Space Flashcards
What is weight?
The weight of an object is the force experienced by that object due to the presence of a gravitational field
What is weight mathematically?
Weight is measured in newtons and is the mass of the object multiplied by the acceleration due to gravity
What path does a projectile take on earth?
A parabola
What are the two components of projectile motion and how are they analysed?
Vertical and horizontal components and they are analysed independent of one another
What happens to the x component of velocity throughout projectile motion?
It remains constant
What we’re Galileo three main ideas regarding projectile motion?
- All projectiles follow a parabolic path
- Regardless of mass all objects on earth fall at the same rate
- Horizontal and vertical components of velocity are independent of each other
How did Galileo reach the conclusion that all objects accelerate toward the earth at the same rate and that the time and distance travelled have a square relationship?
By developing an experiment involving rolling balls of different masses down a highly polished ramp to make his comparisons. This would allow him to slow down the motion enough to make more accurate observations of the motion, as compared to just dropping balls to the ground
How did Galileo reach the conclusion that projectiles follow parabolic paths?
By rolling balls off a table at different speeds and mapping the motion
How did Galileo reach the conclusion that projectiles in motion express horizontal and vertical components which are independent of each other?
By coming up with a thought experiment we’re a rider of a horse drops a ball in front of a stationary observer
- according to the rider, the ball drops straight down
- according to the stationary observer, the ball travels with the same horizontal velocity as the rider
What is escape velocity?
The velocity required at a planets surface to completely leave its gravitational field without further energy input.
In terms of kinetic and gravitational potential energy, what does escape velocity represent?
The limiting case where the projectile ‘just reaches infinite displacement’ with zero speed.
In other words, a projectile must have the same amount of kinetic energy as the absolute value of the gravitational potential it has at take off.
That is , kinetic energy + gravitational potential energy is greater than or equal to zero
What did newton use to explain the concept of escape velocity?
Newton came up with a thought experiment where a cannon fires a projectile horizontally on the earths surface with no air resistance.
- at first the projectile would follow a parabolic path and hit the ground some time later
- as speed increases, it will take progressively longer for the projectile to hit the ground, because although gravity is pull the projectile in toward the centre of the earth, the earth is also falling away from the object at the same rate due to its horizontal motion
- increase the speed once more and the projectile with never hit the ground and follow a circular orbit around the earth
- increase it even more, the orbit forms and ellipse
- finally increase more and the projectiles motion becomes hyperbolic and it escapes the earths gravitational field.
What are g forces?
Refers to the force experienced by an astronaut in terms of the earths gravitational field on the surface
What are the two forces acting on an astronaut during launch ?
- the upwards thrust T caused by the rocket
- his/her own weight W acting towards the centre of the earth
By Newton’s second law, what is Thrust equal to?
T= ma + mg
Thus
T-mg = ma
What is thrust equal to in a rocket launch?
The apparent weight of the astronaut, by Newton’s third law
What is the formula of g force?
1 + a/g
Apparent weight/real weight
Why are astronauts put into reclined seats during rocket launch?
They are placed in a position which concentrates the force perpendicular to their long body axis, placing it at their backs, which is good because it prevents black out and red out.
Why do astronauts have specially moulded seats?
Increases the surface of the forces
Why is the term g force used?
It’s easy to relate to and it eases calculations regarding the forces experienced by astronauts during launch
What does the law of conservation of momentum state?
The law of conservation of momentum states that in a closed system, the sum of momenta before a change is equal to the sum of momenta after the change
what is gravitational potential energy?
defined as the work down to move an object from a very large distance away to a specific point in a gravitational field
why is gravitational potential energy always negative?
if an object is lifted above a planets surface, work is being done on that object, giving it energy. if energy is given to the object, its gravitational potential energy must increase. but, at an infinite distance away from the plant, the potential energy is zero. so thus this means that it is a bound system and at the planets surface the GPE of the object will be its lowest possible value
what was the michelson morley experiment and what was its aim?
the michelson morley experiment was designed to calulate the velocity of the earth through the aether, on the grounds that light would travel faster in certain directions and slower in others, due to the relative motion between the earth and aether which could create an Aether wind
what were the materials used in the experiment?
- light source
- half silvered mirror
- two mirrors
- light detector
- liquid mercury platform
what happened during the michelson morley experiment?
a light beam was split by a half-silvered mirror, creating two beams at right angles to eachother, and after letting them travel a short distance, they ere recombined.
there had been no change in the interference pattern observed once the two beams of light had rejoined, even when the apparatus had been rotated 90 degrees. this provided a null result, neither proving or disproving the existence of the aether
why was rotating the MM experiment 90 degrees thourght to change the interference pattern creating by the two beams?
given that the aether wind was travelling in a certain direction, either left or right, up or down, the two scientists decided to rotate the entire apparatus 90 degrees and try the experiment multiple times expecting a difference in interference due to the change of the movement of the light against or with the aether wind
what factors affect the strength of the gravitational force?
- the distance between the two objects, the smaller the distance the greater the force
- both masses involved are proportional to the strength of the gravitational force
on earth, what instances may result in derivation from the normal rate of acceleration of 9.8m/s ?
- due to the earths rotation, the equator bulges out and the poles flatten, causing the poles to be closer to the centre of the earth than the equator. thus, the gravitational force of the earth is stronger at the poles than at the equator
- the strength of the field varies with nearby geography. places where the lithosphere is thick(dense mineral deposists or mountain ranges) experience greater gravitational force compard to places of less dense rock or water
- gravitational force also depends on altitude. high altitudes experience less gravitational force than areas at or below sea level
- spin of the earth causes all objects on the surface to experience a centrifugal force which lowers the value of g.
what is uniform circular motion?
refers to the motion of objects which follow a circular path. it is a very common two dimensional force exhibited in many systems
what are some examples of systems in uniform circular motion?
- the moon revolving around the earth
- artificial satellites
- cars travelling around a corner
describe the velocity and speed of an object in uniform circular motion?
the speed of the object is constant, but because the object in circular motion is always changing direction, the object is constantly accelerating.
describe the force experienced by an object in uniform circular motion
when an object is moving in a circular path uniformly, the acceleration is centre seeking and always acts towards the centre of the circular path. in the same direction of acceleration, an object travelling in a circular path experiences a centripetal force which is also centre seeking
what is the centripetal force acting on a satellite?
the centripetal force is sourced from the gravitaitional force of attraction between it and the earth
define newtons universal law of gravitation
Newton’s law of universal gravitation states that a particle attracts every other particle in the universe using a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
what is the orbital altitude of low earth orbits?
between 250km to 1000km, below the van allen radiation belts
what is the orbital period of low earth orbits ?
90minutes
what is the orbital velocity of a low earth orbit?
8m/s
what are low earth orbits used for?
spying missions performed by the military
surveying weather conditions
mapping ecological threats
what is the orbital altitude of a geostationary orbit?
35800km
what is the orbital period of a geostationary orbit?
one sideral day which is 23.93 hours
what are geostationary satellites?
satellites which orbit the earth directly above the equator at the same speed as the rotation of the earth
what are geostationary satellites used for?
essential to modern communications
what is the source of orbital decay in low earth orbits?
the earths atmosphere extends far into the space. the boundary between the atmosphere and vacuum of space isnt clearly defined, and there are still air particles high above the earths surface
these particles then created drag
what is a gravitational field?
a gravitational field is field created by an object with mass which attracts other masses into the field. it provides a force on objects within it that drags objects into the centre of the field
describe the effect of a gravitational field on an object with and without mass
if a an object with mass has little to no tangential velocity, they will be dragged into the centre of the massive object
if the object has some degree of tangential velocity, they will be pulled into orbit, or they will have their trajectory altered
what were the three ideas Konstantin Tsiolkovsky proposed that contributed to space travel?
- principles behind rocket propulsion, including newtons third law and the conservation of momentum
- using liquid hydrogen and oxygen and fuels
- visualised the idea of multistage rockets
- wrote science fiction
describe Konstantins ideas about the principles regarding rocket propulsion
- he showed how newtons third law and the conservation of momentum can be applied when talking about a rocket launch—> principle that is vital to understanding the operation of a rocket and their functioning
- used newtons ideas about escape velocity to calculate it for earth
- derived the basic rocketry equation including the ‘Tsiolkovsky rocket equation’
describe konstantins ideas about using liquid hydrogen and oxygen as a fuel
proposed the use of liquid fuel propellants, thrust of the rocket could be varied via valves and their use would result in a greater impulse than if solid fuels were used
- also allows g forces experienced by the astronauts to be controlled
- same fuels were utilised in the saturn V rocket that was used in the Apolloe missions to the moon, also used in satellites and space probes, where intermittent firing of rockets is desired rather than a continuous burn as provided by a solid rocket motor
describe Konstantins ideas regarding mulitstage rockets
Konstantin visualised a 20 stage rocket trau that dropped stages as each stage ran out of fuel, to cut weight and improve efficiency
this was vital in high energy launches for manned space missions such as Apollo as well as missions involving high/large payloads
describe Konstantins ideas regarding science fiction
he predicted space stations, space colonies who used biological recycling of good and oxygen
airlocks predicted for moving between a spacecraft and vacuum
what are ensteins two big postulates regarding special relativity?
1) all laws of physics are the same in all intertial reference frames.. no experiments can be conducted to distinguish if you are in motion or stationary
2) the speed of light is constant to all observers, regardless of relative motion of the observer and the light source… ITS A LAW OF NATURE
what is a frame of reference?
the environment( coordinate system or object) from which measurements are taken by an observer
what makes a frame of reference intertial?
inertial reference frames travel at a constant velocity or at rest and experience no accelerations and hence no net forces
what makes a frame of reference non intertial?
any frame of reference that is not accelerating or nor rotating
what was the significance of einsteins postulate that the speed of light is the same in all intertial reference frames?
this means that an observer were to take measurements to identify the speed of light, the value would always be 300000000m/s. but, in some situations newton vector addition will increase the distance the light has to travel, and if measured, with be greater than the speed of light
thus time, length and mass become relative in order for the speed of light to remain constant. this is significant because it demonstrates how objects behave at relativistic speeds
what are the three issues associated with safe re-entry into the earths atmosphere?
- radio blackout
- retarding forces or g forces
- heat generated through atmospheric drag
how does heating come about in re-entry?
the earths atmosphere provides aerodynamic drag on the craft and high temps are developed through friction with the air molecules
the temp is roughly 3000 degrees depending on air flow
how is heating minimised during re-entry?
- high temp resistant shielding, usually carbon or ceramic based which can wishstand the high temps as the craft re enters the earths atmosphere
- the craft re-enters belly first and nose up, shielding much of the heat and creating a shockwave which allows the heat to be dissipated
what is the structure like of a spacecraft which alleviates the heat experienced during re-entry?
- reinforced carbon-carbon composite to protect the nose cone and leading edges of the wings where temps exceed 1300 degrees
- silica tiles on the crafts underside, made from glass fibres containing 90% air. this makes them really light weight an exceptional thermal insulators. these tiles deflect the heat the same way the blunt underside of the craft does as it enters the atmosphere belly first
what happens when the angle of re-entry is too steep?
-the craft descending rate becomes to fast, and the vehicle will encouter the high density atmosphere closer to the earths surface will it retains to much of its high velocity….. high density air provides more drag, decelerating the craft faster leading to more g forces and higher temps, which could be fatal for the occupants in terms of their own health and the health of the vehicle
what happens when the angle of re-entry is too shallow?
the vehicle effectively skims the surface of the atmosphere as it retains to much of its high velocity. it then returns to space
between what range is the optimum angle for re-entry into the earths atmosphere?
5.2
for what values of theta is the angle of re-entry too steep?
greater than 7.2
for what values of theta is the angle of re-entry too shallow?
less than 5.2
what is ionisation blackout?
ionisation blackout out occurs when the molecules in the air surrounding a craft during re-entry become so hot that they ionize. these ionised molecules block radio comminucations with the ground and craft.
although not a direct hazard, in the event of an emergency this circumstance may become quite troublesome if the craft is in jeopardy
how does the vehicle during re-entry succesfully slow down and land on the earths surface?
- deploys a parachute to make a gentle landing
- once the air becomes dense enough, the crafts wings can generate lift, and thus gentling glide to a landing
what is the slingshot effect?
the slingshot effect refers to the use of the motion of a planet to alter the path and speed of an interplanetay spacecraft
what are some other names for the slingshot effect?
gravity assist or gravitational slingshot
how does the slingshot effect work?
- as the space probe enters the field of the planet, its accelerated
- but the field is also moving, and therefore this momentum is given to the space probe, so the probe is effectively dragged by the planet
- but the momentum the probe gained from falling into the field of the planet is lossed as it has to climb up and out of the field as it recedes away
- BUT, the momentum it gained being dragged by the planet is retained, and thus boosts the probes velocity
as well as a boost in velocity, how else can the slingshot effect be used in interplanetary spacetravel?
well bucko, if a probe wants to reach the outer planets, its gonna have to travel away from the sun and its immense gravitational field. as such, the probes trajectory with eventually be curved into an orbital path. hence, the slingshot effect may be used to alter a probes trajectory away from the sun
what are some advantages of the slingshot effect?
- the slingshot effect saves time, fuel and expense
- the probes’ can reach much higher speeds than if they used their own fuel
what are the disadvantages of the slingshot effect?
- Must wait until planets are in the right location for the right trajectory, sometimes this takes many years
- Space probes must be careful not to get too close to the planet, as their upper atmosphere can cause atmospheric drag
what is the aether model for the transmission of light?
the luminferous aether was belived to be the medium through which light must travel.
what are some of the properties of the aether and why must the aether have these properties?
- highly elastic: in order for light to trave extreme distances, the medium through which it must travel must be highly elastic as to ensure energy is not lossed to the particles of the medium
- has an extremely low density: this is because it cannot be weighed or felt by objects which move through it
- be perfectly and utterly transparent: since it cannot be seen
- has no mass
what are some features of the aether?
- filled all space: this is because light can travel anywhere
- it must be stationary in space: this is because light travelled in straight lines, and so if the medium through which it is travelling is moving, this would alter the path of light travelling through it
- permeate all matter: since light can travel through matter(water, glass, perspex etc.)
why is newtons law of gravitation important in understanding and calculating the motion of satellites around large bodies?
- the law can be equated with the equation for centripetal force to identify an expression the orbital velocity of a satellite. this is especially useful because it shows that the mass of the satellite does not effect its velocity. its also important because for any man made object going into orbit, knowing its orbital velocity is very useful
- newtons law can also be used to derive keplers of periods, an integral tool in understanding the motion of satellites in a given system.
in theory, what is measurement?
the process of comparing some quantity, such as length, mass or time to a selected standard and expressing that measured quantity as some factor of that standard. it then follows that all measured quantities are relative quantites
how was the metre originally measured?
the metre was originally defined as one ten millionth of the distance between the equator and the North Pole along the meridian passing through Paris. this distance was then communicated between two lines on a particular model platinum bar. copies were made and sent throughout the world
what was wrong with using a platinum bar to define the metre?
defining the metre to an actual physical object was problematic, as temp, along with other factors (e.g. the bar could be stolen, lost or damaged) could corrupt the definition of the metre
how is the metre measurement now defined as?
the metre has now been defined in terms of time and velocity, and it is now the distance travelled by light emitted from the element krypton 86 in a vacuum in the fraction 1/299,792,458 of a second
whats amazing about the new measurement for the metre?
because in terms of special relativity the speed of light is forever constant in any inertial reference frame, this standard will forever remain the same and impeccably accurate. physical standard including those planting bars have now been placed in the archives
what is the relativity of simultaneity?
refers to Einsteins contention that if an observer sees two events to be simultaneous, than any other observer, in a different frame of reference, may not judge them to be simultaneous
what thought experiment can be used to explore the relativity of simultaneity?
consider a train moving at some considerable portion of c. in the middle of the carriage is a light source, and at either end of the carriage are doors with light sensors that are an equidistance away from the light.
in the relativity of simultaneity thought experiment, what does the person inside the train observe?
when the light in the carriage is turned on, light travels to the doors, and the doors open at the same time that the light sensor detects the light. for the person on the train, both doors open at the same time because the distance from the light source to the two doors are equal
in the relativity of simultaneity thought experiment, what does the person outside the train see?
the person outside the train sees the doors opening as non- simultaneous
-when the light turns on, the distance to each door is equal. but the train, from the persons perspective is moving. this means from their perspective the light reaches the rear door first
since the train is moving forwards, the front of the train is moving away from the point where the light had originally been sourced
what is time dilation?
time dilation Is where the time in a ‘moving’ frame appears to go slower relative to a ‘stationary’ observer (from their point of view). this means that moving clocks run more slowly. observers in different frames in relative motion will always judge the time taken to be longer
what is length contraction?
length contraction is where the length of a moving rod appears to be contract in the direction of motion relative to a stationary observer
what is mass dilation?
mass dilation is the increase of mass of an object as it approaches the speed of light. at relativistic speeds this happens asymptotically, and prevents any object from exceeding the speed of light because greater and greater mass requires greater and greater force to accelerate the object
how did Einstein explain mass dilation and how did he use this to come up with his most famous equation?
Einstein concluded that the additional energy supplied to the object is being converted into extra mass. this results in a newer definition of the energy of an object:
E= 1/2mv^2 + mc^2
where 1/2mv^2 is the kinetic energy of the object
but, when an object is at rest, it has zero velocity, and hence it has zero kinetic energy. hence, the residual energy represents the mass-equivalent energy of the object. thus the famous equation E = mc^2
how has Einsteins most famous equation impacted on science?
knowledge of mass energy equivalence eventually led to the development of nuclear power and weapons, as well as being an internal part of our understanding of quantum physics
what implications does mass dilation have for space travel?
mass accumilation (which decreases the aceleration of a given thurst) means that accelerations beyond 0.9c will be impractical: greater and greater forces and energy input only account for marginal increases
this means that high speeds, which are necessary for humans in travelling to distant worlds in a reasonable time frame requires stupendous amounts of energy which is prohibitive and out of reach
what implications does time dilation have for space travel?
time dilation means that astronauts in relatavitstic spacecraft will age slower than people back on earth, which means that they can essentially live longer during relatavistic flight compared to a stationary observer, who will pass away well before the astronaut
time dilation also makes long space journeys practical as they become possible to achieve within a lifetime. but because of the immense amount of fuel and energy and hence costs to reach these speeds, this situation is currently impractical
what implications does length contraction have on space travel?
trips on relatavistic spacecraft will appear to cover less distance to observers in the spacecraft. this distance to the distant location appears to shorten, and thus the journey will appear to take less time
this effect only takes form when close to the speed of light, which requires immense amount of energy expenditure as discussed above and hence prohibitive costs, making the prospect impractical and unlikely
what are two observations that support einsteins theory of special relativity?
Atomic clocks and the Hafele Keating Experiment
Muons in cosmic rays
whats a muon?
a muon is a particle similar to an electron, but heavier created in the upper atmosphere
how do muons support einsteins theory of special relativity?
muons have a half life of around 2 microseconds, but they are still detectable from the earths surface.
when they travel at 0.996c they have a half life of roughtly 60microseconds, which supports einsteins theory. this means that as the muons travel at the speed of light, the time and length of the journey has contracted for the muon, allowing it to travel to the earths surface in its lifetime
how do atomic clocks, Hafele-keating experiment, support einsteins theory of special relativity?
-experiment involved taking 4 scynchronised clocks, with two at the ground and two others put in different commercial planes sent flying into opposite directions
when later compared after circumnavigating the world, both the clocks showed less time had passed than the clocks on the ground, with differences of around 50nanoseconds in an easterly direction, and around 270nanoseconds in a westerly direction
this suggested that time dilates at relatavistic speeds
what is the relationship between theory and evidence?
there is a direct relationship between theory and evidence supporting it
no hypothesis can be considered a theory until there is evidence confirming that the hypothesis is correct
so, at the time einstein had devised, what were his predictions regarding special relativity?
einsteins conclusions were merely predictions of what would happen at relativistic speeds and nothing more at the time he devised them, and his ideas only become theory later after evidence confirmed his famous postulates
