13.1 How can we describe the way things move? Speed (m/s) = distance (m) /time (s) Distance- time graph Steeper the line – greater the speed

Velocity = speed in a stated direction Velocity-time graph Acceleration(m/s 2 ) = change in velocity(m/s)/time(s) The steeper the slope the greater the acceleration. A horizontal line indicates a constant speed The area underneath a velocity-time graph represents the distance travelled

13.2 How do we make things speed up or slow down? Force = push or pull (N) Forces are balanced – object stationary or constant speed. Resultant force = zero Forces are unbalanced – object will move, speed up, slow down or change direction. Resultant force = difference in direction of bigger one Force (N) = mass (kg) x acceleration (m/s 2 ) Stopping distance = braking + thinking distance Braking affected by road, weather & vehicle conditions Thinking affected by tiredness, drugs & alcohol Falling objects – air resistance (up) & weight (down) weight (N) = mass (kg) x G.F.S (N/kg) [10n/kg] Terminal velocity – maximum speed of falling object

13.3 What happens to the movement energy when things speed up or slow down? Work done [energy] (J) = force (N) x distance in direction (m) If there is friction, energy converted into heat energy Kinetic energy(J) = ½ x mass(kg) x speed 2 ((m/s) 2 )

13.4 What is momentum? Momentum(kg m/s) = mass(kg) x velocity(m/s) has both magnitude and direction Momentum is conserved in any collision or explosion. Force(N) = change in momentum (kg m/s)/ time(s) Vehicles use momentum for safety features Seat belts increases the time taken for the body’s momentum to reach zero, and so reduces the forces on it. Air bags increase the time taken for the head’s momentum to reach zero, and so reduces the forces on it.

13.5 What is static electricity, how can it be used and what is the connection between static electricity & electric currents? Rub insulating materials together they become charged Gain electrons = negatively charged Lose electrons = positively charged Like charges = repel Opposite charges = attract Charges move through conductors, not through insulators Charges are used in photocopiers and smoke precipitators Photocopiers – image copied to + charged plate. – charged toner attracted to image, fixed in place by heat. Smoke precipitators – smoke particles pass through charged grid become + charged. Particles attracted to – flow of electricity = current Charged conductor discharged by connecting to Earth Static can be dangerous - petrol stations. Turn off the engine, don’t use mobile phones. - refuelling planes. Tanker & plane linked by copper conductor

13.6 What does the current through an electrical circuit depend on? Current (A) – ammeter connected in series Potential difference (V) – voltmeter connected in parallel Current in series circuit always the same, p.d splits up, total resistance = resistance of components Current in parallel circuit splits up, p.d always the same Resistance = how hard it is for current to flow, measured in ohms (Ω) Resistance(Ω) = potential difference (V) / current (A) LDR Ω decreases as light intensity increases Thermistor Ω decreases as the temperature increases

13.7 What is mains electricity and how can it be used safely? d.c flows in the same direction. Cells and batteries use d.c a.c changes direction continuously. Mains supply is a.c frequency = number of complete cycles of reversal per seconds UK frequency = 50Hz, p.d = V Neutral carries the current away Live carries the current to appliance Earth wire & fuse – safety Fuse breaks circuit is current too big Fuse used should be slightly higher than current device needs: Wires are copper = a good conductor, surrounded by flexible plastic which is a good insulator Pins made from brass - good conductor Oscilloscope trace - Frequency (Hz) = 1 / time period (s) Time period = horizontal distance between peaks - time period of the signal in divisions. Multiply the number of divisions by the timebase per division

13.8 Why do we need to know the power of electrical appliances? Current = flow of charge (A) Charge flows through resistor electrical energy -> heat energy Power = rate of energy transformed Power (W) = energy transferred (J) / time (s) Power (W) = current (A) x voltage (V) Amount of charge in a circuit is measured in coulombs (C) Charge (C) = current (A) x time (s) Greater the p.d the more energy transformed per coulomb Energy transformed (J) = potential difference (V) x charge (C)

13.9 What happens to radioactive substances when they decay? Mass number = protons + neutrons, atomic number = protons Isotope = same # of protons, different # of neutrons Atoms that gain or lose e- are ions Radioactive isotopes = atoms with unstable nuclei that decay Alpha decay – alpha particle emitted. Mass number decrease by 4, atomic number decreases by 2 Beta decay – neutron -> proton + electron emitted. Mass number stays same, atomic number increases by 1 Ionisation - radioactive particles collide with neutral atoms -> become charged as electrons knocked out Background radiation = naturally occurring. No threat, comes from atmospheric gases, medical, nuclear industry, cosmic rays, gamma rays from rocks, soil & building materials and from food Rutherford & Marsden fired alpha particles at gold foil. Some went through, some deflected, some rebounded. Model changed from “plum pudding” to nuclear atomic model. ParticleMassCharge Proton1+1 Neutron10 ElectronAlmost 0

13.10 What are nuclear fission & nuclear fusion? Nuclear fusion = joining of atomic nuclei. Forms a larger atomic nucleus & releases more energy than needed - self sustaining. How stars release energy. Nuclear fission = splitting of atomic nuclei. Used in nuclear reactors to produce energy to make electricity. Uranium 235 & Plutonium fissionable substances Nucleus absorbs a neutron -> nucleus unstable. Splits into two smaller nuclei and additional neutrons. Energy is also released. Neutrons can go on to start a chain reaction.