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Slide 2 P4 P5 P6 Revision P4 Explaining Motion P5 Electric Circuits P6 Radioactive materials Slide 3 P4 Explaining Motion Slide 4 speed (m/s) = distance travelled (m) / time taken (s) Usually when an object travels from A to B its velocity will vary so a calculation of its velocity is really an average velocity. An instantaneous velocity is the velocity at a given moment. Distances measured in one direction are positive, and in the other, negative. A negative velocity means moving in the opposite direction. Slide 5 10 9 8 7 6 5 4 3 2 1 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Time (s) D i s t a n c e (m) 1. What is the velocity of the object at first ? 2. For how long was the object stationary ? 3. What is the velocity in the last part ? 9 3 = 3 m/s 6 s 9 6 = - 1.5 m/s Slide 6 1. A ball is thrown and takes 4 seconds for its velocity to steadily increase to 4 m/s and then travels at a constant velocity for 5 seconds. It then hits a wall and rebounds at a constant velocity of 3 m/s for 5 s before it is caught. 5 4 3 2 1 0 -2 -3 -4 -5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Velocity (m/s) Time (s) Slide 7 2. An object moves at a velocity of 2 m/s for 3 seconds and then accelerates at 1 m/s 2 for 2 seconds. It then moves at a constant velocity for 3 seconds and then decelerates at 1 m/s 2 until it is stationary. It remains stationary for 2 seconds and then accelerates backwards at 2 m/s 2 for 1 second. It then takes 2 seconds to steadily decelerate till it stops. 5 4 3 2 1 0 -2 -3 -4 -5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 V e l o c i t y (m/s) Time (s) Slide 8 8 m A car is travelling at 30 km/hr Will she survive ? The driver has a reaction time of 1 second 30 km = 30,000 m 1 hr = 3,600 s In 1 second the car would travel 30,000 3,600 = 8.33 m The woman is hit BEFORE the driver applies the brakes !!!! X A woman walks out onto the road Slide 9 For a distance-time graph a steeper gradient means a higher speed distance time steeper gradient - faster A tachometer continuously measures an objects speed and can be used to make a tachograph. Slide 10 If the speed of an object is increasing, we say that it is accelerating. Acceleration (m/s2) = change of velocity, m/s time taken for the change (s) Slide 11 A force arises from an interaction between two objects. When one object exerts a force on another, it always experiences a force in return (a reaction force). A force and a reaction force are called an interaction pair. The two forces in an interaction pair are equal in size and opposite in direction and they act on different objects. box the box acts downwards on the table due to gravity the table acts upwards on the box due to the reaction force the two forces are equal and opposite Slide 12 gravity reaction force of the ground acting on the feet force of the feet acting on the ground reaction force of friction on acting on the feet Walking Slide 13 The horizontal motion of objects (like cars and bicycles) can be analysed in terms of a driving force (produced by the engine or the cyclist), and a counter force (due to friction and air resistance). driving force greater than counter force speeding up driving force equal to counter force stationary driving force less than counter force slowing down A resultant force takes into account all the acting forces. 50N 30N resultant force = 20N 20 N Slide 14 Friction is the interaction between two surfaces when they slide over each other Friction is caused by the roughness of the sliding surfaces There is a friction force on both objects involved Friction enables cars and people to get moving Slide 15 momentum (kg m/s) = mass (kg) velocity (m/s) If a resultant force acts on an object, it causes a change of momentum in the direction of the force A car has a mass of 5,000 kg and a velocity of 4 m/s. What is the cars momentum ? 5,000 x 4 = 20,000 kg m/s A cyclist cycling at 10 m/s has a momentum of 540 kg m/s. The cyclist has a mass of 50 kg, whats the mass of the bike ? total mass = 540 / 10 = 54 kg mass of bike = 54 50 = 4 kg If a resultant force on an object is zero then there is no change of momentum if it is stationary, it stays at rest if it is already moving, it continues at a steady speed in a straight line eg when the driving force = friction Slide 16 m1m1 m2m2 Total momentum before = total momentum afterwards m 1 = m 2 v 1 = -v 2 momentum after = m 1 v 1 + m 2 v 2 = -m 1 v 1 + m 2 v 2 = 0 momentum before = m 1 v 1 + m 2 v 2 = m 1 v 1 + -m 2 v 2 = 0 positive momentum = to the rightnegative momentum = to the left Slide 17 m1m1 m2m2 m 1 = m 2 v 2 = 0 momentum before = m 1 v 1 + m 2 v 2 = m 1 v 1 + 0 = m 1 v 1 momentum after = m 1 v 1 + m 2 v 2 = 0 + m 2 v 2 = m 2 v 2 therefore m 1 v 1 = m 2 v 2 ie all the momentum of the first ball is transferred to the second ball Slide 18 m1m1 m2m2 m 2 > m 1 v 2 = 0 momentum before = m 1 v 1 + m 2 v 2 = m 1 v 1 + 0 = m 1 v 1 momentum after = m 1 v 1 + m 2 v 2 = -m 1 v 1 + m 2 v 2 m 1 rebounds of m 2 and transfers some of its momentum to m 2 Slide 19 m1m1 m2m2 m 2 pushes off m 1 v 2 = 0 momentum before = m 1 v 1 + m 2 v 2 = 0 + 0 = 0 v 1 = 0 m 1 > m 2 momentum after = m 1 v 1 + m 2 v 2 = -m 1 v 1 + m 2 v 2 therefore m 1 v 1 = m 2 v 2 Slide 20 change of momentum = resultant force x time during which it acts When a force is applied to an object, its velocity increases The longer the force is applied, the greater the change in velocity momentum= mass x When a force is applied to an object, its momentum increases velocity The longer the force is applied, the greater the change in momentum The greater the force applied, the greater the change in velocity The greater the force applied, the greater the change in momentum increasing the velocity increases momentum Slide 21 change of momentum = resultant force x time for which it acts Increasing the time it takes for a change in momentum reduces the force that causes the change in momentum If the time from impact to the velocity becoming zero is increased then the impact force is reduced which means less injury Seat belts, air bags, crumple zones, cycle helmets etc increase the time during impact and therefore reduce the impact force. crumple zone Slide 22 The energy of a moving object is called kinetic energy When a force moves an object, work is done work done (J) = force (N) distance moved (m) A braking force of 1000N is applied by a driver to stop his car. The car covered 50m before it stopped. How much work did the brakes do ? 1,000 x 50 = 50,000 J Slide 23 As an object falls, its gravitational potential energy decreases as it is transferred into kinetic energy and heat (friction with the air) When an object is lifted to a higher position above the ground, work is done by the lifting force against the gravitational force acting on the object (its weight) Slide 24 When an object is lifted this increases the objects gravitational potential energy (GPE) change in GPE (J) = weight (N) height difference (m) A crane is lifting a 50kg load up into the air with a constant speed. If the load is raised by 20m how much work has the crane done ? remember that 1 kg has a weight of 10 N (on Earth) 50 kg = 500 N work done = 500 x 20 = 10,000 J Slide 25 kinetic energy (J) = mass (kg) [velocity] 2 (m/s 2 ) A 70 kg boy runs at 10m/s. What is his kinetic energy ? kinetic energy = x 70 x 10 2 = x 70 x 100 = 3,500 J What is the kinetic energy of a 100g tennis ball being thrown at a speed of 5m/s ? 100g = 0.1 kg kinetic energy = x 0.1 x 5 2 = x 0.1 x 25 = 1.25 J E = m v 2 Slide 26 A parachutist with a total mass of 70 kg jumps from a helicopter at a height of 1,500 m. He pulls the cord of the parachute when he is 1,000 m above the ground. (a) Ignoring air resistance, what is the speed of the parachutist just as he pulls the cord ? E = m v 2 You will need to use the formula E = m v 2. You are given the mass (70kg) in the question and you can work out E (energy) by using GPE = weight x height. Remember that 70kg = 700N. GPE = 700 x (1,500 1,000) = 700 x 500 = 350,000 J GPE = weight x difference in height 350,000 = m v 2 700,000 = m v 2 700,000 = 70 x v 2 700,000 / 70 = v 2 v 2 = 10,000 v = 10,000 v = 100 m/s {replacing E with 350,000} {multiplied both sides by 2} {replacing m with 70} {divided both sides by 70} {getting the square root} Slide 27 (b) Why doesnt the parachutist actually reach the speed calculated in part (a) ? [2 marks] because of air resistance [1], some of the gravitational potential energy is dissipated as heat [1] (c) The parachutist actually reached the velocity of 40 m/s before the using the parachute. How much energy was dissipated ? total energy = 350,000 J velocity (without taking air resistance into account) = 100 m/s velocity (taking air resistance into account) = 40 m/s = 40% therefore 60% of the energy is dissipated 350,000 x 60 / 100 = 21,000 J (d) What principle is used to calculate part (c) ? the conservation of energy (all of the energy is accounted for) Slide 28 {B to C = steady speed and C to D = fastest speed} Slide 29 1.65 hrs gradient / slope 144 112 = 32 4.0 2.7 = 1.3 speed = 32 / 1.3 = 24.6 m/s 24.6 m/s Lance Slide 30 outlier / anomoly /anomalous (38 + 41 + 40 + 37) / 4 = 39 Slide 31 Slide 32 kinetic energy = m v 2 1875 Slide 33 no change / nothing / stays the same Slide 34 P4 Explaining Motion P5 Electric Circuits P6 The Wave Model of Radiation Slide 35 P5 Electric Circuits Slide 36 Electric charge objects become charged when electrons are transferred to or from them, for example, by rubbing Two types of charge are positive and negative (these names are just labels) Two objects with the same charge repel each other Two objects with different charges attract each other Slide 37 + metal ions electrons The electrons experience resistance when they flow through the metal. The potential difference (voltage) provides energy which makes the electrons move through the metal ie it generates a current. potential difference The symbol for voltage is V The symbol for current is I The symbol for resistance is R Metal wire Normally the free electrons in a metal move around slowly at random. current voltage resistance Slide 38 V v1v1 v2v2 I i1i1 i2i2 I = i 1 = i 2 The current is the same everywhere V = v 1 + v 2 SERIES The sum of the voltages across each component equals the supply voltage R= r1r1 + r2r2 Resistance Slide 39 I i1i1 i2i2 PARALLEL Current I3I3 i4i4 i5i5 I = I 3 I 1 = I 4 I 2 = I 5 I = I 1 + I 2 Current does not get used up Total current = the sum of the currents through each component Slide 40 V v1v1 v2v2 V = v 1 = v 2 The voltage across each component is the same as the supply voltage. PARALLEL Voltage = energy per unit of charge Slide 41 If more bulbs are added in parallel to a circuit then they will all be as bright as normal and more current is drawn from the power supply The potential difference is largest across the component with the greatest resistance, because more energy is transferred by the charge flowing through a large resistance than through a small one The current is smallest through the component with the largest resistance, because the same battery voltage causes more current through a smaller resistance than a bigger one Slide 42 12 V 4 V5 V 2A i3i3 SERIES v3v3 1 ohm3 ohmr3r3 i 3 = 2 Av 3 = 3 Vr 3 = 2 ohm Slide 43 12 V v2v2 PARALLEL 1 A i3i3 4 A r3r3 i 3 = 2 A v 2 = 12 V 12 ohm Slide 44 Current is a flow of electrons Electrons have charge (negative) So current is a flow of charge How do we quantify current ? Current is the amount of charge flowing in a particular amount of time Slide 45 Voltage provides energy to the electrons Electrons have charge (negative) So Voltage provides energy to the charge How do we quantify voltage ? Voltage is the amount of energy a particular amount of charge has Slide 46 What about resistance ? All components will offer resistance to a flow of electrons How do we quantify resistance ? If a current of 1A flows through a component when the voltage across it is 1V then the component is said to have a resistance of 1 ohm [ 1 Slide 47 I V R = Multiply both sides by R I V R = R xx R R I = VOr V = I R Take V = I R and divide both sides by I V I R II = V I =R or V I =R Slide 48 I V R = V = I R V I =R V IR Q. A current of 4 A flows through a circuit with resistance 3 WW hat is the voltage ? use V = I R V = 4 x 3Voltage = 12 current = voltage / resistancevoltage = current x resistanceresistance = voltage / current V Slide 49 Q. A current of 5 A flows through a circuit with voltage 10 V WW hat is the resistance ? V IR V I =R use R = 10 5 resistance = 2 Q. A circuit with voltage of 6 V h h as a resistance of 2 . What current should flow ? use V R =I I = 6 2 current = 3 A Slide 50 Q. A current of 4 A flows through a circuit with voltage 12 V WW hat is the resistance ? V IR V I =R use R = 12 4 resistance = 3 Q. A circuit with voltage of 8 V h h as a resistance of 2 . What current should flow ? use V R =I I = 8 2 current = 4 A Q. A current of 60 A flows through a circuit with resistance 4 WW hat is the voltage ? use V = I R V = 60 x 4Voltage = 240V I V R = V = I R V I =R Slide 51 Q. A current of 2 A flows through a circuit with voltage 16 V WW hat is the resistance ? V IR V I =R use R = 16 2 resistance = 8 Q. A circuit with voltage of 230 V h h as a resistance of 5 . What current should flow ? use V R =I I = 230 5 current = 46 A Q. A current of 25 A flows through a circuit with resistance 3 WW hat is the voltage ? use V = I R V = 25 x 3Voltage = 75V I V R = V = I R V I =R Slide 52 The higher the temperature the lower the resistance The greater the light intensity the lower the resistance Slide 53 Variable resistors Resistors are used in circuits to control the size of the current Two resistors in series have a larger resistance than one on its own. Connecting two resistors in parallel makes a smaller total resistance Two resistors in series make a potential divider Slide 54 Voltage (V) Current (A) Current through a filament bulb Current is less here due to the extra resistance of the heating effect Slide 55 Power = current X voltage (watt,W) (ampere, A) (volt, V) If you know the power, it is easy to calculate how much work is done (or how much energy is transferred) in a given period of time: Work done (or energy transferred) = power x time (joule, J) (watt, W) (second, s) Slide 56 AC generator DC generator The size of the induced voltage can be increased by: increasing the speed of rotation of the magnet or electromagnet or coil; increasing the strength of its magnetic field; increasing the number of turns on the coil; placing an iron core inside the coil Generators produce a voltage by a process called electromagnetic induction AC = alternating current Slide 57 If a magnet is moving out of the coil, or the other pole of the magnet is moving into it, there is a voltage induced in the opposite direction Slide 58 Slide 59 Vp / Vs = Np / Ns Voltage across primary coil Voltage across secondary coil Number of turns primary coil Number of turns secondary coil = 8 turns4 turns Transformer Slide 60 Rate/speed of rotation Strength of magnet/ magnetic field Number of turns/coils of wire Slide 61 a.c / alternating current Slide 62 Energy = power x time Power = energy / time Slide 63 0.78 2990 Slide 64 30 ohm Slide 65 Slide 66 P4 Explaining Motion P5 Electric Circuits P6 Radioactive materials Slide 67 Radioactive materials Slide 68 proton + neutron 0 electron - nucleus orbit / shell energy level An atom The nucleus is positively chargedso it attracts the negative electron Animation completed Slide 69 The Rutherford Scattering Experiment Alpha particles (positive charge) Thin gold foil Some particles passed through, some were deflected backwards How do scientists know about the structure of atoms? Particles passing through the foil indicated atoms have large amounts of space. The particles that were deflected back indicated the alpha particles had passed close to something positively charged within the atom (the nucleus) Slide 70 nucleus alpha radiation beta radiation gamma radiation When an unstable nucleus changes, what can happen ? Radioactive isotopes release radiation and the nucleus changes The behaviour of radioactive materials (radioactive decay) cannot be changed by chemical or physical processes Slide 71 Isotopes An isotope is an atom with a different number of neutrons: A radioisotope is simply an isotope that is radioactive e.g. carbon 14, which is used in carbon dating. 1) Alpha ( ) an atom decays into a new atom and emits an alpha particle (2 protons and 2 neutrons the nucleus of a helium atom) 2) Beta ( ) an atom decays into a new atom by changing a neutron into a proton and electron. The fast moving, high energy electron is called a beta particle. 3) Gamma after or decay surplus energy is sometimes emitted. This is called gamma radiation and has a very high frequency with short wavelength. The atom is not changed. Radioactive changes some nuclei that are unstable can become stable by emitting an alpha or beta particle Slide 72 Example Radium-226 undergoing alpha decay forms Radon-222, an alpha particle and releases energy. Example Polonium-218 undergoing beta decay forms Astatine-218, an electron and releases energy. Alpha decay Beta decay Slide 73 Radioactivity If a substance is capable of ALWAYS emitting radiation under any conditions we say it is radioactive. There are three types of radiation: ALPHA, BETA and GAMMA. Sheet of paper Few mm of aluminium Few cm of lead Slide 74 Background radiation Sources of background radiation Radiation dose measures the possible harm the radiation could do to the body. It is measures in millisieverts (mSv). The potential harm done depends on the amount of radiation the type of radiation Slide 75 Exposure to a radiation source outside your body is called irradiation If a radiation source enters your body, or gets on skin or clothes, it is called contamination Alpha particles are the most ionising so they are the most dangerous inside your body Employers must ensure that radiation workers receive a Radiation dose as low as reasonably achievable. Precautions taken are use protective clothing and screens.wear gloves and aprons wear special devices to monitor their dose Slide 76 treating cancersterilising equipment sterilising food Uses of gamma radiation it can kill cancer cells it can penetrate the outer casing and kill microbes it can kill microbes without harming the food Slide 77 Radon gas is harmful because it is radioactive. It produces ionising radiation that can damage cells. Medical imaging and treatment Radioactive materials cane be used to diagnose and cure many health problems. Radiotherapy is used to kill cancer cells Slide 78 Half life The HALF-LIFE of an atom is the time taken for HALF of the radioisotopes in a sample to decay At start there are 16 radioisotopes After 1 half life half have decayed (thats 8) After 3 half lives another 2 have decayed (14 altogether) After 2 half lives another half have decayed (12 altogether) = radioisotope= new atom formed Slide 79 A radioactive decay graph Time Count 1 half life A substance is considered safe once its activity drops to the same level as background radiation. Slide 80 Nuclear fission neutron U-235 nucleus ENERGY Smaller nucleus neutrons The energy released can be calculated from Einsteins equation : E = mc The fission of one atom can set off several more causing a chain reaction Slide 81 Nuclear reactor Nuclear waste High level waste this is spent fuel rods Intermediate level waste HLW decays to become ILW Low level waste protective clothing and medical equipment Slide 82 Nuclear fusion the nuclei of two hydrogen atoms join together and energy is released. Protons and neutrons in a nucleus are held together by a strong nuclear force, which acts against the electrical repulsive force between protons