1. PHYSICS 2 FORCES IN MOTION & ELECTRICITY AND THE ATOM

2. FORCES IN MOTION

3. Velocity & Acceleration Speed is how fast you’re going with no regard to the distance eg 30mph or 20m/s. Velocity is how fast you’re going in a certain direction eg 15mph north or 46m/s 060°. Acceleration is how quickly your speeding up and how quickly the velocity is changing eg 0.84m/s². speed(m/s)= _________ distance(m) time(s) acceleration(m/s²) = _________ change in velocity(m/s) time taken(s)

4. DT & VT Graphs Distance Time Graphs gradient = speed flat sections are where it’s stopped steeper the graph the faster it’s going downhill sections mean it’s going backwards to the start a steepening curve means its accelerating a leveling off curve means its decelerating Velocity Time Graphs gradient = acceleration flat sections represent steady speed steeper the graph the greater the acceleration or deceleration uphill sections are acceleration downhill sections are deceleration the area under any section of the graph or all of it is equal to the distance traveled in that time interval curve means changing acceleration

5. Mass Weight & Gravity Gravity is the force of attraction between all masses gravity attracts all masses on the surface of a planet, it makes all things accelerate towards the ground it gives everything weight it keeps planets, moons and satellites in their orbits, the orbit is a balance between the forward motion of the object and the force of gravity pulling it inwards Weight & Mass mass is the amount of stuff in an object weight is caused by the pull of gravity an object has the same mass anywhere in the universe but its weight will vary depending on the force of gravity weight is a force measured in newtons using a spring balance of newton meter mass is not a force and is measured in kilograms using a mass balance weight(n) = mass(kg) x gravitational field strength(n/kg)

6. Laws of Motion First Law An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force. in the absence of an unbalanced force, objects will keep on doing what they’re doing objects resist changes in their state of motion Second Law Acceleration is produced when a force acts on a mass. The greater the mass of the object being accelerated the greater the amount of force needed to accelerate the object. heavier objects require more force to move the same distance as lighter objects overall unbalanced force is often called the resultant force an unbalanced force will always produce acceleration or deceleration it can take 5 different forms: starting, stopping, speeding up, slowing down, changing direction resultant force(n) = mass(kg) x acceleration(m/s²) Third Law For every action there is an equal and opposite re action. every force there is a reaction force that is equal in size but opposite in direction when you push an object it pushes you back

7. Drag & Terminal Velocity Friction is Always There to Slow Thing Down if an object has no force pushing it along it will always slow down and stop because of friction. friction always acts in the opposite direction to movement to travel at a steady speed, the driving force needs to balance to frictional forces you get friction between two surfaces in contact Drag Increases as the Speed Increases resistance or drag is caused when an object passes through air or a liquid to reduce drag the shape of the object should be streamlined like boats, fishes parachute and bird wings have high drag the resistance increases with speed Terminal Velocity is the Maximum Speed When falling objects first set off they fall faster and faster as their weight is much bigger than the resistance. As his speed increases the resistance increases so the acceleration gradually decreases. The resistance force will eventually equal to the acceleration force and it won’t be able to accelerate any more. This is its maximum speed which is called the terminal velocity.

8. Stopping Distance The stopping distance of a car is the distance covered in the time between the driver first spotting a hazard and the coming to a complete stop. The distance it takes to stop a card is divided into the thinking distance and the breaking distance. Thinking Distance The distance the car travels in the split second between the driver noticing the hazard and applying the brakes. It is affected by: how fast your going: whatever your reaction time, the faster you’re going the further you’ll go how fast your reaction is: this is affected by tiredness, drugs, alcohol, age, careless attitude Braking Distance The distance the car travels during its deceleration whilst the brakes are being applied. It is affected by: how fast your going: faster, the further it takes to stop how heavy the vehicle: a heavy loaded vehicle takes longer to stop how good the brakes are: all brakes must be checked and maintained regularly, worn or faulty will let you down massively when you need them the most how good the grip is: depends on road surface, weather conditions and tires, the more grip the more friction

9. Work Done work done(j) = force(n) x distance(m) Work Done is Energy Transferred when something moves, something else is providing some sort of effort to move it the thing putting effort in needs a supply of energy it then does work by moving the object and it transfers the energy it receives whether this energy is transferred usefully or is wasted it is still worked done and it measured in joules

10. Kinetic & Potential Energy kinetic energy(j) = ½ x mass(kg) x velocity(m/s) 2 Kinetic Energy is Energy of Movement anything which is moving has kinetic energy the kinetic energy of something depends on its mass and speed the greater its mass and the faster it’s going, the bigger its kinetic energy will be Energy Can Be Stored as Potential Energy elastic potential energy: is the energy when work is done on an elastic object to change its shape, this is released as kinetic energy when the object springs back into shape gravitational potential energy: is the energy stored in an object when you raise it to a height against gravity, you have to move something to increase its gravitational potential energy and that energy is only released when the movement falls

11. Momentum & Collisions momentum(kgm/s) = mass(kg) x velocity(m/s) Momentum it is how difficult an object is to stop greater the mass of an object and greater its velocity, the more momentum the object has momentum is a vector quantity, it has size and direction before momentum equals after momentum it is conserved in any collisions or explosions when no external forces act if one object loses momentum, the other object must of gained the same amount lost Forces Cause Changes In Momentum force(n) = ___________________________ when a force acts on an object it causes a change in momentum larger force means a faster change in momentum and so greater acceleration increasing the time decreases the force: crumple zones, seat belts, airbags change in momentum(kgm/s) time taken(s)

12. ELECTRICITY & THE ATOM

13. Static Electricity Static Is Caused By Friction when two insulating materials are rubbed together, electrons will transfer from one onto the other this will leave a positive electric charge on one and a negative electric charge on the other, which way the electrons transfer depend on the materials electrically charged objects will attract small objects placed near them as they want to give or take electrons from them to become neutral with polythene rod electrons move from the duster to the rod and with the acetate rod electrons move from the rod to the duster a charged object can be discharged safely by connecting it to the earth with a metal strap, the electrons flow down the strap to the ground if the charge is negative or flow up the strap from the ground if the charge is positive Charges like charges repel, opposite charges attract, if one is charged and the other is not they attract forces get weaker the further apart the two things are greater the charge on an isolated object, the greater the voltage between it and the earth, if the voltage gets big enough there’s a spark which jumps across the gap

14. Static Electricity Being Helpful smoke precipitators: smoke particles reach the bottoms of the chimney they meet a wire grid with a high negative charge which charges the smoke negatively, they are attracted to positively charged metal plates and they stick together to form larger particles, when heavy enough they fall off the plates or are knocked off, the dust falls to the bottoms of the chimney and can be removed photocopier: the image plate is positively charges and an image of what you’re photocopying is projected onto it, whiter bits of the thing you’re copying make light fall on the plate and the charge leaks away in those places, the charged bits attract negatively charged powder which is transferred onto positively charged paper, the paper is heated so the powder sticks Being Dangerous: lighting: rain drops and ice bump together inside storm clouds, knocking off electrons and leaving the top of the cloud positively charges and the bottom of the cloud negative, this creates a huge voltage and a big spark grain chutes, paper rollers, fuel filling: as fuel flows out of a filler pipe, paper drags over rollers or grain shoots out of pipes static can build up and this can lead to a spark and in dusty fumy places will blow up

15. Circuits current is the flow of electrons round the circuit, it will only flow through a component if there is a voltage across that component, measured in ampere (A) voltage is the driving force that pushes the current around, measured in volt (V) resistance is anything in the circuit which slows down the flow, measured in ohm (Ω) If you increase the voltage, the more current will flow. If you increase the resistance, the less current will flow or more voltage will be needed to keep the same current flowing. Standard Test Circuit: The Ammeter measures the current in amps flowing through the component must be placed in series can be put anywhere in series in the main circuit The Voltmeter measures the voltage in volts across the component must be placed in parallel around the component proper name for voltage is potential difference

16. Resistance resistance (R) = _________________ Different Resistors the current through a resistor is proportional to voltage different resistors have different resistance therefore have different slopes Filament Lamp as the temperature of the filament increase, the resistance increase so creating the curve Diode current will only flow through a diode in one direction potential difference (V) current (I)

17. Circuit Devices Variable Resistor a resistor whose resistance changes by turning a knob they alter the current flowing through a circuit: turn the resistance up the current drops and turn the resistance down the current goes up Diode device made from semiconductor material like silicon lets current flow in one direction but not in the other as there’s a very high resistance in the reverse direction LDR (light dependent resistor) in bright light the resistance falls and in darkness the resistance is highest this makes it a useful device for things like night lights and burglar detectors Thermistor (temperature dependent resistor in hot conditions the resistance drops and in cool conditions the resistance goes up makes useful temperature detectors for car engines and electronic thermostat

18. Series Circuits Potential Difference is Shared the total voltage of the supply is shared between various components, so the voltages round a series circuit add up to equal the source voltage Current is the Same Everywhere the same current flows through all parts of the circuit the size of the current is determined by the potential difference of the cells and the total resistance of the circuit Resistance Adds Up the total resistance is the sum of all the resistances bigger the resistance of a component, the bigger its share of the total potential difference Series Circuits – All or Nothing the different components are connected in a line, end to end between the +ve and –ve of the power supply if you remove or disconnect one component, the circuit is broken and they all stop

19. Parallel Circuits Parallel Circuits – Independence & Isolation each component is separately connected to the +ve and – ve of the supply if you remove or disconnect one of them, it will hardly effect the others at all you have to switch everything on and off separately Potential Difference is the Same Across All Components all the components get the full source of potential difference so the voltage is the same across all components Current is Shared Between Branches total current flowing around the circuit is equal to the total of all the currents in the separate branches there are junctions where the current either splits of rejoins, the total current going in a junction has to equal the total current leaving Resistance is Tricky the current through each component depends on its resistance, lower the resistance bigger the current that’ll flow through it total resistance is always less that that of the branch with the smallest resistance

20. Mains Electricity Main Supply is AC, Battery Supply is DC UK mains supply is about 230volts it is an AC supply (alternating current) which means the current is constantly changing direction the frequency of the AC mains supply is 50Hz cells and batteries supply DC (direct current) which means that the current keeps flowing in the same direction Oscilloscope a cathode ray oscilloscope (CRO) is a voltmeter if you plug in a source you get a trace on the screen that shows how the voltage of the supply changes with time vertical height of the trace at any point shows the input voltage at that point DC Supply a DC source is always at the same voltage, so you get a straight line AC Supply an AC source gives a regularly repeating wave you can work out the period and the frequency of the supply frequency(Hz)= _________ 1 Time Period (s)

21. Mains Electricity Hazards in the Home long cables frayed cables cables in contact with something hot or wet water near sockets shoving things into sockets damaged plugs too many plugs into 1 socket lighting sockets without bulbs in appliances without their covers on Plugs & Cables Wiring the right coloured wire to each pin and firmly screwed in no bare wires showing inside the plug cable grip tightly fastened over the cable outer layer Features metal parts are made of copper or brass as they are very good conductors case, cable grip and cable insulator are all made of plastic or rubber as these are really good insulators and are flexible too this all keeps the electricity flowing where is should

22. Fuses & Earthing Main Cables have 3 Separate Wires live wire is a mains supply alternates between a high +ve and –ve voltage neutral wire is always at 0v electricity normally flows in and out through the live an neutral wires only earth wire is just for safety, it works together with a fuse to prevent fire and shocks Fuses Prevent Electric Shocks fuses prevent surges of current in electric circuits and danger of electrical shocks if the current in the circuit gets bigger than the fuse rating, the fuse wire heats up and the fuse blows, breaking the circuit and preventing any electric shocks fuses should be rated as near as possible but just higher than the normal operating current Earthing Prevents Fires & Shocks the earth pin is connected to the case through the earth wire if a fault develops in which the live somehow touches the metal case, then because the case is earthed, a big current flows through the live through the case and out down the earth wire this surge in current blows the fuse, which cuts off the live supply this prevents electric shocks from the case

23. Energy & Power Energy is transformed from cells and other sources anything which supplies electricity is also supplying energy so cells, batteries, generators all transform energy to components in the circuit – motion: motors, light: light bulbs, heat: kettles, sound: speakers Resistors produce heat when a current flows through them whenever a current flows through anything with electrical resistance (which is everything) the electrical energy is converted into heat energy the more current that flows, the more heat is produced a bigger voltage means more heating because it pushes more current through you can measure the amount of heat produced by putting a resistor in a known amount of water or inside a solid block and measuring the increase in temperature Energy(j) = Power(w) x Time(s) Power(w) = Voltage(V) x Current(A)

24. Charge & Energy Change Total Charge(C) = Current(A) x Time(s) When current flows past a point in a circuit for a length of time then the charge that has passed can be worked out. More charge passes around the circuit when a bigger current flows. Voltage is the energy transferred per charge passed when an electrical charge goes through a change in voltage then energy is transferred energy is supplied to the charge at the power source to raise it through a voltage the charge gives up this energy when it falls through any voltage drop in components elsewhere in the circuit the bigger the change in voltage the more energy is transferred for a given amount of charge passing through the circuit Energy Transferred(j) = Charge(C) x Potential Difference(V)

25. Atomic Structure the nucleus is in the middle and is tiny, it contains protons and neutrons electrons move around the nucleus giving the atoms its overall size ParticleMassCharge Proton1+1 Neutron10 Electron1/2000 Isotopes are Different Form of the Same Element the atomic number of an element is the total number of protons in one atom of it, the mass number is the total number of protons and neutrons in one atom isotopes are atoms with the same number of protons but a different number of neutrons, so they have the same atomic number but a different mass number unstable isotopes are radioactive, which means they decay into other elements and give out radiation this is where all radioactivity comes from, unstable radioactive isotopes undergoing nuclear decay and spitting out high energy particles

26. Radioactive Decay Alpha Particles an alpha particle is a helium nucleus, mass 4 and charge or +2 made up off 2 protons and 2 neutrons they are relatively big, heavy and slow moving don’t penetrate very far into materials but are stopped quickly there size makes them strong ionising, which means they bash into a lot of atoms and knock electrons off them before they slow down which creates lots of ions Beta Particles a beta particle is an electron with virtually no mass and a charge or -1 they move quite fast, are quite small they penetrate moderately before colliding and are moderately ionising a neutron in the nucleus is converted to a proton and electron, the electron is emitted as a beta particle and the number of protons in the nucleus increases by one Gamma Rays a gamma rays are very short wavelength with no mass and no charge they penetrate a long way into materials without being stopped they are weakly ionising as they tend to pass through rather than colliding with atoms, eventually they hit something and do damage after an alpha or beta emission the nucleus sometimes has extra energy to get rid of, it does this by emitting a gamma ray, they never change the proton or mass numbers of the nucleus

27. Background Radiation Background radiation we receive comes from: radioactivity of naturally occurring unstable isotopes which are all around us radiation from space which is known as cosmic rays, mostly from the sun radiation because of human activity like fallout from nucleus explosions, dumped nuclear waste – this is a tiny portion Level of Background Radiation the level of background radiation changes depending on where you are at high altitudes it increases because of more exposure to cosmic rays underground mines it increases because of the rocks all around certain underground rock like granite can cause higher levels at the surface especially if they release radioactive radon gas which tends to get trapped inside people’s houses Radon Gas the radon concentration is people’s houses varies widely across the UK depending on what type of rock the house it built on exposure to high doses of radon gas can cause lung cancer, greater the exposure higher the risk there is a debate on the effects of lower doses and what the highest safe concentration is medical professionals reckon that about 1 in 20 deaths from lung cancer are cause by radon exposure new houses in areas where high levels of radon gas might occur must be designed with good ventilation systems, these reduce the concentration of radon in the living space

28. Nuclear Fission Nuclear Fission – Splitting Up of Big Atomic Nuclei nuclear power stations and nuclear submarines are both powered by nuclear reactors in a nuclear reactor a controlled chain reaction takes place in which atomic nuclei split up and release energy in the form of heat this heat is used to heat water to drive a steam turbine the fuel that’s split is usually either uranium 235 or plutonium 239 Chain Reactions: 1) a neutron hits a uranium or plutonium nucleus and the nucleus splits 2) as it splits it releases energy and two or three neutrons 3) these neutrons might hit another nucleus causing it to split and so on keeping the chain reaction going when a large atoms splits in two it will form two new lighter elements, these new nuclei are usually radioactive as they have the wrong number of neutrons in them nuclear power produces huge amounts of radioactive material which is very difficult and expensive to dispose of safely each nucleus splitting (fission) gives out a lot of energy, nuclear processes release much more energy than chemical processes, that’s why nuclear bombs are much more powerful

29. Nuclear Fusion Nuclear Fusion – Joining of Small Atomic Nuclei two light nuclei (eg hydrogen) can combine to create a larger nucleus, is called nuclear fusion fusion releases a lot of energy, all the energy released in stars comes from fusion so people are trying to develop fusion reactors to make electricity fusion doesn’t leave a lot of radioactive waste and there’s plenty of hydrogen to use as fuel the problem is that fusion can only happen at really high temperatures about 10million°c no material can stand thay temperature without being vapourised, so fusion reactors are hard to build at the moment experimental reactors are not generating electricity and are taking more power to get up to temperature than the reactor can produce