9.2 Space

Question	Answer
weight	the force on an object due to a gravitational field F = mg
gravitational potential energy	the work done to move an object from a very large distance away to a point in a gravitational field.
escape velocity	the velocity at which an object on the surface of a body must be propelled in order to not return to that body under the influence of their mutual gravitational attraction.
effect of earth's orbital motion on the launch of a rocket	launched in an eastward direction to take advantage of rotational speed of the earth, thus gaining an additional velocity during take-off without requiring extra fuel
effects of large g forces on astronauts	positive F = drains blood from brain, unconsciousness or black out negative F = blood rushes to brain, excessive bleeding & brain damage
factors helping astronauts survive large g forces	lie down (forces act along backup-to-front axis); special cushions; wear 'g suits' (apply pressure to lower parts of body, preventing blood from being pulled away from the brain)
UCM for satellites orbiting earth	Centripetal force is provided by the gravitational attraction force. As a satellite orbits the earth, it is pulled downwards by the earth's gravitational field. Its linear orbital velocity keeps it from fallng, since at the same time it is falling it is moving away from the earth (centripetal force), resulting in a circular path.
low earth orbit advantages	avoids atmospheric drag, avoids Van Allen radiation belts, provide scans of different areas of the earth, closer view of surface, cheap & easy to launch
low earth orbit disadvantages	orbital decay, orbital paths have to be controlled to avoid interference, severely affected by radiation belts
geostationary orbits advantages	easy to track (stays in one position at all times), don't experience orbital decay
geostationary orbits disadvantages	delay in information transmission, limited view of earth, launching process difficult & expensive, damage from cosmic rays due to high altitude
orbital velocity	orbital speed of a body in a gravitational field
Kepler's third law of periods	the square of the period of a planet's motion about the sun is proportional to the cube of the mean distance of the planet from the sun. r^3/T^2 = GM/4pi^2 if objects act as satellites around a primary, then all satellites which orbit the same primary are in the same ratio. r^3/T^2 = k
orbital decay	friction is generated when a low orbit satellites moves, which slows down its orbital velocity causing it to drop to a lower orbit. It is now in a denser part of the atmosphere, where an even greater resistive force acts on it, so it slows down at a faster rate and continues to move into a lower orbit. It is usually burnt up in the denser atmosphere due to heat caused by air friction.
issues associated with re-entry	1. vaporisation by heat generated by atmospheric friction (prevented by heat shields) 2. ionisation blackout (loss in radio communications)
optimum angle for safe re-entry + consequences of too big/small	5.2 - 7.2 degrees too big: upward resistive force will be too large, & astronauts won't be able to withstand g forces too small: bounce off the atmosphere and back into space
the slingshot effect	the increase in velocity given to a spacecraft because it enters the gravitational field of a planet as it flies past it
features of the aether model of light	1. fill space 2. be stationary in space 3. be transparent 4. permeate all matter 5. have an extremely low density 6. have a great elasticity
Michelson-Morley experiment	to determine the velocity of the earth relative to the aether. interferometer mounted on a stone floating in mercury, beam of light directed at a mirror, beam split and sent in 2 directions and the light rays reflected from mirrors. they thought that when thr interferometer was rotated thr interference pattern would change, but there was no change observed.
inertial frame of reference	observer is experiencing no net force & is moving at a constant or zero velocity
non-inertial frame of reference	observer is accelerating
principle of relativity	1. all motion is relative 2. all inertial frames of reference are equivalent 3. there is no such thing as an absolute frame of reference
Einstein's thought experiment	"if I was sitting in a train travelling at c and hold a mirror in front of me, will I see my my reflection?" yes - light travels at its normal speed relative to the train. he concluded that it is not the speed of light that is changing, but time.
1 metre	the length of the path travelled by light in a vacuum during the time interval of 1/4587922991 ths of a second
relativity of simultaneity	if an observer sees 2 events to be simultaneous, another observer in a different frame of reference may not judge them to be simultaneous
equivalence between mass and energy	E = mc^2 energy and mass are no longer independent; mass can be created by sacrificing energy; energy can be created by destroying mass
length contraction	the length of an object measured within its frame of reference is its proper length, but observers in different frames of reference will judge the observed length to be contracted Lv < Lo
time dilation	the time taken for an event to occur in its rest frame is called proper time, but observers in different FOR will judge the observed time to be longer tv > to
mass dilation	the mass of a moving object increases as velocity increases. this effect is only noticeable at relativistic speeds
implications of special relativity for space travel	amount of energy to accelerate beyond 0.9c is prohibitive, astronauts would have aged significantly less, lacking in fuel and technology, speeds reached by astronauts (max 0.01c) provide negligible relativistic effects
theory + evidence supporting relativity	Einstein's predictions could not be tested at the time because technology was not available. Atomic clocks were synced, then one flown around the world in a high speed aircraft - the clock had slowed down slightly. Particle accelerators allow subatomic particles to be accelerated to very fast speeds and their masses observed to increase exponentially.

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	Created by Grace Easton over 7 years ago