11/03/2016 Physics 2 11/03/2016 Distance, Speed and Time Speed = distance (in metres) time (in seconds) D TS 1)Seb walks 200 metres in 40 seconds. What.

11/03/2016 Physics 2

11/03/2016 Distance, Speed and Time Speed = distance (in metres) time (in seconds) D TS 1)Seb walks 200 metres in 40 seconds. What is his speed? 2) Lucy covers 2km in 1,000 seconds. What is her speed? 3) How long would it take Freddie to run 100 metres if he runs at 10m/s? 4) Sue travels at 50m/s for 20s. How far does he go? 5) Hannah drives her car at 85mph (about 40m/s). How long does it take her to drive 20km? 50 m/s 2km = 2000 m  2 m/s 10 m/s 1000 m 500 s

11/03/2016 Distance-time graphs 40 30 20 10 0 20 40 60 80100 4) Diagonal line downwards = 3) Steeper diagonal line = 1)Diagonal line = 2) Horizontal line = Distance (metres) Time/s Steady speed Stationary Faster steady speed Steady speed in other direction

11/03/2016 40 30 20 10 0 20 40 60 80100 1)What is the speed during the first 20 seconds? 2)How far is the object from the start after 60 seconds? 3)What is the speed during the last 40 seconds? 4)When was the object travelling the fastest? Distance (metres) Time/s 0.5 m/s 40 m 1 m/s 40 – 60 s

11/03/2016 Speed vs. Velocity Speed is simply how fast you are travelling… Velocity is “speed in a given direction”… This car is travelling at a speed of 20m/s This car is travelling at a velocity of 20m/s east

11/03/2016Acceleration V-U TA Acceleration = change in velocity (in m/s) (in m/s 2 ) time taken (in s) 1)A cyclist accelerates from 0 to 10m/s in 5 seconds. What is her acceleration? 2)A ball is dropped and accelerates downwards at a rate of 10m/s 2 for 12 seconds. How much will the ball’s velocity increase by? 3)A car accelerates from 10 to 20m/s with an acceleration of 2m/s 2. How long did this take? 4)A rocket accelerates from 1,000m/s to 5,000m/s in 2 seconds. What is its acceleration? 2 m/s 2 120 m/s 5 s 2000 m/s 2

11/03/2016 Velocity-time graphs 80 60 40 20 0 10 20 30 4050 Velocity m/s T/s 1) Upwards line = 2) Horizontal line = 3) Upwards line = 4) Downward line = acceleration Steady speed slower acceleration deceleration

11/03/2016 80 60 40 20 0 1)How fast was the object going after 10 seconds? 2)What is the acceleration from 20 to 30 seconds? 3)What was the deceleration from 30 to 50s? 4)How far did the object travel altogether? 10 20 30 4050 Velocity m/s T/s 40 m/s 10 m/s 2 1 m/s 2 6700 m

11/03/2016 Balanced and unbalanced forces Consider a camel standing on a road. What forces are acting on it? Weight Reaction These two forces would be equal – we say that they are BALANCED. The camel doesn’t move anywhere.

11/03/2016 Balanced and unbalanced forces What would happen if we took the road away? Weight Reaction

11/03/2016 Balanced and unbalanced forces What would happen if we took the road away? The camel’s weight is no longer balanced by anything, so the camel falls downwards… Weight

11/03/2016 What would happen if we took the road away? The camel’s weight is no longer balanced by anything, so the camel falls downwards… Balanced and unbalanced forces

11/03/2016 Air Resistance Air resistance is a force that opposes motion through air. The quicker you travel, the bigger the air resistance: The same applies to a body falling through a liquid (called “drag” or “upthrust”).

11/03/2016 Balanced and unbalanced forces Forward movement Acceleration Constant speed or stopped Backwards movement

11/03/2016 Balanced and unbalanced forces 1) This animal is either ________ or moving with _____ _____… 4) This animal is… 2) This animal is getting _________… 3) This animal is getting _______…. stopped steady speed faster slower dead

11/03/2016 Resultant Force Calculate the resultant force of the following: 500N100N700N600N 700N 200N 800N 100N 50N 400N to the right 100N to the right 200N up 50N up

11/03/2016 Force and acceleration If the forces acting on an object are unbalanced then the object will accelerate, like these wrestlers: Force (in N) = Mass (in kg) x Acceleration (in m/s 2 ) F AM

11/03/2016 Force, mass and acceleration 1)A force of 1000N is applied to push a mass of 500kg. How quickly does it accelerate? 2)A force of 3000N acts on a car to make it accelerate by 1.5m/s 2. How heavy is the car? 3)A car accelerates at a rate of 5m/s 2. If it weighs 500kg how much driving force is the engine applying? 4)A force of 10N is applied by a boy while lifting a 20kg mass. How much does it accelerate by? F AM 2 m/s 2 2000kg 2500N 0.5m/s 2

11/03/2016 Terminal Velocity Consider a skydiver: 1)At the start of his jump the air resistance is _______ so he _____________ downwards. 2) As his speed increases his air resistance will _______ 3) Eventually the air resistance will be big enough to _______ the skydiver’s weight. At this point the forces are balanced so his speed becomes ________ - this is called TERMINAL VELOCITY Words – increase, small, constant, balance, accelerates small accelerates increase balance constant

11/03/2016 Terminal Velocity Consider a skydiver: 4) When he opens his parachute the air resistance suddenly ________, causing him to start _____ ____. 5) Because he is slowing down his air resistance will _______ again until it balances his _________. The skydiver has now reached a new, lower ________ _______. Words – slowing down, decrease, increases, terminal velocity, weight increases slowing down decrease weight terminal velocity

11/03/2016 Velocity-time graph for terminal velocity… Velocity Time Speed increases… Terminal velocity reached… Parachute opens – diver slows down New, lower terminal velocity reached Diver hits the ground On the Moon

11/03/2016 Weight vs. Mass Earth’s Gravitational Field Strength is 10N/kg. In other words, a 1kg mass is pulled downwards by a force of 10N. W gM Weight = Mass x Gravitational Field Strength (in N) (in kg) (in N/kg) 1)What is the weight on Earth of a book with mass 2kg? 2)What is the weight on Earth of an apple with mass 100g? 3)Dave weighs 700N. What is his mass? 4)On the moon the gravitational field strength is 1.6N/kg. What will Dave weigh if he stands on the moon? 20N 1N 70kg 112N

11/03/2016 Stopping a car… Braking distance Too much alcohol Thinking distance (reaction time) Tiredness Too many drugs Wet roads Driving too fast Tyres/brakes worn out Icy roads Poor visibility

11/03/2016 Work done When any object is moved around work will need to be done on it to get it to move (obviously). We can work out the amount of work done in moving an object using the formula: Work done = Force x distance moved in J in N in m W DF

11/03/2016 Example questions 1.Bori pushes a book 5m along the table with a force of 5N. He gets tired and decides to call it a day. How much work did he do? 2.Alicia lifts a laptop 2m into the air with a force of 10N. How much work does she do? 3.Martin does 200J of work by pushing a wheelbarrow with a force of 50N. How far did he push it? 4.Chris cuddles his cat and lifts it 3m in the air. If he did 75J of work how much force did he use? 5.Carl drives his car 1000m. If the engine was producing a driving force of 2000N how much work did the car do? 25J 20J 4 m 25N 200000J

11/03/2016 Elastic Potential Energy Elastic potential energy is the energy stored in a system when work is done to change its shape, e.g: a spring, a bungee cord

11/03/2016 Kinetic energy Any object that moves will have kinetic energy. The amount of kinetic energy an object has can be found using the formula: Kinetic energy = ½ x mass x velocity squared in J in kg in m/s KE = ½ mv 2

11/03/2016 Example questions 1)Nicole drives her car at a speed of 30m/s. If the combined mass of her and the car is 1000kg what is her kinetic energy? 2)Shanie rides her bike at a speed of 10m/s. If the combined mass of Shanie and her bike is 80kg what is her kinetic energy? 450000J 4000J

11/03/2016Momentum Any object that has both mass and velocity has MOMENTUM. Momentum (symbol “p”) is simply given by the formula: Momentum = Mass x Velocity (in kg m/s) (in kg) (in m/s) P VM What is the momentum of the following? 1)A 1kg football travelling at 10m/s 2)A 1000kg Ford Capri travelling at 30m/s 3)A 20g pen being thrown across the room at 5m/s 4)A 70kg bungi-jumper falling at 40m/s 0.1 kg m/s 33.3 m/s 0.1 m/s 2800 m/s

11/03/2016 Conservation of Momentum In any collision or explosion momentum is conserved (provided that there are no external forces have an effect). Example question: Two cars are racing around the M25. Car A collides with the back of car B and the cars stick together. What speed do they move at after the collision? Mass = 1000kgMass = 800kg Speed = 50m/sSpeed = 20m/s Momentum before = momentum after… …so 1000 x 50 + 800 x 20 = 1800 x V… …V = 36.7m/s Mass = 1800kg Speed = ??m/s

11/03/2016 Momentum in different directions What happens if the bodies are moving in opposite directions? Speed = 50m/s Mass = 1000kg Speed = 20m/s Mass = 800kg Momentum is a VECTOR quantity, so the momentum of the second car is negative… Total momentum = 1000 x 50 – 800 x 20 = 34000 kg m/s Speed after collision = 34000 kg m/s / 1800 = 18.9m/s

11/03/2016 Random questions… 1)Sophie tries to run 100m in 12 seconds and succeeds. How fast did she run? 2)Tommy accelerates at a rate of 2m/s 2 for 3 seconds. If he started at 10m/s what was his final speed? 3)Charlie decides to lift his book up into the air. His book has a mass of 100g and he lifts it 50cm. Calculate the work done. 4)Lewis accelerates from 0 to 10m/s in 5 seconds. If his mass is 70kg how much force did his legs apply? 5)Rachel rides 1km at a speed of 20m/s. How long did the journey take? 6)Claire thinks it’s funny to push James with a force of 120N. If James has a mass of 60kg calculate his acceleration. 7)Lauren brakes do 20,000J of work. If the combined mass is 100kg what speed was she travelling at? 8)Tom has a mass of 75kg. If he accelerates from 10 to 20m/s in 2s how much force did he apply? 8.3 m/s 16 m/s 1g = 0.01N0.5J 140N 50s 2 m/s 2 375N

11/03/2016 9)Georgina amuses herself by throwing things at Sarah. If she throws a ball with a speed of 20m/s and the distance between her and Sarah is 5m how long will it take to reach her? 10)Mr Richards throws calculators around the room with a force of 20N. If each calculator has a mass of 200g calculate the acceleration. 11)Sam has a mass of 70kg. What is his weight on Earth, where the gravitational field strength is 10N/kg? 12)Zak pushes a box around with a force of 1N. He does 5J of work and decides to call it a day. How far did he push it? 13)On the moon Matt might weigh 112N. If the gravitational field strength on the moon is 1.6N/kg what is his mass? What will he weigh on Earth? 14)Dan likes bird watching. He sees a bird fly 100m in 20s. How fast was it flying? 15)How much kinetic energy would Richard have if he travelled at a speed of 5m/s and has a mass of 70kg? 0.25s 100 m/s 2 700N 5m 70kg 700N 5 m/s 875J

11/03/2016 Static Electricity Static electricity is when charge “builds up” on an object and then stays “static”. How the charge builds up depends on what materials are used: + - + - + + - - - + + + - - + + + - - -

11/03/2016 Static Electricity + + + - - - - - - - - -

11/03/2016 Van de Graaf generators

11/03/2016 Uses of Static – Smoke Precipitators - - - - - - + + + Chimney Negatively charged plates Positively charged grid

11/03/2016 Circuit Symbols VA Battery Cell Fuse Resistor LDR Voltmeter Ammeter Variable resistor Diode Switch Bulb Thermistor

11/03/2016 Electric Current Electric current is a flow of negatively charged particles (i.e. electrons). Note that electrons go from negative to positive -+ e-e- e-e- By definition, current is “the rate of flow of charge”

11/03/2016 Basic ideas… Electric current is when electrons start to flow around a circuit. We use an _________ to measure it and it is measured in ____. Potential difference (also called _______) is how big the push on the electrons is. We use a ________ to measure it and it is measured in ______, a unit named after Volta. Resistance is anything that resists an electric current. It is measured in _____. Words: volts, amps, ohms, voltage, ammeter, voltmeter ammeter amps voltage voltmeter volts

11/03/2016 More basic ideas… If a battery is added the current will ________ because there is a greater _____ on the electrons If a bulb is added the current will _______ because there is greater ________ in the circuit increase push decrease resistance

11/03/2016 Current in a series circuit If the current here is 2 amps… The current here will be… And the current here will be… In other words, the current in a series circuit is THE SAME at any point 2A

11/03/2016 Current in a parallel circuit A PARALLEL circuit is one where the current has a “choice of routes” Here comes the current… And the rest will go down here… Half of the current will go down here (assuming the bulbs are the same)…

11/03/2016 Current in a parallel circuit If the current here is 6 amps The current here will be… And the current here will be… 2A 6A

11/03/2016 Some example questions… 3A6A 1A 3A 1.5A

11/03/2016 Voltage in a series circuit V VV If the voltage across the battery is 6V… …and these bulbs are all identical… …what will the voltage across each bulb be? 2V

11/03/2016 Voltage in a series circuit V V If the voltage across the battery is 6V… …what will the voltage across two bulbs be? 4V

11/03/2016 Voltage in a parallel circuit If the voltage across the batteries is 4V… What is the voltage here? And here? VV 4V

11/03/2016Summary In a SERIES circuit: Current is THE SAME at any point Voltage SPLITS UP over each component In a PARALLEL circuit: Current SPLITS UP down each “strand” Voltage is THE SAME across each”strand”

11/03/2016 An example question: V1V1 V2V2 6V 3A A1A1 A2A2 V3V3 A3A3 1.5A £A 6V 3V

11/03/2016 Georg Simon Ohm 1789-1854Resistance Resistance is anything that will RESIST a current. It is measured in Ohms, a unit named after me. The resistance of a component can be calculated using Ohm’s Law: Resistance = Voltage (in V) (in  )Current (in A) V RI

11/03/2016 An example question: V A 1)What is the resistance across this bulb? 2)Assuming all the bulbs are the same what is the total resistance in this circuit? 15Ω Voltmeter reads 10V Ammeter reads 2A 5Ω5Ω

11/03/2016 More examples… 12V 3A 6V 4V 2A 1A 2V What is the resistance of these bulbs? 4Ω4Ω 2Ω2Ω 2Ω2Ω

11/03/2016Resistance Resistance is anything that opposes an electric current. Resistance (Ohms,  ) = Potential Difference (volts, V) Current (amps, A) What is the resistance of the following: 1)A bulb with a voltage of 3V and a current of 1A. 2)A resistor with a voltage of 12V and a current of 3A 3)A diode with a voltage of 240V and a current of 40A 4)A thermistor with a current of 0.5A and a voltage of 10V 3Ω3Ω 4Ω4Ω 6Ω6Ω 20Ω

11/03/2016 Resistors, bulbs and diodes

11/03/2016 Current-voltage graphs I V I V I V 1. Resistor 3. Diode 2. Bulb Current increases in proportion to voltage As voltage increases the bulb gets hotter and resistance increases A diode only lets current go in one direction – it has very high resistance in the other direction

11/03/2016 LDRs and Thermistors

11/03/2016 Two simple components: 2) Thermistor – resistance DECREASES when temperature INCREASES 1) Light dependant resistor – resistance DECREASES when light intensity INCREASES Resistance Amount of light Resistance Temperature

11/03/2016 Wiring a plug Earth wire Neutral wire Insulation Live wire Fuse 1. 2. 3. 4. 5. 6. Cable grip The live wire of a plug alternates between positive and negative potential relative to the Earth The neutral wire of a plug stays at a potential close to zero relative to the Earth

11/03/2016 DC and AC DC stands for “Direct Current” – the current only flows in one direction: AC stands for “Alternating Current” – the current changes direction 50 times every second (frequency = 50Hz) 1/50 th s 230V V V Time T

11/03/2016Fuses Fuses are _______ devices. If there is a fault in an appliance which causes the ____ and neutral (or earth) wire to cross then a ______ current will flow through the _____ and cause it to _____. This will break the _______ and protect the appliance and user from further _____. Words – large, harm, safety, melt, live, circuit, fuse safety live large fuse melt circuit harm

11/03/2016 Power and fuses Power is “the rate of doing work”. The amount of power being used in an electrical circuit is given by: P IV Power = voltage x current in W in V in A Using this equation we can work out the fuse rating for any appliance. For example, a 3000W fire plugged into a 240V supply would need a current of _______ A, so a _______ amp fuse would be used (fuse values are usually 3, 5 or 13A). 12.513

11/03/2016 Power and fuses Copy and complete the following table: AppliancePower rating (W) Voltage (V)Current needed (A) Fuse needed (3, 5 or 13A) Toaster960240 Fire2000240 Hairdryer300240 Hoover1000240 Computer100240 Stereo80240 45 8.313 1.253 4.25 0.423 0.333

11/03/2016 Energy and Power The POWER RATING of an appliance is simply how much energy it uses every second. In other words, 1 Watt = 1 Joule per second E TP E = Energy (in joules) P = Power (in watts) T = Time (in seconds)

11/03/2016 Earth wires Earth wires are always used if an appliance has a _____ case. If there is a _____ in the appliance, causing the live wire to ______ the case, the current “_______” down the earth wire and the ______ blows. Words – fuse, fault, metal, surges, touch metal fault touchsurges fuse

11/03/2016 Structure of the atom 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:

11/03/2016 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 – atom is made up of a small, positively charged nucleus surrounded by electrons orbiting in a “cloud”.

11/03/2016 The structure of the atom ELECTRON – negative, mass nearly nothing PROTON – positive, same mass as neutron (“1”) NEUTRON – neutral, same mass as proton (“1”)

11/03/2016 The structure of the atom ParticleRelative MassRelative Charge Proton1+1 Neutron10 Electron0 MASS NUMBER = number of protons + number of neutrons SYMBOL PROTON NUMBER = number of protons (obviously)

11/03/2016Isotopes 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. Notice that the mass number is different. How many neutrons does each isotope have? A “radioisotope” is simply an isotope that is radioactive – e.g. carbon 14, which is used in carbon dating.

11/03/2016 Background Radiation Radon gas Food Cosmic rays Gamma rays Medical Nuclear power 13% are man-made

11/03/2016 Types of radiation 1) Alpha (  ) – an atom decays into a new atom and emits an alpha particle (2 protons and 2 _________ – the nucleus of a ______ atom) 2) Beta (  ) – an atom decays into a new atom by changing a neutron into a _______ and electron. The fast moving, high energy electron is called a _____ particle. 3) Gamma – after  or  decay surplus ______ is sometimes emitted. This is called gamma radiation and has a very high ___________ with short wavelength. The atom is not changed. Unstable nucleus New nucleus Alpha particle Beta particle Gamma radiation Words – frequency, proton, energy, neutrons, helium, beta neutrons helium proton beta energy frequency

11/03/2016 Nuclear fission Uranium or plutonium nucleus Unstable nucleus New nuclei (e.g. barium and krypton) More neutrons Neutron

11/03/2016 Chain reactions Each fission reaction releases neutrons that are used in further reactions.

11/03/2016 Nuclear Fusion in stars ProtonNeutron

11/03/2016 Physics 2 11/03/2016 Distance, Speed and Time Speed = distance (in metres) time (in seconds) D TS 1)Seb walks 200 metres in 40 seconds. What.

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11/03/2016 Physics 2 11/03/2016 Distance, Speed and Time Speed = distance (in metres) time (in seconds) D TS 1)Seb walks 200 metres in 40 seconds. What.

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