P2 Physics Resultant forces forces act in pairs, opposite directions resultant force = difference between 2 forces If equal and opposite = balanced = no movement OR move at constant speed if not equal = unbalanced = movement in direction of bigger force Graphs DT graph = speed. Steeper the gradient = faster Velocity is speed in a direction VT graph = acceleration Steeper the gradient = greater acceleration Area under graph = distance travelled Stopping distance Thinking distance affected by tiredness, drugs & alcohol – PERSON Braking distance affected by road conditions, weather, brakes – CAR & ENVIRONMENT Terminal velocity 2 forces act on falling objects – weight (gravity) & air resistance 5 stages during parachute jump A – weight greater than air resistance = increase in speed B – air resistance increases but weight still bigger = start to slow down C – weight = air resistance = steady speed = terminal velocity D - parachute opens, increase in surface area, air resistance greater than weight = decrease in speed E – weight = air resistance = steady speed = lower terminal velocity Hooke’s law Elastic objects return to original shape Extension is directly proportional to force applied force = spring constant x extension too much extension – object won’t return to original shape. Reached limit of proportionality (P) Force (N) = mass (kg) x acceleration (m/s 2 ) Speed(m/s) = distance(m)/time (s) Acceleration (m/s 2 ) = change in velocity (m/s) / time (s) Stopping distance = thinking + braking distance Work done (J) = force (N) x distance (m) Power (W) = energy (J) / time (s) Energy work done = energy transferred friction in the form of heat power is energy transferred in a given time gravitational potential energy is due to height. GFS = 10 N/kg kinetic energy depends on mass and speed GPE (J) = mass (kg) x gravitational field strength (N/kg) x height (m) Kinetic energy (J) = ½ x mass (kg) x velocity (m/s) Momentum the product of the mass and velocity of the object, has size & direction conserved in any collision car safety features reduce the forces due to a large change in momentum > seat belts > crumple zones > air bags the time over which the change in momentum happens increases, so less impact from forces

Static electricity Gain negative electrons = negatively charged lose negative electrons = positively charged like charges = repel, opposite charges attract used in photocopiers & smoke precipitators can be dangerous – petrol stations Circuits negative electrons flow from the negative terminal current – ammeter – in series current = flow of electric charge voltage/ potential difference – voltmeter – in parallel potential difference = driving force that pushes current series = one loop parallel = more than one loop resistance = anything that slows current resistance varies in different components resistance in a LDR decreases as LI increases resistance in a thermistor decreases as LI increases Current (A) = charge (C) / time (s) Resistance (Ω) = voltage (V) / current (A) Houeshold electricity a.c = alternating current – mains supply d.c = direct current – batteries frequency = number of waves per second = hertz. UK supply = 50 Hz UK 3 pin plugs  Brown = live, Blue = neutral, Green & yellow = earth Two-core cable = no earth wire, appliance has casing made of insulator and no metal parts Fuses contain a piece of wire - if the current is too high, the fuse wire will melt and break the circuit. Circuit breakers detect a surge in current – open a switch and break circuit. Faster than fuses, but more expensive than fuses. Residual current circuit breaker (RCCB) detects difference between live and neutral wires and cuts off power. Normally exactly the same current flows through the live and neutral wires Oscilloscope traces Used to determine the time period & frequency of a supply frequency (Hz) = 1 / time period (s) time period = distance between 2 peaks time period = timebase x number of divisions Atom structure protons mass = 1, charge = +1 electrons mass = 0, charge -1 neutrons mass = 1, charge = 0 mass number = protons + neutrons atomic number = protons OR electrons Power (W) = energy transferred (J) / time (s) Charge (C) = current (A) x time (s) Energy transferred (J) = potential difference (V) x charge (C) ISOTOPES atoms of the same element with different numbers of neutrons

Atoms & radiation background radiation comes different source radiation dose depends on dose and occupation Radioactive decay Totally random process Unaffected by physical conditions 3 types: 1)Alpha decay – unstable nucleus emits an alpha particle (He nucleus) Mass # decrease by 4, atomic # decrease by 2. 2) Beta decay - unstable nucleus changes a neutron into a proton and emits an electron. Mass # unchanged, atomic # increases by one. 3)Gamma decay – short wavelength electromagnetic radiation given off. Alpha and beta particles are deflected by electric and magnetic fields – in opposite directions due to opposite charges Half-life the average time it takes for the number of nuclei of a radioactive isotope in a sample to halve.. Rutherford & Marsden Rutherford & Marsden fired alpha particles at gold foil. Most particles passed straight through the foil. Some particles were deflected slightly. Some were rebounded back towards the source CONCLUSION - all atoms consist largely of empty space with a small, dense positive core that he called the nucleus and around this nucleus the negative electrons were spaced out. Led to a change in model from plum pudding to nuclear Nuclear fission splitting of atomic nuclei happens in nuclear power stations chain reaction – a slow moving neutron is absorbed by a uranium or plutonium nucleus. The nucleus splits – releasing more neutrons which can then hit other nuclei and cause them to split and so on and so on …… Nuclear fusion 2 lighter nuclei join together to make a larger nucleus. fusion releases a lot of energy no radioactive waste like fission BUT only happens at really high temperatures – difficult to hold hydrogen at high temps and pressures