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# Physics Unit P2

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Revison for AQA Physics P2. With pictures to help remember

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### Physics Unit P2

1. 1. Physics 2
2. 2. DistanceDistance-Time Graphs• Gradient = Speed• Flat sections are stationary• Straight = steady speed• Curves= acceleration ordeceleration
3. 3. Velocity and AccelerationAcceleration is how quickly velocity is changingAcceleration=Change in Velocity/Time TakenVelocity-Time Graphs• Gradient = Acceleration• Flat sections = steady speed• Area under the graphrepresents distance• Curve is change inacceleration
4. 4. Weight• MASS is the “stuff” inside, whereas WEIGHT isthe force due to gravity• Weight = Mass x Gravitational Field Strength• Earths GFS is 10N/Kg
5. 5. Resultant Forces• It is the overall FORCE• The overall effect of forces which will decidethe motion of an object• If two forces are acting in the samedirection, the resultant force is the sum ofthose two• If two forces are acting along the sameline, then the resultant force is found bysubtracting them
6. 6. Driving force=1000NPushing Force=600NResultant Force=1600NDriving force=1000NFriction=600NResultant Force=400N
7. 7. Acceleration• If the resultant force in 0 the object isstationary• It there is no resultant force on a movingobject, then it will carry on moving withconstant velocity• If there is an resultant force, then the objectwill accelerate in the directionof the force• That is until the force equal outagain
8. 8. • Force = Mass x AccelerationOr Acceleration = Force / Mass• When two object interact, the forces they put(exert) upon each other are equal andopposite• This is called a reaction force, so if you pushagainst something it will push back againstyou with equal force
9. 9. Friction• It acts against movement• If you travel at a steady speed, the drivingforce needs to equal the frictional force• Streamlining reduces drag or air resistance• Drag increases as speed increases, as youaccelerate you hit more air particles withmore force. This created more drag
10. 10. Terminal Velocity• When an object first falls, gravity (weight) hasmore force than frictional forces• This causes the object to acceleratedownwards• As the speed increases, so does the drag• This reduces the acceleration• Weight can not get any bigger,so you reach terminal velocity(fall at a steady speed)
11. 11. Stopping DistanceThinking Distance• Faster you are going = Further you will go• Your Reactions- Tiredness, drugs, alcohol, badvisibility and distractionsBraking Distance• Faster you are going = Further you will go• The Car- the condition of Tyres and condition ofBrakes• The Road- road surface and weather condition
12. 12. 30 mph50 mph70 mph9m15m21m14m38m75mSo this shows thatthinking distance isdirectionally proportionalbut braking distance issquarely proportionalThinking BrakingDistance DistanceStopping Dis. = Thinking Dis. + Braking Dis.
13. 13. Work Done• To move an object energy has to betransferred• The energy can be used usefully i.e. To movesomething or wastefully i.e. Friction• Work Done= Force x Distance Moved
14. 14. Gravitational Potential Energy• When an object is lifted vertically work is doneagainst the force of gravity. This is transferredinto gravitational potential energy (GPE)• GPE= Mass x Height x GFS (gravitational field strength)• The Earth has a GFS of 10N/Kg
15. 15. Kinetic Energy• Any thing that moves has kinetic energy• Kinetic Energy = ½ Mass x Speed²• Moving car has lots of KE so to slow it downenergy is lost i.e. Heat energy• Work done = KEF x d = ½ mv²• Falling objects have the potential energy lost andthey gain kinetic energy
16. 16. Elasticity• Apply a force = Stretch the Object• Work done is stored as ELASTIC POTENTIALENERGY• Then its goes back to its original shapereleasing the energy as KINETIC ENERGY
17. 17. • Extension of Spring is DIRECTIONALLYPROPORTIONAL to the force applied• Force = K (spring constant) x energy• There is a limit to a springs elasticity, it isnormal until it reaches its maximum force• Past this point the spring will notreturn to its original shape
18. 18. Power• It is the rate of doing work• Power = Work Done / Time Taken• Measured in Watts, which means 1 Watt is 1joule of energy transferred every second
19. 19. Momentum• It’s a property of a moving object• Momentum = Mass x Velocity• Also P before = P after• Momentum is a vector, so has direction• When a force acts upon an object it changesits momentum• The bigger the force the faster the change ofmomentum
20. 20. Car Safety• Brakes transform the kinetic energy of the carinto thermal energy on the road• Regenerative brakes don’t transform into heatthe transform into electrical energy• Big change in Momentum in a short time =MASSIVE
21. 21. END OF FIRST HALF
22. 22. Static Electricity• It is created when two object rub against eachother and either lose or gain electrons• Like charges repel, so if hair had been chargedthen the hair would separate because theirlike charges repel each other• However these charges can beeasily lost through a conductor
23. 23. Current and Voltage• Current is the rate of flow of charge• Current= Charge / Time• The Potential Difference is the work done percoulomb of charge• Voltage = Work Done / Charge
24. 24. Circuits
25. 25. ResistanceCurrent through aresistor (at constanttemp.) is directionallyproportional toVoltageThe higher the resistancethe higher thepotential differenceHowever in a normalfilament lamp thetemperature of thefilament increasesthis causes the curveThis is a Diode. Thecurrent will only flowin one direction. Thediode has a very highresistance in theopposite direction
26. 26. Series• All or nothing, if one component breaks aodoes the circuit• Potential difference is shared out, so in 23fairy-lights on the mains electricity they allhave a voltage of 10V• Current is the same everywhere• And the Resistance builds/adds up, 5 bulbswith 10Ω so the circuit has 50Ω
27. 27. Parallel• Things can be switched off separately• Voltage is the same across all components• However current is shared between eachbranch. The current going in is the same asgoing out, but the components have differentcurrents going across them
28. 28. Mains Electricity• Supplied in AC• Has 230V• And has frequency of 50Hz• It can be shown on an oscilloscope
29. 29. Electricity in the HomeHazards: Long Cables; Frayed cables; damagedplugs; too many plugs in 1 socket; water nearsocketsThe wires: Live wire carries the alternatingcurrent; Neutral has 0V and Earth is attachedto metal casing
30. 30. BLUEEFTBROWNIGHT
31. 31. Fuses and Earthing• Fault in the LIVE WIRE causes it to touch themetal case• This causes a larger current to flow throughthe circuit• This surge cause the FUSE to MELT• This cuts of the live supply and breaks thecircuit, THUS saving the appliance and theuser
32. 32. Live wire touchesthe metal casingBig Surge of Electricityto earthFault in the LiveWireThe Fuse melts/blows The appliance is SAFE
33. 33. Energy and Power• All resistors produce heat when a currentflows through them. The more current themore heat• To be energy efficient they have to transfermore of their total electrical energy to a usefulsource• Energy Transferred= Power Rating x Time
34. 34. Atomic Structure- Rutherford• In 1909 Rutherford fired alpha particles at goldfoil to discover more about particles• He found most went straight through, this showsparticles are mostly empty space• Some came straight back, the shows that most ofthe mass is concentration in a central nucleus• Some were deflected, this shows thenucleus is positive and there must benegative electrons not in the nucleus
35. 35. Radiation• Isotopes are atoms of the same element but areslightly different, they have the same number ofprotons but different numbers of neutrons• Radioactivity is entirely random, it comes from anunstable and decaying nuclei. This emits alpha,beta or gamma radiation• Background radiation comes from: naturallyunstable isotopes like rocks and food;space like cosmic rays; Man-madeplaces like weapons and medicine andpower-stations
36. 36. Types of RadiationAlpha radiation is a helium nucleus, so two protonsand two neutrons. Can’t penetrate much butbecause of its size it’s strongly ionising (bash intoatoms and knock electrons off of them)Beta radiation is an electron which is emitted whena neutron turns into a proton. Can go throughsome things and is mildly ionisingGamma radiation is an ray. This penetrateseverything but is weakly ionising.
37. 37. Radiation Safety• Radiation damage depend on the type of radiation andhow long you were exposed• Alpha particles are deflected slightly by magnetic fieldbut beta particles are extremely deflected by themagnetic field• Granite release radon gas which can be trapped inpeoples houses• Nuclear industry workers wear protective clothing andface masks and have radiation badges• Radiographers work behind lead screens and wear leadaprons
38. 38. Half-Life• Half life is the AVERAGE TIME it takes for theNUMBER OF NUCLEI in a radioactive isotopeto HALVE• Radioactivity never stops, there will always besome activity, so its hard to measure• Short half life means lots of nuclei decayquickly, activity falls quickly
39. 39. -1 Half Life- -1 Half Life- -1 Half Life-
40. 40. Uses of Radiation• Smoke detectors- alpha particles make and circuitand smoke breaks the circuit, making the alarmgo off• Sterilisation- Gamma rays are used to kill bacteriaon food or medical equipment, without harmingthem• Radiotherapy- gamma is fired at a cancer to kill allof those cells, but damage is done• Tracers- beta or gamma sources areput into someone and an externaldetector says where most of theradiation is
41. 41. Damage of Radioactivity• Large amounts of radiation kill cells and leave youwith radiation sickness, but nothing else• Small amounts cause minor damage to cellswithout killing them. They then mutant anddivide uncontrollably, this is a cancer• Alpha is very harmful inside the body because itdamages a very localised area• Beta and gamma are dangerous outside the bodybecause they can penetrate the skin
42. 42. Nuclear Fission• This is what happens in nuclear power stationsand nuclear bombs• An Neutron had to be absorbed by anunstable nuclei• This creates two new smaller nuclei andreleases more neutron, this makes a chainreaction• This gives out a lot of energy
43. 43. Nuclear Fusion• This is where two small nuclei join to create alarger nucleus and energy• Fusion doesn’t leave a lot of radioactive wasteand there is a bounty of fuel (hydrogen)• It can only happen at really high temperatures• You need at strong magnetic force to hold thepressure and heat21H H11+ 32He + ENERGY
44. 44. Life Cycle of StarsNebula- Thenursery for Stars.Clouds of Dust andgas start to form.Gravity makes itspiral and form aProtostarProtostar- Gravityis turned into heat.The temp is thenhigh enough fornucleur fusion tostart. This givesout light, starMain Sequencestar- long stableperiod whereoutward pressure isequal to the force ofgravity (the sun) butthis can’t lastforeverRed Giant-hydrogen hasrun out and itwas a small starRed SuperGiant-Hydrogen hasrun out but itwas a big starOR
45. 45. Red GiantRed Giant- small star makethis. It is unstable so ejectsits outer layer of dust andgas.White Dwarf- This is what’sleft after the red giant. It isa hot solid, dense core.When it cools down itbecomes a Black DwarfPlanetary Nebula- This is theouter layer of duct and gas.
46. 46. Red SuperGiantRed SuperGiant- Thisis made from largestars. They glow morebrightly because theydo more fusion, sothey expandSupernova- This is theexplosion of the RedSuperGiant. It formselements heavier thaniron and spreads themout into the universecreating new planetsand new starsNeutron Star-What is left ofthe supernovais a dense core.This is anneutron starORBlack Hole- Ifthe star is bigenough theremains of thesupernova willform a blackhole