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Year 1 1 AQA GCSE Physics Revision Booklet
Paper 1
Particle model of matter
Density of materials - know the density of a material is defined by the equation: density = mass/volume - ρ = m/V density, ρ, is measured in kilograms per metre cubed, kg/m^3 mass, m, is measured in kilograms, kg volume, V, is measured in metres cubed, m^3 How to explain the differences in density between the different states of matter in terms of the arrangement of atoms or molecules. How to explain differences in density between the different states How to describe practical methods to measure the density of regular and irregular sol- ids and a liquid.
The three states of matter – know The states of matter are solid, liquid and gas and how to recognise and draw simple dia- grams to model the difference in arrangement of particles between solids, liquids and gases. The names of the changes of state (Melting, freezing, boiling, evaporating, condensing, sublimation) How to use melting and boiling point data to decide the state of a substance
Changes of state Students should be able to describe how and that when substances change state (melt, freeze, boil, evaporate, condense or sublimate) and that mass is conserved. Changes of state are physical changes which differ from chemical changes
Internal Energy Internal energy is stored inside a system by the particles that make up the system. It is the total kinetic energy and potential energy of all the particles Heating changes the energy stored within the system by increasing the energy of the particles that make up the system. This either raises the temperature of the system or produces a change of state.
Temperature changes in a system and specific heat capacity If the temperature of the system increases, the increase in temperature depends on the mass of the substance heated, the type of material and the energy input to the system. The specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius. The following equation applies change in thermal energy = mass× specific heat capacity x temp change. change in thermal energy is measure in joules, J, mass, m, in kilograms, kg specific heat capacity, c, is measured in joules per kilogram per degree Celsius, J/kg °C temperature change, Δθ, is measured in degrees Celsius, °C.
Particle model of matter continued
Changes of heat and specific latent heat Latent heat is the energy needed for a substance to change state. When a change of state occurs, the energy supplied changes the energy stored (internal energy) but not the temperature. The specific latent heat of a substance is the amount of energy required to change the state of one kilogram of the substance with no change in temperature. energy for a change of state = mass × specific heat capacity x latent heat energy, E, is measured in joules, J; mass, m is measured in kilograms, kg specific latent heat, L, is measured in joules per kilogram, J/kg Specific latent heat of fusion is the change of state from solid to liquid Specific latent heat of vaporisation is the change of state from liquid to vapour Be able to interpret heating and cooling graphs that include changes of state. Be able to distinguish between specific heat capacity (a change in temperature is in- volved) and specific latent heat (a change of state is involved at constant temperature).
Particle motion in gases The molecules of a gas are in constant random motion. The temperature of the gas is related to the average kinetic energy of the molecules. Changing the temperature of a gas, held at constant volume, changes the pressure ex- erted by the gas. Be able to explain how the motion of the molecules in a gas is related to both its tem- perature and its pressure Be able to explain qualitatively the relation between the temperature of a gas and its pressure at constant volume.
Pressure in gases A gas can be compressed or expanded by pressure changes. The pressure produces a net force at right angles to the wall of the gas container Be able to use the particle model to explain how increasing the volume in which a gas is contained, at constant temperature, can lead to a decrease in pressure. For a fixed mass of gas held at a constant temperature: pressure × volume = constant pV=constant (p 1 V 1 = p 2 V 2 ) pressure, p, is measured in pascals, Pa; volume, V, is measured in metres cubed, m^3 Be able to calculate the change in the pressure of a gas or the volume of a gas (a fixed mass held at constant temperature) when either the pressure or volume is changed.
Increasing the pressure of a gas Work is the transfer of energy by a force. Doing work on a gas increases the internal energy of the gas and can cause an increase in the temperature of the gas. Be able to explain how, in a given situation e.g. a bicycle pump, doing work on an en- closed gas leads to an increase in the temperature of the gas.
Atomic Structure and Radioactivity continued
Radioactive Decay – know: That Radioactive decay is random and that the half-life of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve, or the time it takes for the count rate to fall to half its initial level. How to determine the half-life of a radioactive isotope from given information. How to calculate the net decline, expressed as a ratio, in a radioactive emission after a given number of half-lives. That radioactive isotopes have a very wide range of half-life values. The hazards associated with a radioactive material depends on the half-life.
Radioactive Contamination - know That radioactive contamination is the unwanted presence of radioactive atoms with the hazard being the due to the decay of the contaminating atoms. The type of radiation emitted affects the level of hazard. Irradiation is when an object is exposed to radiation, but does not become radioactive. How to compare the hazards associated with contamination and irradiation. The precautions to protect against hazards from radioactive sources. Recognise the importance for the findings of studies into the effects of radiation on humans to be published and shared so that the findings can be checked by peer review.
Background radiation - know Background radiation is around us all of the time. It comes from natural sources such as rocks and cosmic rays from space, man-made sources such as the fallout from nuclear weapons testing and nuclear accidents. The level of background radiation and radiation dose may be affected by occupation and/or location. Radiation dose is measured in sieverts (Sv) - 1000 millisieverts (mSv) = 1 sievert (Sv)
Uses of radiation Know that nuclear radiations are used in medicine for the exploration of internal organs and control or destruction of unwanted tissue. Be able to describe and evaluate the uses of nuclear radiations for exploration of inter- nal organs, and for control or destruction of unwanted tissue Be able to evaluate the perceived risks of using nuclear radiations when given data and consequences
Nuclear Fission – know that: Nuclear fission is the splitting of a large unstable nucleus (e.g. uranium or plutonium). Spontaneous fission is rare, for it to occur the unstable nucleus a neutron is absorbed. The nucleus undergoing fission splits into two smaller nuclei, roughly equal in size, and emits two or three neutrons plus gamma rays. Energy is released by the fission reaction. All of the fission products have kinetic energy and the neutrons may go on to start a chain reaction where the reaction is controlled in a reactor with controlled energy re- lease. The explosion of a nuclear weapon is caused by an uncontrolled chain reaction. How to draw/interpret diagrams representing nuclear fission/ chain reaction.
Nuclear Fusion – know that: Nuclear fusion is the joining of two light nuclei to form a heavier nucleus. In this process some of the mass may be converted into the energy of radiation.
Electricity
Circuit Symbols - You should know the circuit symbols below:
Electrical charge and current For electrical charge to flow through a closed circuit the circuit must include a source of potential difference. Electric current is a flow of electrical charge. The size of the electric current is the rate of flow of electrical charge. Charge flow, current and time are linked by the equation: Charge flow = current x time Q = It Charge flow Q, in coulombs, C, current I, in amperes, A (Amps is ok), time, t in seconds s. A current has the same value at any point in a single closed loop.
Current, Resistance and Potential Difference The current (I) through a component depends on both the resistance (R) of the compo- nent and the potential difference (V) across the component. The greater the resistance of the component the smaller the current for a given poten- tial difference (p.d.) across the component. Current, potential difference or resistance can be calculated using the equation: Potential difference = current x resistance V = I R Potential difference (V) in volts V, current (I) in Amps A and resistance (R) in ohms Ω. Be able to draw a suitable circuit diagram and explain how to complete a practical to investigate the factors affecting the resistance of an electrical circuit. Including the ef- fect of the length of wire at constant temperature and combinations of resistors in se- ries and parallel.
Resistors be able to explain that, for some resistors, the value of R remains constant but that in others it can change as the current changes. The current through an ohmic conductor (at a constant temperature) is directly propor- tional to the potential difference across the resistor. This means that the resistance re- mains constant as the current changes.
The resistance of components such as lamps, diodes, thermistors and LDRs is not con- stant; it changes with the current through the component.
Electricity - continued
Series and parallel circuits - continued How to explain the design and use of dc series circuits for measurement and testing purposes How to calculate the currents, potential differences and resistances in dc series circuits How to solve problems for circuits which include resistors in series using the concept of equivalent resistance.
Domestic uses and safety Direct and alternating potential difference – know Mains electricity is an ac supply In the UK the supply has a frequency of 50Hz and is about 230V Explain the difference between a direct (one direction only) and alternating (constantly changing direction) potential difference. Mains electricity – know Most electrical appliances are connected to the mains using three-core cable The insulation covering each wire is colour coded for easy identification. (live wire – brown, neutral wire – blue, earth wire – green and yellow stripes) The live wire carries the alternating p.d. from the supply so can be dangerous even when a switch in the mains circuit is open. The neutral wire completes the circuit. The earth wire is a safety wire to stop the appliance becoming live To explain the dangers of providing any connection between the live and earth. The p.d. between the live wire and earth is about 230V. The neutral wire is at, or close to, earth potential (0V). The earth wire is at 0V and only carries a current if there is a fault. Energy Transfers, Power – know Explain how the power transfer in any circuit device is related to the potential differ- ence across it and the current through it, and to the energy changes over time: Power = potential difference x current P = IV Power = (current)^2 x Resistance P = I^2 R Power P in Watts, W p.d. V in volts, V Current I, in amps, A Resistance R, in ohms Ω Energy transfers in everyday appliances Everyday electrical appliances are designed to bring about energy transfers. The amount of energy an appliance transfers depends on how long the appliance is switched on for and the power of the appliance. Describe how different domestic appliances transfer energy from batteries or ac mains to the kinetic energy of electric motors or the energy of heating devices. Work is done when charge flows in a circuit. The amount of energy transferred by electrical work can be calculated using the equa- tion: Energy transferred = power x time E = Pt Energy transferred = charge flow x potential difference E = QV
Electricity - continued
Energy transfers in everyday appliances Energy transferred = current x p.d. x time E = VIt Energy transferred E in joules J Power P in watts W Time t, in seconds, s Charge flow Q in coulombs Potential difference V in volts V Current I in amps A Explain how the power of a circuit device is related to the p.d across it and the current through it Explain how the power of a circuit device is related to the energy transferred over a giv- en time. Describe, with examples, the relationship between the power ratings for domestic electrical appliances and the changes in stored energy when they are in use. The National Grid The National grid is a system of cables and transformers linking power stations to con- sumers. Electrical power is transferred from power stations to consumers using the National grid. Step up transformers are used to increase the potential difference from the power sta- tion to the transmission cables then step-down transformers are used to decrease, to a much lower value, the potential difference for domestic use. Explain why the National Grid system is an efficient way to transfer energy. Static Electricity – know That when certain insulating materials are rubbed against each other they become elec- trically charged. Know how this happens in relation to the movement of negatively charged electrons and be able to describe the production of static electricity and spark- ing. What happens when electrically charged objects are brought close together and that this depends on their charge That attraction and repulsion between two charged objects are examples of a non- contact force and describe evidence (examples) of this.
Electric Fields – know that A charged object creates an electric field around itself. The electric field is strongest close to the charged object and diminishes with distance from the charged object. A second charged object placed in the field experiences a force. The force gets stronger as the distance between the objects decreases. How to draw the electric field pattern for an isolated charged sphere, explain the con- cept of an electric field, explain how the concept of an electric field helps to explain the noncontact force between charged objects as well as other electrostatic phenomena such as sparking.
Energy - continued
Energy changes in systems - continued Be able to explain the required practical to determine the specific heat capacity of one (or more) materials by linking the decrease of one energy store (or work done) to the increase in temperature and subsequent increase in thermal energy stored. For exam- ple the gain in thermal energy by a known mass of water will equal the loss in thermal energy of a known mass of metal, this can be used to determine the specific heat capac- ity of the metal. Power Power is defined as the rate at which energy is transferred or the rate at which work is done. Power = energy transferred/time (this equation must be recalled) P = E/t Power = work done / time (this equation must be recalled) P = W/t Power, P, in watts, W Energy transferred, E, in joules, J Time, t, in seconds, s Work done, W, in joules, J An energy transfer of 1 joule per second is equal to a power of 1 watt. Be able to give examples that illustrate the definition of power e.g. comparing two elec- tric motors that both lift the same weight through the same height but one does it fast- er than the other. Conservation and dissipation of energy – Energy transfers in a system Energy can be transferred usefully, stored or dissipated, but cannot be created or de- stroyed. Be able to describe with examples where there are energy transfers in a closed system, that there is no net change to the total energy. Be able to describe, with examples, how in all system changes energy is dissipated, so that it is stored in less useful ways. This energy is often described as being ‘wasted’. Explain ways of reducing unwanted energy transfers, for example through lubrication and the use of thermal insulation. The higher the thermal conductivity of a material the higher the rate of energy transfer by conduction across the material. The different thermal conductivity of metals can be shown by sticking drawing pins onto a strip of metal using wax, heating one end of the strip and monitoring the time for pins to drop (when heating several different metals at once) Be able to describe how the rate of cooling of a building is affected by the thickness and thermal conductivity of its walls. Required practical to investigate the effectiveness of different materials as thermal in- sulators and the factors that may affect the thermal insulation properties of a material. Efficiency The energy efficiency for any energy transfer can be calculated using the equation: Efficiency = useful output energy transfer / total input energy transfer (learn this) Efficiency may also be calculated using the equation: Efficiency = useful power output/total power input Be able to use efficiency values as either a percentage or a decimal Describe ways to increase the efficiency of an intended energy transfer.
Energy - continued
National and Global Energy Resources The main energy resources available for use on Earth include: Fossil fuels (coal, oil and gas), nuclear fuel, bio-fuel, wind, hydro-electricity, geothermal, the tides, the Sun and water waves. A renewable energy resources is one that is being (or can be) replenished as it is used. The uses of energy resources include transport, electricity generation and heating. Be able to describe the main energy sources available Distinguish between energy resources that are renewable and energy resources that are non-renewable Compare ways that different energy resources are used, the uses to include transport, electricity generation and heating To understand why some energy resources are more reliable than others. Describe the environmental impact arising from the use of different energy resources Explain patterns and trends in the use of energy resources. Be able to consider environmental issues that may arise from the use of different ener- gy resources. Show that science has the ability to identify environmental issues arising from the use of energy resources but not always the power to deal with the issues because of politi- cal, social, ethical or economic considerations.
Space Physics - continued
Red-shift – continued Since 1998 onwards, observations of supernovae suggest that distant galaxies are re- ceding ever faster. Explain qualitatively the red shift of light from galaxies that are receding Explain the change of each galaxy’s speed with distance is evidence of an expanding universe Explain how red-shift provides evidence for the Big Bang model Explain how scientists are able to use observations to arrive at theories such as the Big Bang Theory. Explain that there is still much about the universe that is not understood for example dark mass and dark energy.
Waves
Transverse and longitudinal waves Be able to describe the difference between longitudinal and transverse waves including examples of each (e.g. ripples / light for transverse & sound (compression waves) for longitudinal. Describe evidence that, for both ripples on a water surface and sound waves in air, it is not the wave and not the water or air itself that travels. Properties of waves Be able to describe wave motion in terms of their amplitude, wavelength, frequency and period. Amplitude – maximum displacement of a point on a wave away from its undisturbed position. Wavelength – distance from a point on one wave to the equivalent point on the adja- cent wave. Frequency – number of waves passing a point each second. Period – 1/frequency [T= 1/f](equation on the physics equation sheet) Period, T, in seconds, s Frequency, f, in hertz, Hz The wave speed is the speed at which the energy is transferred (or the wave moves) through the medium. All waves obey the wave equation: Wave speed – frequency x wavelength [v=f λ] (learn this equation) Wave speed, v, in metres per second, m/s Frequency f, in hertz, Hz, Wavelength, λ, in metres, m Be able to identify amplitude and wavelength from given diagrams Describe a method to measure the speed of sound waves in air and describe a method to measure the speed of ripples on a water surface. Be able to show how changes in velocity, frequency and wavelength, in transmission of sound waves from one medium to another are inter-related. Required practical – be able to identify the suitability of apparatus to measure the fre- quency, wavelength and speed of waves in a ripple tank and waves in a solid and take appropriate measurements. Reflection of waves Be able to construct ray diagrams to illustrate the reflection of a wave at a surface Be able to describe the effects of reflection, transmission and absorption of waves at material interfaces Required practical – investigate the reflection of light by different types of surfaces and the refraction of light by different substances.
Waves continued
Sound waves Sound waves can travel through solids causing vibrations in the solid. Within the ear, sound waves cause the ear drum and other parts to vibrate which caus- es the sensation of sound. The conversion of sound waves to vibrations of solids works over a limited frequency range. This restricts the limits of human hearing. Explain why the conversion of sound waves to vibrations only works over a limited fre- quency range Know the range of normal human hearing is from 20Hz to 20kHz Waves for detection and exploration Be able to explain in qualitative terms, how the differences in velocity, absorption and reflection between different types of wave in solids and liquids can be used both for de- tection and exploration of structures which are hidden from direct observation. Ultrasound – frequency higher than upper limit of human hearing. Ultrasound is par- tially reflected when it meets a boundary between two different media. The time taken for reflections to reach a detector can be used to determine how far away such a boundary is. Ultrasound can therefore be used for both medical and industrial imaging. Seismic waves are produced by earthquakes. P-waves are longitudinal, seismic waves. P- waves travel at different speeds in solids and liquids. S-waves are transverse, s- waves cannot travel through a liquid. P-waves and S-waves provide evidence for the structure and size of the Earth’s core. The study of seismic waves produced new evi- dence leading to discoveries about parts of the earth which are not directly observable. Echo sounding, using high frequency sound waves is used to detect objects in deep wa- ter and measure depth Electromagnetic waves – Types EM waves are transverse waves that transfer energy from the source of the waves to an absorber. EM waves form a continuous spectrum and all travel at the same velocity through a vacuum or air. Waves are grouped in terms of wavelength and frequency. From long to short wave- length (low to high frequency) the groups are: Radiowaves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays. Our eyes detect only visible light Be able to give examples that illustrate the transfer of energy by electromagnetic waves. E.g. heating effect of sunlight – IR radiation Properties of electromagnetic waves Different substances may absorb, transmit, refract or reflect EM waves in ways that vary with wavelength. Some effects e.g. refraction, are due to the difference in velocity of the waves in differ- ent substances. Be able to construct ray diagrams to illustrate the refraction of a wave at the boundary between two media. Be able to use wave front diagrams to explain refraction in terms of the change of speed that happens when a wave travels from one medium to a different medium. Required practical – investigate how the amount of IR radiation absorbed or radiated by a surface depends on the nature of that surface Radio waves can be produced by oscillations in electrical circuits. When radio waves are absorbed they may create an alternating current with the same frequency as the radio wave itself, so radio waves can themselves induce oscillations in an electrical circuit. Changes in atoms and the nuclei of atoms can result in electromagnetic waves being
Black body radiation – emission and absorption of IR radiation All bodies (objects), no matter what temperature, emit and absorb infrared radiation. The hotter the body, the more infrared radiation it radiates in a given time. A perfect black body is an object that absorbs all of the radiation incident on it. A black body does not reflect or transmit any radiation. Since a good absorber is also a good emitter, a perfect black body would be the best possible emitter. Perfect black bodies and radiation Be able to explain that all bodies emit radiation That the intensity and distribution of any emission depends on the temperature of the body. Be able to explain how the temperature is related to the balance between incoming ra- diation absorbed and radiation emitted, using everyday examples which illustrate this balance and the example of the factors which determine the temperature of the Earth. Use information or draw/interpret diagrams to show how radiation affects the temper- ature of the Earth’s surface and atmosphere.
Forces and their interactions (^)
Scalar and vector quantities: Scalar quantities have magnitude only. Vector quantities have magnitude and associated direction. A vector may be represented by an arrow. The length of the arrow represents the magnitude and the direction of the arrow the direction of the vector quantity. Contact and non-contact forces A force is a push or pull that acts on an object due to the interaction with another ob- ject. All forces between objects are either: Contact forces (physically touching eg friction, air resistance, tension and normal con- tact force) Non-contact forces (physically separated eg gravitational, electrostatic and magnetic forces) Forces are vector quantities Make sure you can describe the interaction between pairs of objects which produce a force on each object, the forces to be represented as vectors. Gravity Weight is the force acting on an object due to gravity. The force of gravity close to the earth is due to the gravitational field around the Earth. The weight of an object depends on the gravitational field strength at the point where the object is. Weight = mass x gravitational field strength (Learn and recall this equation) W=mg (g=9.8N/kg – this will be given to you) The weight of an object may be considered to act at a single point referred to as the ob- ject’s ‘centre of mass’. Weight and mass are directly proportional. W m (the symbol means ‘proportional to’ here) Weight is measured using a calibrated spring-balance (newton meter) Resultant Forces A number of forces acting on a point can be replaced with a single force that has the same effect as all the original forces acting together. This single force is called the re- sultant force. You need to be able to calculate the resultant of two forces acting in a straight line. You need to be able to resolve a single force into two components acting at right angles
to each other by scale diagram (you can use trigonometry and Pythagoras but be careful to read the question carefully they may want to see a scale diagram) Draw free body diagrams and use them to describe examples where several forces lead to a resultant force on an object including balanced forces where the resultant force is zero. Use vector diagrams to illustrate resolution of forces, equilibrium situationa sn deter- mine the resultant of two forces at right angles including both magnitude and direction (Scale drawings only) Work done and Energy transfer. Work is done when a force acts on an object causing it to more through a distance. Work = force x distance (learn and recall this equation). W = F s 1Joule of work is done when a force of one newton causes a displacement of 1 metre. Make sure you can describe the energy transfer involved when work is done. Convert between newton-metres Nm and Joules (1Nm = 1J) Work done against frictional forces acting on an object causes a rise in the temperature of the object. Forces and Elasticity Give examples of the forces involved in stretching, bending or compressing an object. Explain why, to change the shape of an object more than one force has to be applied (limited to stationary objects only) Describe the difference between elastic deformation and inelastic deformation caused by stretching forces. The extension of an elastic object, such as a spring, is directly proportional to the force applied, provided that the limit of proportionality is not exceeded. Force = spring constant x extension F = ke (learn and recall this equation) Make sure you can describe the difference between linear and non-linear relationship between force and extension and use the linear case to calculate a spring constant The equation is valid for compression of an elastic object where e is the compression in this case rather than extension. A force stretching a spring does work and this elastic potential energy is stored in the spring. Provided the spring is not elastically deformed, the work done on the spring and the elastic potential energy stored are equal. Be able to interpret data from an investigation of the relationship between force and extension. Calculate work done in stretching (or compressing) a spring (up to the limit of propor- tionality) using the equation: Ee = ½ ke Elastic potential energy = ½ x spring constant x (extension)2 (You will be given this equation) Required Practical 6 – investigating the relationship between force and extension for a spring Moments, levers and gears Moment of a force = force x perpendicular distance between force and pivot(learn and recall this equation) Moment measured in Nm For equilibrium the total clockwise moment equals the total anti-clockwise moment. A simple lever and a simple gear system can both be used to transmit the rotational ef- fects of forces. Make sure you can explain how levers and gears transmit the rotational effects of forc- es.
Acceleration Average acceleration = change in velocity / time taken a = (v-u)/t (learn and recall this equation acceleration is measured in m/s Be able to estimate the magnitude of everyday accelerations Acceleration can be calculated from the gradient of a velocity time graph. The displacement of an object is calculated from the area under a velocity-time graph. Make sure you can draw v-t graphs from measurements and interpret lines and slopes to determine acceleleration. Interpret enclosed areas in v-t graphs to determine distance (or displacement) trav- elled. Measure area under a v-t graph by counting the squares. For uniform acceleration (final velocity)2-(initial velocity)2 = 2 x acceleration x displacement v2 – u2 = 2as (be able to use this equation it will be given to you on the sheet) Near the earth’s surface any object falling freely under gravity has an acceleration of about 9.8m/s An object falling through a fluid initially accelerates due to the force of gravity. Eventu- ally the resultant force will be zero and the object will move at its terminal velocity. Make sure you can draw and interpret v-t graphs for objects that reach terminal veloci- ty including interpreting the changing motion in terms of the forces acting. Newton’s First Law If the resultant force on an object is zero and: The object is stationary it will remain stationary The object is moving the object will continue to move at the same speed and in the same direction i.e. with the same velocity. A vehicle travelling at constant speed has balanced forces (resistive and driving forces are equal but in opposite directions). If the velocity (speed and/or direction) is changing then an resultant force must be act- ing on the object. The tendency of objects to continue in their state of rest or of uniform motion is called inertia. Newton’s Second Law The acceleration of an object is proportional to the resultant force acting on the object and inversely proportional to the mass of the object. Resultant force = mass x acceleration F = ma Inertial mass is a measure of how difficult it is to change the velocity of an object Inertial mass is the ratio of force over acceleration F/a Be able to estimate the speed, accelerations and forces involved in large accelerations for everyday road transport. Recognise and use the symbol ~ for an approximate value or answer. Required practical activity 7 – investigate the effect of varying the force on the accelera- tion of an object of constant mass and the effect of varying the mass of an object on the acceleration produced by constant force. Newton’s Third Law Whenever two objects interact, the forces they exert on each other are equal and op- posite. Be able to apply this law to examples of equilibrium situations (e.g. a book on a shelf, a car on the road, a balloon propelled toy car (backward motion of air out of balloon pro- duces equal but opposite force on car propelling it forward) Stopping Distance:
Stopping distance = thinking distance + braking distance Thinking distance = distance travelled during the driver’s reaction time. Braking distance = distanced travelled while the brakes are applied until the car stops. For a given braking force, the greater the speed the greater the stopping distance. Estimate how the distance for a vehicle to make an emergency stop varies over a range of speeds typical for that vehicle. Interpret graphs relating speed to stopping distance for a range of vehicles. Reaction time: Reaction time varies between people. Typical values range from 0.2 – 0.9s Reaction time increased by: tiredness, drugs, alcohol and distractions. Explain methods to measure human reaction time and recall typical results. Interpret and evaluate measurements from simple methods to measure the different reaction times of students. Evaluate the effect of various factors on thinking distance based on data Factors affecting braking distance Adverse road and weather conditions, poor condition of the vehicle’s brakes or tyres. Make sure you can explain how these factors affect the distance required for road transport vehicles to come to rest in emergencies and the implications for safety. Estimate how the distance required for road vehicles to stop in an emergency varies over a range of typical speeds. In the brakes, work is done by the friction force between the brakes and the wheel to reduce the kinetic energy of the vehicle and the temperature of the brakes increases. The greater the speed of a vehicle, the greater the braking force needed to stop the ve- hicle in a certain distance. The greater the braking force the greater the deceleration of the vehicle. Large decel- erations may lead to brakes overheating and/or loss of control. Make sure you can explain these dangers Estimate the forces involved in the deceleration of road vehicles in typical situations on a public road. Momentum Momentum is a property of moving objects defined by the equation Momentum = mass x velocity (learn and recall this equation) p = mv momentum is measured in kg m/s Conservation of momentum In a closed system the total momentum before an event is equal to the total momen- tum after the event. Conservation of momentum Make sure you can describe and explain examples of momentum in an event such as a collision and complete calculations involving the collision of two objects for example. Recall an experiment using the air track and light gates to investigate momentum con- servation in collisions. Changes in momentum When a force acts on an object that is moving or able to move a change in momentum occurs. F = ma and a=(v-u)/t combine to give F=mΔv/Δt (you will be given this equation on the sheet) Where mΔv is the change in momentum i.e. force equals rate of change of momentum. Use the idea of rate of change of momentum to explain safety features such as: air bags, seat belts, gymnasium crash mats, cycle helmets and cushioned surfaces for play- grounds. Apply the equations relating force, mass, velocity and acceleration to explain how the
