10m/s in 5 seconds. If her mass is 60kg how much force did her legs apply? • Lily rides 1km at a speed of 20m/s. How long did the journey take? • Rob thinks it’s funny to push Jack with a force of 140N. If Jack has a mass of 70kg calculate his acceleration. • Vicky slams on the brakes on her bike and her brakes do 20,000J of work. If the combined mass is 100kg what speed was she travelling at? • Paddy has a mass of 75kg. If he accelerates from 10 to 20m/s in 2s how much force did he apply? 8.3m/s 16m/s 0.5J 120N 50s 2m/s2 20m/s 375N

  5. Test questions… 03/01/2020 • Bex amuses herself by throwing things at Kit. If she throws a ball with a speed of 20m/s and the distance between her and Kit is 5m how long will it take to reach him? • Dave throws calculators around the room with a force of 20N. If each calculator has a mass of 200g calculate the acceleration. • Max has a mass of 70kg. What is his weight on Earth, where the gravitational field strength is 10N/kg? • Kathryn does some work by pushing a box around with a force of 1N. She does 5J of work and decides to call it a day. How far did she push it? • On the moon Jake might weigh 112N. If the gravitational field strength on the moon is 1.6N/kg what is his mass? • Heather likes bird watching. She sees a bird fly 100m in 20s. How fast was it flying? • How much kinetic energy would Simon have if he travelled at a speed of 5m/s and has a mass of 70kg? 0.25s 100m/s2 700N 5m 70kg 5m/s 875J

  6. Topic 5 – Nuclear Fission and Nuclear Fusion 03/01/2020

  7. The structure of the atom 03/01/2020 ELECTRON – negative, mass nearly nothing PROTON – positive, same mass as neutron (“1”) NEUTRON – neutral, same mass as proton (“1”)

  8. The structure of the atom 03/01/2020 NUCLEON/MASS NUMBER = number of protons + number of neutrons 4 He SYMBOL 2 ATOMIC/PROTON NUMBER = number of protons (obviously)

  9. Introduction to Radioactivity Some substances are classed as “radioactive” – this means that they are unstable and continuously give out radiation at random intervals: Radiation The nucleus is more stable after emitting some radiation – this is called “radioactive decay”. This process is NOT affected by temperature or other physical conditions.

  10. Ionisation Radiation is dangerous because it “ionises” atoms – in other words, it turns them into ions by “knocking off” electrons:

  11. Types of radiation 03/01/2020 New nucleus 1) Alpha () – an atom decays into a new atom and emits an alpha particle (2 protons and 2 ______ – the nucleus of a ______ atom) Unstable nucleus New nucleus Alpha particle 2) Beta () – an atom decays into a new atom by changing a neutron into a _______ and electron. The fast moving, high energy electron is called a _____ particle. Beta particle Unstable nucleus 3) Gamma – after  or  decay surplus ______ is sometimes emitted. This is called gamma radiation and has a very high ______ with short wavelength. The atom is not changed. Words – frequency, proton, energy, neutrons, helium, beta Unstable nucleus New nucleus Gamma radiation

  12. Blocking Radiation    Each type of radiation can be blocked by different materials: Sheet of paper (or 6cm of air will do) Few mm of aluminium Few cm of lead

  13. Summary

  14. Nuclear power stations Nuclear fission reactions can be a source of energy, like in a nuclear power station:

  15. Nuclear fission 03/01/2020 More neutrons Neutron Unstable nucleus Uranium or plutonium nucleus New nuclei (e.g. barium and krypton)

  16. Chain reactions 03/01/2020 Each fission reaction releases neutrons that are used in further reactions.

  17. Nuclear power stations Notice that the heat from these reactions is used to heat water and turn it into steam, which then drives turbines.

  18. Fission in Nuclear power stations These fission reactions occur in the fuel rods and they become very hot. Water cools the rods (which then turns to steam) and the control rods (made of boron) are moved in and out to control the amount of fission reactions taking place. This is called a Pressurised Water Reactor (PWR) How are control rods used to control the rate of these reactions?

  19. Nuclear Fusion in stars 03/01/2020 Proton Neutron Nuclear fusion basically combines smaller nuclei to make larger nuclei. It happens in stars but it’s not possible to use it in power stations yet as it needs temperatures of around 10,000,000OC. At lower temperatures, electrostatic repulsion of protons occurs (i.e. they repel each other due to their positive charges).

  20. Cold Fusion In 1989 we claimed that we had enabled “cold fusion”, i.e. we had created fusion reactions in lab temperatures. However, no one else could verify our findings so our theories have not been accepted. Stanley Pons and Martin Fleishmann

  21. Topic 6 – Advantages and Disadvantages of using Radioactive Materials

  22. Background Radiation 03/01/2020 13% are man-made Radon gas Food Cosmic rays Gamma rays Medical Nuclear power Notice that the amount of radon gas in the atmosphere varies according to location so some areas in the UK are more radioactive than others!

  23. Background Radiation by Location In 1986 an explosion occurred at the Chernobyl nuclear power plant. Here is a “radiation map” showing the background radiation immediately after the event: Other “risky” areas could be mining underground, being in a plane, working in an x-ray department etc

  24. Uses of radioactivity 1 Sterilising medical instruments Gamma rays can be used to kill and sterilise germs without the need for heating. The same technique can be used to kill microbes in food so that it lasts longer.

  25. Uses of radioactivity 2 - Tracers Gamma source A tracer is a small amount of radioactive material used to detect things, e.g. a leak in a pipe: The radiation from the radioactive source is picked up above the ground, enabling the leak in the pipe to be detected. Tracers can also be used in medicine to detect tumours: For medicinal tracers, you would probably use a beta source with a short half life – why?

  26. Uses of radioactivity 3 – Smoke Detectors Alpha emitter +ve electrode -ve electrode If smoke enters here a current no longer flows Ionised air particles Smoke detectors Alarm

  27. Uses of radioactivity 4 – Determining thickness Beta detector Paper Rollers Beta emitter

  28. Uses of Radioactivity 5 - Treating Cancer High energy gamma radiation can be used to kill cancerous cells. However, care must be taken in order to enure that the gamma radiation does not affect normal tissue as well. Radioactive iodine can be used to treat thyroid cancer. Iodine is needed by the thyroid so it naturally collects there. Radioactive iodine will then give out beta radiation and kill cancerous cells.

  29. A radioactive decay graph 03/01/2020 “1 Becquerel” means “1 radioactive count per second” Activity (Bq) Time

  30. Half life = radioisotope = new atom formed The decay of radioisotopes can be used to measure the material’s age. The HALF-LIFE of an atom is the time taken for HALF of the radioisotopes in a sample to decay… After 2 half lives another half have decayed (12 altogether) After 3 half lives another 2 have decayed (14 altogether) After 1 half life half have decayed (that’s 8) At start there are 16 radioisotopes

  31. A radioactive decay graph 1 half life 1 half life 1 half life Count Time

  32. Dating materials using half-lives 1 half life later… 1 half life later… 1 half life later… 2 1 8 4 8 8 8 8 Question: Uranium decays into lead. The half life of uranium is 4,000,000,000 years. A sample of radioactive rock contains 7 times as much lead as it does uranium. Calculate the age of the sample. Answer: The sample was originally completely uranium… …of the sample was uranium Now only 4/8 of the uranium remains – the other 4/8 is lead Now only 2/8 of uranium remains – the other 6/8 is lead Now only 1/8 of uranium remains – the other 7/8 is lead So it must have taken 3 half lives for the sample to decay until only 1/8 remained (which means that there is 7 times as much lead). Each half life is 4,000,000,000 years so the sample is 12,000,000,000 years old.

  33. An exam question… Potassium decays into argon. The half life of potassium is 1.3 billion years. A sample of rock from Mars is found to contain three argon atoms for every atom of potassium. How old is the rock? (3 marks) The rock must be 2 half lives old – 2.6 billion years

  34. Ionisation 03/01/2020 Radiation is dangerous because it “ionises” atoms – in other words, it turns them into ions by “knocking off” electrons: Alpha radiation is the most ionising (basically, because it’s the biggest). Ionisation causes cells in living tissue to mutate, usually causing cancer.

  35. Understanding Radioactivity over History • Task: Find out about the work of Marie Curie, including: • Which elements she discovered • Brief details of the work she did • What prizes she won • How her work eventually caused her death • How our understanding of radioactivity has changed due to her work

  36. Disposing of radioactive waste The containers are then kept in stores, often _________. The key to dealing with radioactive waste is to IMMOBILISE it. There are a number of ways of doing this depending on how __________ the waste is: High level waste is immobilised by mixing with ____ making ingredients, melting and pouring the glass into steel containers. Intermediate waste is set in cement in _____ drums. Words – glass, steel, underground, radioactive

  37. Nuclear Power Stations Advantages Disadvantages Don’t produce greenhouse gases Risk of accident Radioactive waste Why use nuclear power? Low levels of waste Visual pollution Low fuel costs More traffic More jobs for local people

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