let's see how quickly we can cover everything you need to know for AQA gcsc physics paper 2 this is good for higher and Foundation Tier double combined Trilogy and triple or separate physics that's topics 5 to 7 that's forces waves and magnetism finishing off with p8 space which is only for triple I'll tell you when other things are just for triple too we're going to be gunning it so pause the video if you need a bit more time to get your head around something you see let's go a force is any push or pull forces can be contact forces that's when objects are physically touching like when you push a door or they can be non- contct like magnetism electrostatic forces and gravity This Is A New Concept in GCS physics and shocker it's a silly one because even contact forces are due to the electrostatic repulsion between electrons in your skin and the door for example but whatever technically pushing a door involves a normal contact force while other contact forces could be friction air resistance and tension the important thing is that we can represent forces with vectors that is an arrow that shows the dire and magnitude of the force the magnitude is the size of the force and that's indicated by the length of the arrow if two forces act on an object there is a resultant Force we find this by technically adding the vectors however if they're going in opposite directions one must be negative so in this case the resultant force would be 3 Newtons to the right and that's positive if we've decided that positive is in the right direction if vectors are at right angles to each other you use Pythagoras to find the resultant this works because you can make a triangle by moving one of the forces you could also be expected to use trig that's socker TOA to find either one of these angles chance of is going to be tan you use if any if forces are balanced that is they add up to zero that means that the object will not accelerate it won't change velocity no that doesn't necessarily mean it's not moving it just stays at a constant velocity and that could be 0 m/ second of course this is Newton's first law of motion by the way more on those in a bit if a measurement or quantity just has magnitude but no direction it's not a Vector but it's called a scalar instead here are some examples of both note that displacement is distance traveled with a direction while similarly velocity is the vector form of speed weight is another name for the force due to gravity that acts on an object it's calculated by multiplying the mass in kilog by gravitational field strength or G which here on Earth is 9.8 Newtons per kilogram sometimes we just round that to 10 though you'll be told which to use in a question that means that 1 kgam of Mass on Earth has a weight of 10 Newtons now if you hold an object up with your hand you must be pushing up with a force that is equal to its weight in order for the forces to be balanced and so it doesn't accelerate however that means that if you lift it upwards at a constant speed that's also true that's something that people often forget to lift something at a constant speed you must be lifting with a force that's the same as the weight we can therefore then calculate the energy that is used to lift this object using the equation for work done that's work done equals force time distance moved work done is just is a fancy term for energy transferred by a force this equation is true for any situation but in this case the force is the weight and the distance is the height so we could say the gain in energy is equal to mass * G * H does that look familiar it should because that's the exact same equation for calculating gravitational potential energy that's GP gained to be precise forces can also deform an object if you pull on a spring that is fixed at one end it will stretch or extend hooks law states that FAL K that's Force equals spring constant sometimes called stiffness times extension the unit for spring constant is Newtons per meter this works for any object that stretches elastically that is returns to its original shape once the force is removed it can also be true if an object is compressed instead we can see that as K is a constant force and extension are directly proportional that means whatever happens to one happens to the other double the force double the extension you can hang varying masses off a spring and to the extension and you'll end up with a straight line that goes through the origin 0 0 and that proves this directly proportional relationship if you carry out this experiment just make sure your ruler zero Mark is lined up with the bottom of the spring that way you can be sure you're only measuring extension rather than the length of the whole spring that would introduce a systematic error if you did that by mistake also make sure you're at ey level with the bottom of the spring when measuring against the ruler to avoid Parallax error and that is a random error rather than a systematic error the energy stored in the spring is equal to half k e^ s something was attached to the spring and you let go the object would gain the same amount of kinetic energy at least in an ideal or closed system that is no energy is lost of the surroundings due to heat for example just for Triple A Moment is a turning Force for example what you do with a spanner this is equal to force times distance to the pivot so the unit just ends up being newton meters note that this looks similar to the work done equation but this force and distance here are perpendic icular to each other rather than parallel similarly to just normal forces if the moments turning clockwise are equal or balanced with the moments turning anticlockwise the object will not turn that is if it wasn't turning to begin with we can call this the principle of Moments by the way an application of moments is Gears a small gear can turn a large gear in order to increase the moment produced you can think of pressure as being how concentrated a forces is the equation is pressure is equal to force divided by area so the unit for pressure is Newtons per M squ we can also call this unit pascals or PA for short you probably know the deeper you go underwater the greater the pressure and this is due to the weight of the water above your head pushing down on you we can calculate this pressure using p equal H row that's just a Greek letter time g h being height of the water column above you basically depth times density times gravitational field strength the density of water is 1,000 kg per M cubed for gas pressure in paper to all you need to know is that it's due to the collisions of the gas particles with Sur surfaces and you can hopefully remember from paper one that you can increase this by adding more gas reducing the volume or raising the temperature which makes the particles move faster all three of these result in the collisions occurring more frequently while increasing the temperature also means that the particles have more kinetic energy so they collide with the walls with more momentum therefore exerting a greater force more momentum in a bit the higher your altitude the less dense the atmosphere becomes due to there being fewer particles in any given volume hence pressure also decreases back to double speed and velocity are measured in me/ second while velocity also has Direction so it could be positive or negative or up and down left and right here is some typical speeds for when you're traveling of course speed and velocity are calculated by distance or displacement over time if you have a distance time graph the gradient of the graph gives you the speed or velocity if it's a curve just draw a tangent at the point you need to and find its gradient a speed or velocity time graph can give you even more information this time the gradient gives you change in speed divided by time which is acceler ation here's the equation two the unit of acceleration is m/s squared and it tells you how quickly speed is changing if it's a negative gradient heading to zero that means the object is decelerating slowing down however this graph can also go into negative values for example when a ball is thrown upward and comes back down in that case the velocity starts positive and fast but decreases to zero when it reaches the top where it then turns around so the velocity becomes more negative as it falls incidentally this graph has a constant negative gradient where gravity is accelerating it downwards at a constant rate even though its direction changes what you find is that for any object that's falling its acceleration is 9.8 m/s squared the same as gravitational field strength because they are the same thing a velocity time graph can also give you the distance traveled you get that by calculating the area under the graph any area under 0 m/s counts as negative displacement by the way thus why the area of both these triangles in this graph adds up to zero that makes sense though doesn't it seeing that it's gone back from whence it came I.E your hand suat or Newton's equations of motion are a way of predicting what an object will do if it's accelerating s is displacement U is initial velocity V is final velocity a is acceleration and T is time however AQA only give you one of these equations in the formula sheet and so that's really the only one that you will be expected to use U is zero if it starts at rest V equals z if an object is moving to begin with but then decelerates to a standstill for objects falling a is the same as G that's 9.8 m/s squared for any question involving one of these equations you write down your variables put a question mark next to what you're trying to find and put the values next to the other three that you've been given you can ignore the fifth unused variable depending on what data you're given you pick the correct equation with the four variables in rearrange it if necessary then just plug in your numbers we already know that Newton's first law is this when there's no no resultant Force an object's motion is constant in other words no change in velocity that could be because there's no forces acting or the forces are balanced by the way inertia is the term we use to describe the tendency for an object's motion to stay constant unless acted on by a resultant Force Newton's Second Law involves unbalanced forces that is there is a resultant Force this is equal to ma masstimes acceleration that's all Newton's second law is FAL ma only one of these can be true in any situation there's either no resultant force or there is we can prove Newton's second law by doing a practical we use a trolley on a track being pulled by the weight of masses hanging over a pulley in the end we can use light Gates photo gates to measure the acceleration between two points then change the weight on the string just remember that whatever Mass you take off the hanger must go on the trolley itself as the force is accelerating both the trolley and the masses themselves we draw a graph of force against acceleration and it should be a straight line through the origin proving the proportional relationship between F and a the gradient should give you the total mass of the trolley and slotted masses Newton's third law however is always true and this is the one that people get confused about understandably for every action or Force there is an equal an opposite reaction force but this is not referring to balanced forces it's all about perspective when we think about the first two laws we only really consider the object itself for example the force pulling downwards on the ball is its weight even if if there is air resistance there's a resultant Force downwards however if you zoom out and think about the Earth too well we know that the Earth is pulling down the ball but Newton's third law says the complete opposite is true as well the ball is also pulling the Earth up now the Earth is so massive that it doesn't really have an effect but it's still true nevertheless another example if we have two ice skaters if the guy skater pushes on the girl skater there's an equal and opposite reaction Force pushing back on him too that's why they both move away from where they were the overall stopping distance for a car is a result of the thinking distance that's how far you go before you react to seeing the Bunny and the braking distance after you slammed on the brakes if you double your speed you double your thinking distance because you travel twice as far in the time it takes for you to react makes sense however doubling your speed quadruples your braking distance because your car needs to lose all of its kinetic energy which is equal to half MV squared well that means that if you double the V * 2^ 2 is Time 4 if you triple your speed kinetic energy goes up by times 9 so that means so does your braking distance other factors that affect thinking distance are distractions alcohol drugs whereas braking distance can be affected by the condition of your brakes the tires the road the weather Etc the faster you go the more momentum you also have momentum is similar to inertia you can think of it as being a measure of how hard it is to get something to stop here's the equation momentum is equal to mass times velocity the unit therefore is kilogram m/ second momentum is a vector which means you have negative momentum if your velocity is negative in a collision kinetic energy isn't always conserved but total momentum always is that means whatever the total momentum of the objects was before there must be the same total momentum afterwards as well calculations on this can be tricky but you just have to be careful with your pluses and minuses you're right down M1 U1 if there's just one object moving to begin with remember U from suat we can use it here too and on M2 U2 if there's a second object moving too this then is the total momentum before the Collision before the event this could also be zero if nothing's moving to begin with say a cannon about to fire then all we have to say is that this is equal to the total momentum afterwards M1 V1 for one object plus M2 V2 if there's a second object moving too if they' coupled together we just say m * V where m is the total mass of the two then all you have to do is pop your numbers in making sure that everything traveling to the left say has a negative velocity and you'll be left with one unknown rearrange to find it you get your answer incidentally in the case of the Cannon as there's zero total momentum before the same must be true after two even though the cannon ball is moving that must mean the cannon has the same momentum but in the opposite direction so they still add up to zero this is an example of recoil just for triple force and momentum are closely linked Newton's second law says that F equal ma but we also know that a is equal to Delta V / T so actually it's also true that force is equal to change in momentum over time or we can say the rate of change of momentum the shorter the time taken for momentum to change the bigger the force needed or felt that's why we use seat belts airbags and crumble zones in cars your change in momentum is the same when you use them but they increase the time taken for this to happen so a smaller force is felt you're more likely to survive it's just two ways of looking at forces the bigger the force the faster the acceleration or deceleration and so that also means the fast the momentum changes too waves next all waves transfer energy without transferring matter oscillations or vibrations are pass along instead of the particles themselves longitudinal waves are those in which the direction of the oscillations is parallel to the direction of energy transfer that is the direction the wave is going examples of these are sound waves and seismic p waves P stands for primary because they're fast in these waves particles Bunch up we call those compressions and when they're spread out we call those rare refractions transverse waves are those in which the direction of oscillations is perpendicular to the direction of energy transfer they wiggle side to side or up and down examples are waves on the surface of water seismic S waves secondary they're slower than p waves they produce earthquake after shocks and light and also every other em electromagnetic wave too we can represent any wave including longitude wav like this we call this a waveform displacement is up the y- AIS basically just how far the particles have oscillated from their original position and it can be either distance or time on the x-axis the peak of a wave is called the amplitude the maximum displacement from equilibrium if it's distance on the x-axis one complete wave here gives you the wavelength we give this the symbol Lambda for short but it's measured in meters if there time on the x-axis instead one complete wave gives you the time period capital T for short this is the time it takes for one complete wave to pass measured in seconds frequency on the other hand is how many waves pass a point every second and the unit is Hertz so frequency and time period are the opposite in fact they're reciprocals of each other so we can say frequency is equal to 1 over time period f = 1 /t you can often be asked to find frequency from a waveform like this measure the time period Then do one divided by that easy the wave equation is this V equal f l that's wave speed equals frequency time wavelength a ripple tank will tell you what frequency is made you can measure the distance between 10 Peaks then divide by 10 to get the wavelength say then just use the wave equation to get the speed of the wave you could also just time how long it takes for a ripple in a tray of water to travel the length of the tray 10 times then just do total distance of other by time to get speed instead the speed of sound waves can be measured by attaching a microphone up to oscilloscope for example if you clap once next to the microphone the sound can Echo off a wall and known distance away and it comes back to the microphone then you can just use the oscilloscope to measure the time it took to travel then do total distance divided by time again just for triple sound waves cause the a drum to vibrate which in turn is converted into a signal that travels to your brain the human ear can hear frequencies between 20 Herz and 20 khz 20,000 HZ any frequency Above This is called ultrasound whenever Sound reaches a boundary between two different mediums materials some of it goes through we say it's transmitted while some is reflected this is the case when we emit ultrasound into a person's body and a computer can time how long it takes to return off different layers allowing it to build up an image of what's inside this allows us to scan babies safely we can also time sound waves in water to build up a picture of what's under a boat or around a submarine this is called sonar we've mentioned seismic waves already but you also need to know that while the longitudinal p waves can travel through liquids transverse s waves cannot that's how we've come to believe that the Earth has a molten core there's no Aftershock felt when an earthquake happens on the other side of the earth which implies that there must be a liquid Center when waves reflect off a smooth surface we say that's specular reflection that just means not scattered like a mirror the angle of incidence will be equal to the angle of reflection all angles are measured from the normal which is a line we draw perpendicular to the surface if light is scattered off a rough surface we call this diffuse reflection instead em or electromagnetic waves are for everybody they're special because they don't need a medium to travel through they're the only waves that can travel through the vacuum of space there are a range of wavelengths in the EM spectrum which we split up into these sections radio waves microwaves infrared radiation visible light ultraviolet xrays gamma rays if you you haven't heard the original version It's a certified Banger Link in description EM waves are produced when electrons lose energy they lose the energy as an EM wave the higher the frequency the more energy the wave carries and the shorter the wavelength The Only Exception are gamma rays which are actually emitted by nuclei instead that means lots more energy is involved that's why they're dangerous they are all however absorbed by electrons this allows our retina to detect light for example phone antennas to receive radio signals and your face to absorb infed from the Sun and feel heat UV X-rays and gamma rays carry so much energy though that they can cause electrons to leave their atoms the atoms have been ionized that can be dangerous if absorbed by DNA in cells as this can cause mutations that can lead to cancer while some Ian waves can be dangerous we use all parts of the spectrum for communications cooking heating Imaging Medical Treatments and more when light waves move from one medium to another say from Air to Glass they change speed in this case the w wave slows down and the wavelength also decreases instead of drawing the wave fronts from above like what you see above water we can just draw a ray to show the direction that the light is moving in that's a lot easier a change in medium also results in a change in Direction This is called refraction that is if it's at an angle to the normal the line we draw perpendicular to the surface you can think of light always wanting to get away from the normal but never write that in the exam if light slows down it moves closer to the normal so that means that the angle of refraction is smaller than the angle of incidence that's the angle that it hits the surface at now all of these angles are measured from the normal that means you must have your protractor with the zero on the normal never have it flat on the surface it's always perpendicular to the surface the rest of waves is triple only so skip to magnetism if you're double lenses oh boy here we go okay lenses are curved blocks of glass also you have them in your eyes they use refraction to make rays of light converge meet or diverge spread out a convex lens can make Rays converge this is the symbol we use to represent it if Rays enter parallel to what we call the principal axis for example the light from an object very far away the lens will make the Rays converge at this point here this is called the principal Focus the distance from the center of the lens is called the focal length this doesn't change for a lens and we can draw it on both sides and you'll see why in a bit however light doesn't usually come from object objects infinitely far away but from objects a little bit nearer the object could be anything but we often represent it with just an arrow convex lens can then project an image using the light that comes from the object but we only consider the light coming from the top of the object and we can do that by drawing two rays one always go straight through the center of the lens and one goes parallel into the lens then through the principal Focus where these two rays meet is where the image is formed that's where you want your projector screen or retina or camera sensor to be in order to get a clear image formed you'll also notice that the image is smaller than the object so we say it's diminished it's also upside down so we say it's inverted things get a bit trickier when the object is very close to the lens now the Rays don't meet the image can't be projected however if we extrapolate the two rays back behind the lens they do meet we can draw the image here and we can say that it's magnified it's upright but it's virtual that means that it can't be projected it's no longer a real image like we had before this would be what a magnifying glass does for example your eye can deal with this diverging light accordingly to make it focus on your retina but that means that you see this magnified virtual image so things appear bigger concave lenses always diverge like Rays they always produce a virtual image with these our line parallel in goes back through the other principal Focus behind the lens where it meets the other Ray is where the virtual image is this image is also diminished and upright as you can see the magnification of a lens is just the ratio of image height to object height a magnification greater than one means the image is bigger than the object less than one it's diminished it's smaller than the object what we perceive as color is a result of different wavelengths of light being emitted by a source or reflected by an object that are then absorbed by the cells in our retina most objects will absorb some wavelengths of light while reflect others for example chlorophyll in Plants absorbs longer red wavelengths of Light which is why leaves appear green it reflects those shorter wavelengths this ball looks blue in sunlight because it reflects the blue wavelengths of light shine just red light on it though and it will appear black as that red light will be absorbed no light will be reflected no idea whether this is gcsc but here we go a black body is an object that perfectly absorbs and emits all wave lengths of radiation while there's no such thing in reality it's a useful concept that we can apply to some object like stars or planets if a body or object absorbs radiation at a greater rate than it's emitting it its temperature will increase but if the temperature increases that also means that it starts emitting radiation at a greater rate too magnetism and electromagnetism a permanent magnet is a metal in which the molecules are permanently aligned in such a way that they produce a magnetic field which can exert a force on particles in other objects and also electrons we give the two ends of a magnet the names North and South Pole short for North facing and south facing poles because that's the way they would point to line up with the Earth's magnetic field so if we made it float you can use iron filings or mini compasses placed around a magnet to visualize its magnetic field magnetic field lines are always complete Loops even though we don't draw them inside the magnet and they never touch these ones going out the ends here will eventually loop back around if we carried on drawing them the direction of magnetic field lines is always from North Pole to South Pole and in jued magnet is a material usually a metal whose particles align temporarily when placed in a magnetic field so it makes its own magnetic field hence why an iron nail can be attracted to both the North or South Pole of a permanent magnet we say iron is magnetic but it is not a magnet Cobalt and nickel are also magnetic copper and aluminium for example are not bring two permanent magnets together and they will attract if opposite poles are facing and they repel if like poles are facing a current flowing through a wire will produce its own magnetic field we draw the field lines as concentric circles around it using our right hand to help us remember which way the field goes we use the letter B as a Shand for a magnetic field by the way as well as in the equation coming up the motor effect is when such a wire is in another magnetic field and it will experience a force the equation is f Bill where f is force I is current in amps L is length of the wire in the magnetic field and B is the magnetic flux density essentially the magnetic field strength this is measured in Tesla note that this equation only works as it is if the current and magnetic field lines are perpendicular to each other but maybe it is worth remembering that if the wire is parallel to the field lines it will experience no Force to find out the direction of the force however on The Wire we use Fleming's left hand rule your thumb is force first finger is field middle finger is current make a juny gun with them where they're all perpendic ular and Bam freeze FBI just twist your wrist to line up your fingers with the current and the field always North Pole to South Pole and the way that your thumb is pointing is the direction of the force on the wire in this case upwards to measure the size of the force in reality we can put the magnet on a balance due to Newton's third law the magnet will also be pushed down with the same Force calculate the force from the fake mass measured use an ameter to get the current and a ruler to measure the length of the wire and boom you can calculate the magnetic flux density between the poles of your magnet electric motors of course employ the motor effect by using a coil of wire that experiences opposite forces on both sides causing it to turn however the current must be reversed every half a turn otherwise it would just stop at the vertical position in this case so that's why we have what we call a split ring commutator to reverse the current every half a turn to make a motor turn faster you can increase the current use a stronger Magnet or add more turns to the coil so there's is a greater length of wire ultimately experiencing the force a loudspeaker is in essence just a motor that goes back and for instead of round and round the varying current due to the signal from the music play essay will cause the coil to vibrate back and forth and that's attached to the speaker cone which then produces sound waves in the air double people you're actually done but don't forget to leave a like before you leave here a magnet will cause a current carrying wire to move but the opposite is also true a wire that's moved through a magnetic field will result in a current being induced in it the electrons will move to be more precise we should say a potential is induced in it essentially voltage this can be called the Dynamo or generator effect a generator itself looks like a motor you turn the coil and a potential will be induced in the coil this is basically how power stations work the steam made from burning fuels or nuclear fision turns the turbine which turns this coil as you can see we don't need a split ring commutator it still works all that it means is that it's an alternating PD that's produced or alternating current AC to increase the output of a Dynamo or generator just turn it faster or similar to a motor add more turns to the coil or use a stronger magnet I say turn it faster but it's not easy you see the current induced in the coil also produces its own magnetic field and this opposes the turning that led to it being produced to begin with so that's why it requires energy to keep it turning and that makes sense you can't just start it turning and then it just carry on otherwise that would mean you'd be getting energy for nothing but in other words this means that induced currents or potentials don't like being made some dynamos have a split ring commutator or circuitry such that they produce DC instead of AC it will be lumpy DC though over my lifetime that name has been used for both I guess but aqaa generators produce AC while a Dynamo produces DC so let's go with that similar to a loudspeaker being a back and for motor a microphone is a back and forth generator sound waves move the diaphragm back and forth which is attach to a coil that moves back and forth around a magnet and that then induces a potential in the coil that signal then travels through the wires to the phone recorder or whatever Transformers are used in the National Grid to change the voltage at which the electricity is transmitted through the overhead cables the current from a power station is so high that too much energy would be lost due to the resistance in the cables if it just went straight into them therefore A Step up Transformer increases the voltage before it enters the grid this then reduces the current so less energy is lost due to heating the reason one goes up while the other one goes down is because electrical power is equal to voltage or PD * current V * I in an Ideal World the power in and out of a transformer should be the same that would mean that it's 100% efficient so V and I are inversely proportional we can therefore say that V * I for the primary coil is equal to V * I for the secondary coil this is the basic makeup of a transformer the primary coil is connected to the power station in this case the secondary coil is connected to the overhead cables there are more turns on the secondary coil which means it's a Step up Transformer the voltage will increase the current will decrease the cars are wrapped around a soft iron core get this into your head right now though there is or should be no electricity or current in the core instead the electricity is wirelessly transmitted from one coil to the other how is this well it's because the alternating current in the primary coil produces its own magnetic field and the iron core acts like a guide for it we use iron by the way as it's easily magnetized and demagnetized it works well as a guide this magnetic field then induces a voltage and current in the secondary coil in order for a current to be induced though a wire must experience a change in the magnetic field which is why we must use AC if we use DC in the primary call it would make a magnetic field but it would be static which cannot induce a current in the secondary coil the ratio of turns in the coils is equal to the ratio of the voltages if the secondary coil has double the turns it has double the voltage and therefore half the current so we can say NP / NS equals VP / vs you can also flip the whole thing when it comes to rearranging it to find vs or NS A Step Down Transformer at the other end of the cables steps the voltage back down to a safer PD of 230 volts which means it must have fewer turns on the secondary coil finally space lots of grand ideas here our solar system consists of the sun with the eight planets orbiting it with an asteroid belt as well between Mars and Jupiter and other dwarf planets too poor old Pluto our moon and other planets moons are natural satellites our solar system is one of many found in our galaxy which we call the Milky Way it's believed that stars are the result of dust and gas particles in clouds we call such a cloud a nebula being attracted to each other due to gravity the cloud becomes hotter and more dense until Fusion starts to occur a star will remain stable so long as the outward pressure from Fusion and the force of gravity pulling inward remain balanced we say it's in the main sequence stage of its life when a star dies the outward pressure increases which causes it to expand turning it into a red giant if it's a star a similar size to our sun or a super red giant for stars much bigger than our sun a red giant will then collapse once all the fuel for Fusion has run out leaving a white dwarf and then a black dwarf once it's cooled a super red giant explodes we say it's gone Supernova leaving a very dense neutron star at the center or an even more dense body that causes a black hole there the outer layers of the Supernova move away forming new nebula from which new stars could be made nuclei fused together to make heavier elements some of these could only be made as a result of the huge amount of energy released from a supernova our moon is a natural satellite while Elon makes artificial satellites in both cases they orbit the earth some satellites orbit in a circle around the earth Like geostationary Satellites these sit above the same spot above the equator and they're used for GPS and communication they move at a constant speed yet their direction is constantly changing so technically their velocity is constantly changing which means that they're accelerating towards the Earth they just don't get any closer as they're going too fast any force that results in circular the motion is called the centripetal force and that always acts towards the center of its orbit we can draw the velocity at any point as a tangent so if the Earth suddenly disappeared that's where this satellite would fly off that means that centripetal force and velocity are always at right angles to each other they're perpendicular other satellites travel in elliptical orbits and they're used for reconnaissance and weather for example the closer they get to the Earth the faster they move and vice versa we have a good idea of what wavelengths of light are emitted from Stars however when we look at distant stars and galaxies these wavelengths appear longer they're shifted towards the red end of the spectrum the light has been red shifted much like when the pitch of an ambulance siren drops when it's moving away from you like this shows the galaxies must be moving away from us and this is the case in every direction we look not only that the light from more distant galaxies is even more red shifted suggesting they're moving faster away from us receding faster we say at a faster rate this implies that if we go back in time all of these galaxies appear to have originated from the same point in space this is therefore used as evidence for the Big Bang Theory and that the observable universe is still expanding the other piece of evidence for it is cmbr Cosmic microwave background radiation outer space might look dark but we can detect microwave radiation being emitted from very far away from all Direction this could be emitted as a result of matter still cooling down so it seems we're looking at the edge of the Big Bang which is essentially still going so that's it I hope you found this helpful leave a like if you did pop any questions or comments below and hey this is your last science exam so after you've done it come back here and tell us how you got on we'd love to know