Physics Revision  Motion  Forces  Work, energy and momentum  Current electricity  Main electricity  Radioactivity  Energy from the nucleus

Motion: Distance-time graphs ) Diagonal line downwards = Speed 3) Steeper diagonal line = Speed (Faster than in 1) as the gradient is steeper 1)Diagonal line = Speed 2) Horizontal line = Stationary Distance (metres) Time/s

Motion: Velocity-time graphs Velocity m/s Time (s) 1) Upwards line = acceleration 2) Horizontal line = no acceleration 3) Upwards line = acceleration 4) Downward line = deceleration

Motion

Forces Forces can change an objects:  Speed  Shape  Direction Force measured in Newtons (N) Balanced forces:  Objects stays still  Constant speed Unbalanced forces:  Speed changes  Direction changes

Forces Resultant force  single force that has the same effect as all the forces acting on an object Zero resultant force  Object stays still or constant Non zero resultant force  velocity changes Resultant force (N) = Mass (Kg) x Acceleration (m/s 2 )

Forces Stopping distance = thinking distance braking distance Factors affecting stopping distance:  Tiredness  Drugs/Alcohol  Wet/Icy roads  Speed  Distraction – phone/people

Forces Weight  Force of gravity acting on it  Measured in Newtons (N) Mass  Amount of matter an object has  Measured in Kg

Forces Terminal velocity  Accelerates downwards because of its weight  There is a resultant force acting downwards  Gains speed, the air resistance on it increases.  Object's weight is balanced by the air resistance.  There is no resultant force  Object reaches a steady speed (terminal velocity)

Work, Energy and Momentum  Work done = amount of energy transferred  Work done depends on amount of force and distance moved  Power = rate of energy transfer  Measured in watts

Work, Energy and Momentum Gravitational Potential Energy (GPE)  Higher up = more GPE Kinetic Energy (KE)  Depends on mass and speed

Work, Energy and Momentum Momentum  Unit = kg m/s  Total momentum before = total momentum after Explosions  move with different speeds if mass unequal  Move with equal and opposite momentum Car safety  Crumple zone – increase impact time, reduce force  Air bags - increase impact time, reduce force

Current Electricity Static electricity  Objects become charged  Electrons are transferred  Materials that become positive lose electrons  Materials that become negative gain electrons  Opposite charges attract

Current Electricity Electric Current  Flow of charge  Electrons transfer energy  More electrons that pass through more current  Charge measured in coulombs (C) Q

Current Electricity  E = work done (j)  V = Potential difference (v)  Q = Charge (C)  V = Potential difference (v)  I = Current (a)  R = Resistance (Ω)

Current Electricity  Ammeter connected in series  Voltmeter connected in parallel Ohm’s law  Current through resistor at constant temperature is directly proportional to P.D across the resistor

Current electricity Current directly proportional to P.D Resistance increases as temperature increases Resistance higher in reverse direction

Current electricity - Series Circuit  The current is the same in each component  Potential differences of all components added together equals the total P.D of the circuit  Adding the resistances gives total resistance of resistors in series

Current electricity - Parallel circuit  Current through each component added together equals the total current through the circuit  Potential difference is the same across each component  The bigger the resistance of a component the smaller the current

Mains Electricity Direct current (DC)  Current travels in one direction  Example – simple circuit Alternating current (AC)  Current repeatedly reverses its direction  Frequency = number of waves per second (Hz)  Oscilloscope measures the waves

Circuit electricity – Plugs  Fuses are a safety measure  If the current gets too high the fuse melts  This breaks the circuit stopping the current flowing  Prevents electrical fires

Mains Electricity Power  Energy transferred each second  Measured in watts Choosing a fuse  Electrical power/P.D  Choose the fuse nearest to the current through the device  3A, 5A or 13A

Radioactivity ELECTRON – negative, mass nearly nothing PROTON – positive, same mass as neutron (“1”) NEUTRON – neutral, same mass as proton (“1”)

Radioactivity Radioactive substance contains unstable nuclei, become stable by emitting radiation  Alpha – 2 protons, 2 neutrons  Beta – An electron  Gamma – Electromagnetic wave Ionisation  radiation can cause atoms to become charged  Can damage or kill living cells  Can cause damage to genes

Radioactivity A hundred years ago people thought that the atom looked like a “plum pudding” – a sphere of positive charge with negatively charged electrons spread through it… I did an experiment (with my colleagues Geiger and Marsden) that proved this idea was wrong. I called it the “Scattering Experiment” Ernest Rutherford, British scientist:

Radioactivity: The Rutherford Scattering Experiment Alpha particles (positive charge, part of helium atom) Thin gold foil Most particles passed through, 1/8000 were deflected by more than 90 0 Conclusion – the atom is made up of a small, positively charged nucleus surrounded by electrons orbiting in a “cloud”.

Radioactivity An isotope is an atom with a different number of neutrons: Each isotope has 8 protons – if it didn’t then it just wouldn’t be oxygen any more. A “radioisotope” is simply an isotope that is radioactive – e.g. carbon 14, which is used in carbon dating.

Radioactivity RadiationRange in air Ionising Power Can pass through paper? Can pass through 5mm of Aluminium? Can pass through 5cm of Lead? Magnetic field deflection Alpha α 5cm Highly Ionising No Deflected towards negative plate Beta ß 15cmIonisingYesNo Deflected toward positive plate Gamma ƴ Much further Weakly ionising Yes Almost all of it is stopped, but some gets through None

Radioactivity Radon gas Food Cosmic rays Gamma rays Medical Nuclear power 13% are man-made Background radiation

Radioactivity Half life  Average time for the number of nuclei of the isotope to half  Geiger counter used to measure activity

Radioactivity Beta – Metal foil  Use beta to test the thickness of foil  If thickness too much the beta readings drop Gamma – Radioactive tracers  Used to test kidney function  Radiation can be detected outside the body  Use isotope with a short half life Carbon dating  Tests the age of wood and organic materials

Energy from nucleus - Fission  Uranium 235 isotope or Plutonium 239 isotope  Nucleus of the atom splits  Releases lots of energy  2 or 3 neutrons released  Chain reaction – neutrons hit into other atoms and causes them to split  Generates massive amounts of heat  Produces dangerous nuclear waste

Energy from nucleus - Fusion  Joining of 2 nuclei to form a larger nucleus  Typically Hydrogen atoms join to make Helium atoms  Energy released when they join  Nuclear fusion releases energy in the sun  No radioactive waste made  Needs very high temperatures which is difficult to control  Hydrogen is easily available for use

Life cycle of a star Protostar – dust and clouds that form a star Red giant – Expanded then cooled making it red, larger and cooler than before White dwarf – A collapsed star after red giant stage, hotter and denser than before Black dwarf – A faded out star that has gone cold Supernova – Explosion of a massive star after fusion has stopped Black hole – Object that has so much mass nothing can escape not even light

Energy from nucleus Early universe  A galaxy is a collection of billions of stars held together by gravity  Force of gravity pulled matter (hydrogen and helium) into galaxies and stars How the elements formed  Light elements are formed inside stars from fusion (H, He, C)  Heavier elements are formed in supernova as well as light ones  The sun and the solar system were formed from debris of a supernova

Units Speed/Velocity – m/s Distance – meters (m) Acceleration – m/s 2 Force – Newton (n) Mass – Kilograms (Kg) G.F.S – N/Kg Energy – Joules (J) Power – Watts (w) Current – Amps (a) Charge – Coulombs (C) Potential difference – Volts (v) Resistance – Ohms (Ω) Frequency – Hertz (Hz)