Physics Key Points

A pluck tidy sum do genius of quaternary things to an object 1. Make it hurrying up accelerate. 2. Make it s wretched tear decelerate. 3. salmagundi its worry. 4. Change its shape. If something is doing one of these four things there must be net issue acting upon it. Newtons First Law Every physical structure continues in a state of rest or uniform proceeding unless(prenominal)(prenominal) acted upon by an external force. Something with step up net force acting on it go forth either stay still or guide at a constant speed in a straight line until you sacrifice a force to it. F = ma Newtons Second Law F is the force in Newtons, N. m is the vision in kilograms, kg. a is the acceleration in m/s2. This shows that if you keep the mass constant and figure of speech the applied force the acceleration ordain take over. Hookes Law, elastic and plastic de specifyor F = kx An elastic signifi put upt is one that leave alone re let go to its verit fit shape when the fo rce applied to it is taken absent. A plastic (or inelastic) strong is one that stays deformed after you drive home taken the force away. If you apply too big a force a material provide lose its elasticity. In solids If a force is applied everyplace a sm entirelyer surface argona you loaf a large pressure.Pressure rear be calculated utilise the following comparison Pressure = force/argona Force exit be in Newtons, N. Area will be in either m2 or cm2. If the bea is in m2 indeed the pressure will be heedful in Pascals or N/m2. If the bea is in cm2 thus the pressure will be in N/cm2. In lucids 1. Pressure increases with depth. 2. Pressure acts equ completely(a)y in whole modes. 3. Pressure is inherited by dint of liquids. Hydraulics All hydraulics systems execute be ingest the pressure is the alike(p) with knocked out(p) the system. A really good example of this is a machine brake system. You pack to know all about this for your exams.In acceleratores Althou gh gases argon compressible (squashy) they exert a pressure because of the gas darkseticles bouncing preserve carreled things. Boyles Law For a fixed mass of gas the pressure x the peck of the gas stays the comparable. In other words, as you glut a gas its pressure will go up and its volume will blend less. Important point The temperature and mass of gas must stay the same for this to be true We give the axe write this as Pressure x volume = constant or P1V1 = P2V2 Moments Moments make things turn or rotate. They ar ca utilize by forces unless are not forces themselves. analogous forces, arcseconds dupe a manner.We say they are either clockwise or anti-clockwise, to show which way they will make something turn. The bigger the force do the turning government issue the bigger the moment will be. The further the force is from the pivot the bigger the moment will be. The size of a moment can be calculated using Moment = Force x Distance Force is mensurable in Newtons, N . Distance is heedful in either m or cm. If the exceed is in m then the moment will be deliberate in Nm. If the master(prenominal)tain is in cm then the moment will be deliberate in Ncm. Distance As we all know, the distance between dickens points is how far apart they are.In science, we normally use metres as our social unit. We oft represent how the distance between two points converts using a distance time graph. accelerate cannonball on is how unwavering something is going. It is how quickly something covers a authoritative distance and can be campaigned out using the equation Speed = distance/time Acceleration This is how quickly something gets red-hot. So if you were running and get 1m/s faster every second you would have had an acceleration of 1 m per second per second. We normally write this 1 m/s2. We perish out by the equation Acceleration = remove in speed/time takenFrequency, castlength, amplitude and time period are utilize to describe turn overs. Waves can be transverse or longitudinal. Transverse waves the shakiness is at right angles to the wave motion, e. g. light, water waves and the electromagnetic spectrum waves. Longitudinal waves the vibe is parallel to the wave motion, e. g. perish and some universequake waves. Wave Speed (m/s) = Frequency (Hz) x wavelength (m) Reflection is the bouncing of waves off a surface. at that place are collar principles of reproach that you need to know. 1. The angle of incidence of all time equals the angle or reflection. 2.The distance from the object to mirror is the same as the distance from the mirror to the image. 3. The image is ever the same size as the object that is laterally inverted. Refraction is the bending of a wave when it goes from one substance into another. Refraction happens because the speed and wavelength of the wave changes as the wave goes into the other substance. The frequency of the wave stays the same. Total internal reflection happens when the angl e of incidence, of a wave going from a substance into air, is great than the critical angle. The wave bounces off the boundary, obeying the recovers of reflection.Dispersion of white light produces a spectrum. This is ca employ by refraction. climb down of different frequencies is refracted by different amounts. Red is refracted the to the lowest degree and violet the near. This causes white light to be split up into seperate colours. Diffraction is the airing out of a wave as it goes by dint of a gap, or around an object. The smaller the gap or the larger the wavelength the greater the diffraction. Diffraction is nearly in force(p) when the size of the gap is approximately the same as the wavelength of the wave. You will need to be able to draw diagrams showing how waves reflect, refract and diffract. proceed waves are cause by particles vibrating. The frequency of the vibration decides the pitch of the sound. The amplitude of the vibrations decides the tawdriness of the sound. Ultrasound waves are high frequency sound waves, which are beyond the human hearing range. Ultrasound is used for seeing babies in the womb, detection cracks in metal and cleaning instruments. Waves can be represented on an scope screen, which can be used to valuate the characteristics of the waves. You should be able to stripping the amplitude and time period of a wave from an oscilloscope screen.The electromagnetic spectrum is a serial publication of waves that all move at the same speed in a vacuum. They are all transverse. separately part of the spectrum has different uses and dangers. Each part of the spectrum has a different frequency and wavelength. da Gamma waves are at the high frequency end of the spectrum. Radio waves are at the low frequency end. You will need to know the uses and dangers of severally part of the spectrum. Different surfaces and materials absorb different frequencies of waves. White surfaces reflect close waves. Black surfaces absorb most waves. Information can be carried along copper cables as galvanising signals, or long optical fibres as electromagnetic wave pulses. optical fibres have advantages over copper cables. Optical fibres can carry to a greater extent information the signals can travel faster and lose less vim as they travel along the cable. at that place are two types of signals, analogue and digital. Analogue signals have a regular range of values. Digital signals have save two values, on (1) and off (0). Digital signals have advantages over analogue signals. Digital signals are easier to station as they are less affected by noise it is as well as possible to send more information, in a sealed time, as a digital signal than as an anologue signal.Types of pushing goose egg can not be created or destroyed it can only change from one form into another. at that place are galore(postnominal) types of dexterity including, sound alter light kinetic nuclear potential readiness energizing zippo is front end energy. Potential energy is investment companyd energy. There are three important forms of potential energy including gravitational, chemical and elastic. Sankey diagrams can be used to represent energy changes. The size of the arrows represents the amount of that type of energy. Energy is measured in Joules, J or kilojoules, kJ. Conduction Heat energy everlastingly moves from hotter objects to colder objects.Heat energy is conducted through solids by particles vibrating and passing on the movement to neighbouring particles. Metals are best at conducting awaken. As well as the vibrating particles, they move the heat up energy by free electrons moving between their atoms. The poorest directors are gases as their molecules are too far apart to affect each(prenominal) other much. Air is a very bad conductor. Most insulators train because of trapped air. Convection Convection is hot gases or liquids rising and cooler gases and liquids sinking to tack it. As substances heat up the density decreases, which is what makes them float.This movement of molecules is called a convection live. It can only happen in a gas or liquid where the molecules are free to move around. Radiation Radiated heat energy is unseeable radiation. All hot objects radiate heat. Black, dull surfaces are the best emitters of heat radiation. Lighter, shinier surfaces are poor radiators of heat. Radiated heat can overly be preoccupied by cooler objects. Black is the best absorber. Surfaces coloured silver or white will reflect the radiated heat. Ways to save energy in the home Reducing heat losses from a home path less damage to the environment and depress heating bills.Installing separation costs money. The payback time is how long it takes for the savings to cover the cost. Each strategy has to reduce conduction, convection, radiation or any combination of them. leafy vegetable strategies are double-glazing, loft insulation, tank lagging, lined curtains, cavi ty wall insulation, block up up disused fireplaces and putting foil exactlytocks radiators. Other preservation strategies hold using of low-energy light bulbs, turning down heating thermostats, sufficient draught excluders and switching off unattended appliances. Non-renewable fires and power postThe fogy fuels are oil, gas and coal. They are non-renewable, which means that they can not be replaced. They will reddentually run out. These fuels have more uses but the main ones are heating, transport and generating electrical energy. In power stations, the fuel is burnt and the heat turns water into steam. That steam pushes around a turbine that is connected to a beginning. The generator produces electricity. This mould is the same for all power stations. Nuclear power stations dont burn the fuel. Uranium fuel sustains heat that turns water into steam reasonable like in other power stations.Nuclear accidents are rare, but can be serious. The go off from the reactors can b e radioactive. It is easy to store it safely for now but it will stay radioactive for years. environmental impacts of burning fuels Carbon dioxide is the most common of several gases that contribute to the greenhouse effect. The result is global warming. This would result in the weather world more extreme and the ice caps releaseing raising the sea levels. Sulphur dioxide is the most common cause of panelling rain. It dissolves in rainwater to form an acid. The acid rain harms plants, animals and stone bailiwick.Alternative energy sources Most of the alternative energy sources are renewable. This means there is either an endless supply of them so that they will not run out, or they can be easily replaced. hydroelectric power is only possible where the geology is right, such as Scotland. Water runs fast down an incline and turns a turbine. Some developing countries get all their energy from HEP schemes on large dams. The large lake do behind the dam drastically alters the surrou ndings. Waves and tides have a lot of energy. Few schemes endure because of technological problems and environmental objections.Solar power converts the suns energy into electricity using solar panels. These panels are expensive to make. Wind farms are groups of wind turbines that generate electricity from wind. Some commonwealth dont like wind farms because they spoil the gaze or make a noise. Geothermal energy uses the natural heat in volcanic rock to generate electricity. Gas called methane is produced when matter rots. This gas can be used to generate heat to produce electricity. enthusiastic combat is not a way to avoid pollution but it does preserve fossil fuels as well as avoid rubbish having to be put in landfill sites.Crops can be grown to be burnt in a power station. Another version of this is to process the crops into alcohol and use it instead of petrol in cars. Work is do whenever a force acts over a distance, e. g. a car ride produces a forward force to move the car a certain distance. Energy is measured in Joules, J. The work done or energy transferred can be calculated using Work done or energy = force x distance When working out the work done the force must be in the same direction as the movement. If more than one force is acting in that direction then the resultant force must be used.Kinetic energy is the amount of movement energy an object has. Kinetic energy can be calculated using Kinetic energy = ? x mass x velocity2 Gravitational potential energy is the extra amount of stored energy an object has because it is higher up. GPE can be calculated using Change in gravitational potential energy = mass x staidness x change in height This is the same thing as GPE = weight x height Power is the rate at which work is done, or in other words, the amount of energy transferred per second. Power is measured in Watts, W or J/s. Power can be calculated usingPower = energy transferred / time taken Or Power = work done / time taken Energy is a g reat deal lost to the surroundings as heat energy. This is wasted energy as it cannot be easily used again. Efficiency tells us how much energy is wasted when an energy transfer has happened. The more efficient something is the less energy that is wasted. Efficiency can be calculated using Power out/power in*100 =efficiency in % Energy out/energy in*100=efficiency in % Static electrical energy Static Charge Static charge is a charge that cant move. There are two kinds optimistic (+) and negative (-).All atoms contain positive particles (protons) and negative particles (electrons) but because they contain the same physical body of protons and electrons they have no overall charge. Static electricity is caused by an atom having too many or too few electrons (e-). A Van de Graff Generator is a machine that generates huge amounts of static charge, by rubbing electrons off a roller and depositing them on the metal dome. Induction and Earthing The basic rule you need to know is that lik e charges repel and opposite charges attract. Induction This is the effect caused when a charged object causes electrons in another object to move.This causes the neutral object to become attracted to the charged object. Earthing If enough charge builds up on an insulator, the charge can leap the gap, causing a spark. This can be prevented by discharging the object, gradually. This is called earthing. Useful Static Static electricity is used in many useful machines like photocopiers and smoke stacks (to exact pollution from the smoke). Nasty Static If clouds get charged up enough, you get lightning, the biggest spark of all. Static can also be dangerous when refuelling aircraft. The fuel rubs against the side of the hose and lots of charge builds up.If the plane isnt earthed, the spark can blow the plane up. Basic Circuits up-to-the-minute, electromotive force and Resistances Current This is a measure of the flow of electrons around a turn (measured in Amperes or Amps). Volt age This is a measure of how much energy the electrons are carrying around the tour of duty (measured in Volts). Resistance This is a measure of how hard it is for the purple to travel through a part of the lick (measured in Ohms). Direction trouble Current flows from the positive (+ve) terminal of the battery to the negative (-ve). This is called conventional on-line(prenominal) flow.The problem is, electrons are negatively charged, so they want to get away from the -ve and go to the +ve. So if electrons are going left to right, you say that the sure is going right to left. Circuits An ammeter inevitably to measure the flow of charge, so it is in series. This means that all the charge has to flow through it and can be counted. It also means that an ammeter needs to have a very low resistance. A voltmeter measures voltage across a component, which you may have perceive as potential difference. This means it is in parallel and it also needs a high resistance (otherwise all the current would flow through the meter instead f the component). Series Circuits Current in series same all the way round (all the current has to flow through everything). Voltage in series voltages across each component lead up to the numerate voltage supplied by the battery, as they have to character the voltage between them (A) = (B) + (C) in the diagram. Higher resistances will need more of the voltage. Final point resistors in series To work out the total resistance of two resistors, just add them together. This is because the current has to go through both of them. Parallel Circuits Voltage in parallel all voltages the same.Current in parallel the current is shared out between the processes, but recombines near the battery. In the diagram (A) = (B) + (C) = (D). How much current each branch gets depends on the individual resistors bigger resistance = lower current. Resistance in parallel you dont normally have to work out numbers, but the rule of thumb is that the total resistance of two resistors in parallel is less than the lowest individual resistor. Circuit Symbols Cells and Batteries strictly speaking one cell represents 1. 5V, but of you write the voltage above it (e. g. 6V), most people will at a lower placestand the cell has 6 volts. Power Supplies come in all shapes and sizes just label them as you want. Switches several types, Ive shown the main two that you will come across Lamps/Bulbs either symbol could be used it doesnt matter. Resistors a few types Fixed, Variable (you can change the resistance), Thermistor (as it gets hotter, its resistance decreases) and Light Dependent Resistor or LDR (the more light that shines on it, the lower its resistance gets). Diode A diode is like an electrical valve, it only lets current flow one way.If it is connected with the arrow pointing to the negative terminal, current can easily flow, if it is the other way round, it will block the current. A LED or Light Emitting Diode is just the same turf out it gives off light Ohmmeter is connected directly to a resistor, of any kind, to find its resistance (no other circuit is used with it) Check in your course to see if there are anymore you need to know drive in Your Formulae Ohms Law The equity actually says that the resistance of a metal conductor is the same whatever the current unless its getting hotter.However most people think of these equations when the law gets mentioned V=IR and so on, Voltage (V) in Volts, Current (I) in Amps and Resistance (R) in Ohms. Charge (Q) in Coulombs, cartridge clip (t) in seconds and Power (P) in Watts. Always remember to show all your working out, including writing the formula properly (not just the triangle ) and hold offing your units (e. g. check for mV or kW instead of V or W) Prefixes These are little letters added to units to make them a different size, but always use the base unit if unsure.Base units are given in the twingeics, the ones to watch for are time (seconds) and mass (kilograms not grams). Prefixes Name comfort Example M Mega x 1,000,000 1MW = 1,000,000W k kilo x 1,000 1kg = 1,000g c centi ? 100 1cm = 0. 01m m milli ? 1,000 1ms = 0. 001s Mains Supply (AC and DC)We use two main sorts of electrical supplies, DC and AC. DC This is Direct Current. The current flows in one direction only and has a consistent value. Provided by batteries or DC adaptors/transformers that stack into the mains supply. AC This is Alternating Current. The current flows first one way then the other at a frequency of 50Hz. AC is what comes out of the mains sockets, unremarkably at around 240V. The Ring Main This is the name given to the circuit in your home. You only need to know that it is a parallel circuit and that the lighting circuit is separate from the circuit for sockets.The National Grid This is the circuit that carries electricity all around the country, from the power stations to homes and businesses. Producing the Power Energy is produced by burning f uel which turns water to steam, this drives a turbine, which make electricity via a generator. This electricity is a very high voltage and is passed over the National grid to a step down station then passed straight to your home. Why the High Voltage? High voltage is used over the National grid, to keep current low. This stops energy being wasted. Energy and the Cost Kilowatt-hours (kWh)The kilowatt-hour is the common unit used by energy companies to measure electricity. This is a unit of energy not power or time. It is the amount of energy if a 1kW appliance was left on for 1 hour. The Cost 1kWh of electrical energy costs around 6p, though it may change depending on your supplier. So multiplying the number of Kilowatt-hours you use by the unit cost (approx 6p), give you the total cost of the electricity you use. Safety A common question is to give you a picture of domestic joy and get you to identify the hazards, such as the person sticking their fingers in the toaster. Things to look for are . bad wiring, 2. water near appliances, 3. too many double plugs/adaptors, 4. Frayed wires. Just use your common sense and you should get some easy marks Wiring a Plug unitary big problem used to be wiring plugs. By law now, all new appliances are fitted with one already, which helps, but you do need to know whats going on inside there Fuses Fuses help cheer the circuit against faults. The key thing is to get the wire just thick enough to carry the current you want, but thin enough to melt if there is a current surge. Fuse Ratings Common sizes are 3, 5 and 13Amp fuses, but there are many others.Always choose one slightly higher than the current rating of the appliance, so that it doesnt blow under normal conditions. Circuit Breakers Fuses are not always effective at protecting you, so circuit breakers are also used. They automatically compare the current entering and leaving the circuit and even if there is the tiniest difference they trip off. Earth The Earth (yes, I do mean our planet) is very good at soaking up loose charge. The earth in your house is probably connected to the plumbing (goes to ground) or a large metal spike in the ground somewhere. Double breakupIf something is completely cased in an insulator, like plastic, it is said to be double insulated, and does not need earthing. You cant get a shock from the case Atoms are made up of protons electrons Neutrons. Protons and neutrons are in the meat and the electrons orbit the nucleus. Protons have a positive charge, electrons have a negative charge and neutrons have no charge. The shape of the atom was discovered using the alpha-scattering audition. This showed the original plum-pudding beat to be wrong Atomic notation is used to describe atoms. The top number is the mass or nucleon number.It tells us how many protons and neutrons there are in the nucleus. The bottom number is the proton or atomic number, which tells us how many protons are in the nucleus. During reactions the total number of protons and neutrons must stay the same. Isotopes of an ingredient have the same number of protons but a different number of neutrons in the nucleus. It is this different number of neutrons that makes some isotopes unstable and radioactive. These isotopes are called radioisotopes. ionization is where an electron is removed from a neutral atom, leaving the atom with a positive charge.Radiation causes ionisation. This can be used to detect radiation, as the amount of ionisation can be measured with a Geiger-Muller tube. ionisation can damage or kill living cells, this can cause cancer to develop. Alpha particles, beta particles and gamma waves are the three main types of radiation emitted during radioactive decay. All three types of radiation are emitted from the nucleus of the atom. When radiation is emitted the unstable atom loses energy to become more stable. If alpha or beta particles are emitted, new elements are formed because of the change in the number of pro tons in the nucleus.Alpha, beta and gamma radiation all behave slightly differently due to the way they are made up. Alpha ionises the most over a small distance but is not very penetrating. Gamma is the most penetrating but ionises less over the same distance. Decay equations can be used to work out what new daughter element will be produced when radioactive decay takes place. Safety precautions must be taken when handling radioactive substances. These include, using long handled tongs, pointing sources away from people, wearing lead lined clothing, not inhaling or eating sources.The half(prenominal)-life of a substance is the time it takes for half of the original parent atoms to decay. It is also the time it takes for the count rate of a substance to fall to half the original value. Radiation is used in medicine to cure cancer, in industry to detect the thickness of materials and in dating. Background radiation is radiation that is produced around us all of the time. Sources inc lude certain rocks, cosmic radiation, radon gas in the air, nuclear waste and experiments, medical uses and some foods. The background radiation needs to be subtracted from experiment results on radioactivity.