Space Physics Flashcards
Give two reasons why scientists use models
to demonstrate phenomena that are too big/ too small to see
(or difficult to see)
to make predictions or explanations of observations
A student is modelling red shift. She draws a wave on a piece of elastic. Suggest how she can use the elastic to show how light is red-shifted. Explain what the model shows
pull the elastic to make it longer
it shows that as space expands, the wavelength of the radiation increases
give two similarities between an artificial and a natural satellite
they are both in orbit around a planet
due to the force of gravity
describe what the big bang theory states about the how the universe began
(the universe began as) a massive explosion
from a very small, hot, dense region of space
suggest how elements that were formed in a supernovae ended up on Earth
supernovae exploded
scattering elements throughout our universe
(gravity pulls them together to make stars and planets)
suggest why it is more difficult to fuse elements as they get more massive
fusion involves the joining of nuclei
which are positively charged so repel
larger nuclei mean more charge, and a bigger repulsive force
what do all stars start off as
huge clouds of dust and gas called a nebula
what force is responsible for forming a protostar from a nebula
gravity
How does a main sequence star remain stable
(fusion reactions produce outward forces )
radiation pressures outwards balance the inward gravitational forces
What determines the lifecycle of a star
mass
how are naturally occuring elements formed
Heavy elements can be formed from light ones by nuclear fusion reactions; these are nuclear reactions in which atomic nuclei merge together.
from NUCLEAR FUSION
which elements are only produced in a supernovae
elements heavier than iron
how are elements distributed throughout the universe
massive stars exploding in a supernovae
how does the force of gravity make the objects in orbit change their velocity but not their speed
gravity provides a centripetal force, which keeps orbiting objects moving in a circle - they are constantly changing direction
to change the speed of an object in stable orbit what factor must change
radius of the orbit
what is red-shift?
WAVELENGTHS of light get LONGER if the light source is moving away from the observer
what evidence suggests that the universe is expanding
RED SHIFT
light from more distant galaxies is MORE red-shifted, so these more distant galaxies are moving FURTHER AWAY
what is the name of the scientific theory for the origin of the universe that suggests it started off as an extremely small, hot and dense region?
the Big Bang theory
0 1 . 1 Describe the way in which the absorption lines which we observe in the
light we receive from a distant galaxy differ from those of the Sun.
0 1 . 2 Explain the reason for this difference.
01.1 The absorption lines in the light we receive from a distant galaxy are redshifted / longer in wavelength [1].
01.2 The distant galaxy is moving away from us [1]. This causes the light we
receive from it to be red-shifted.
0 1 . 4 Edwin Hubble was the first person to investigate how the red-shift of a
galaxy depended on its distance from us.
Describe the trend which is shown in the above graph.
- 5 Explain the significance of this trend in relation to the development of the
Universe.
As the distance to a galaxy increases, the amount of red-shift in the light
we receive from it increases / red-shift is proportional to distance [1].
01.5 This tells us that galaxies which are further from us are moving away
from us more quickly [1], which means that the Universe is expanding
and that there must have been a point at which this expansion began
(which we call the Big Bang) [1].
A teacher uses a starry balloon to explain the expansion of the Universe. She tells the class that the motion of the stars printed on the surface of the balloon as it is inflated as like the motion of the stars in the Universe as it expands. Write down one strength and one weakness of this model for the expansion of the Universe.
Strength As time increases, the stars on the surface of the balloon move away from one another (just as stars in the Universe are moving away from one another).
Weakness Any ONE of:
- balloon move away from one another will decrease with time (we believe that the rate at which our Universe is expanding may be increasing with time due to dark energy).
- the balloon can only expand so much (but the Universe may be infinite);
0 1 A communications satellite is in orbit around the Earth, as shown below.
0 1 . 2 Write down the origin of this centripetal force.
01.2 Gravity (the gravitational force exerted on the satellite by the Earth) [1].
0 1 . 4 Although the speed of the satellite in its current orbit (orbit 1) is constant,
its velocity is constantly changing. Explain why.
Velocity is a vector: the direction of the satellite is constantly changing as
it follows its circular orbit around the Earth [1].
When the speed of the satellite decreases, the gravitational / centripetal
force acting on it will cause its height above the surface / orbital radius
to change as shown [1].
When it has reached orbit 2, the gravitational / centripetal force acting on
it will be just strong enough to keep it moving in a circle at this height
above the surface / at this orbital radius [1].
Centri-what-now?! This is a fairly tricky concept. Think of it this way: if we tried to
(somehow) pull the satellite closer to Earth when it was in orbit 2, then let go of it again,
it would naturally drift back into orbit 2 because it would be travelling too quickly for a
lower orbit. It would stop drifting away from the Earth (and therefore settle into orbit 2)
at the point at which the centripetal force acting on it (due to gravity) was just strong
enough to maintain its circular motion about the Earth.
Think about what happens when a car drives round a bend in the road too quickly: if the
friction between the tyres and the road isn’t strong enough, then the car will drift
towards the outside of the bend (to a larger radial distance from the centre of curvature
of the bend) until the frictional force (acting towards the centre of curvature) is just
strong enough to maintain the circular motion of the car.
You could also approach this question the other way round: if the speed of the satellite
was increased then it would be moving too quickly to remain in orbit 1 – in other words,
the centripetal (gravitational) force acting on it in orbit 1 would no longer be strong
enough to maintain its circular motion. It would then drift outwards, settling into orbit 3.
In this orbit, the gravitational force exerted on the satellite by the Earth is lower (because
it is further from the Earth), but it is just strong enough to keep an object moving in the
circular path of this orbit.
Don’t feel too bad if this all seems very confusing at first – this is a topic which many Alevel Physics students find confusingly – but do at least try to ensure that you
understand the above answer for your exam.
