space physics (p8)

Question 1

describe the planets in the solar system, and the sun:

Answer 1

• at the centre is the sun, which is a star.
• mercury, venus, earth and mars are relatively small rocky planets.
• jupiter, saturn, uranus and neptune are much larger.
• beyond the orbit of neptune, we have a number of dawrf planets, one of which is pluto.
• the dwarf planets are extremely small.
• all orbit the sun in a slightly elliptical orbit (not a perfect circle, it’s slightly squashed)

Question 2

what is the difference between asteroids and comets?

Answer 2

• asteroids are mostly made of rock and metal, and are mainly found in the asteroid belt (between mars and jupiter)
• comets are made mostly of ice and dust. they also orbit the sun in an elliptical orbit, and tend to be towards the edge of the solar system (beyond neptune)

Question 3

what else does the solar system contain?

Answer 3

a number of other objects besides planets. for example, moons, asteroids and comets.
- moons are natural satellites which orbit planets.
- most planets in the solar system have at least one moon, some planets have a large number of moons.

Question 4

describe the milky way galaxy:

Answer 4

• the solar system is just a tiny part of the milky way galaxy.
• a galaxy is a massive group of stars, most of which contain their own star systems
• in the universe, there are hundreds of billions of galaxies.
• all held together by gravity, and all the galaxies spin around the middle in the same way planets orbit the sun

Question 5

describe the universe:

Answer 5

• scattered with galaxies, but mainly empty space (similar to galaxies)

Question 6

what is the difference between a solar system and a star system?

Answer 6

solar system: our sun and the surrounding planets
star system: any other star and its orbiting planets

Question 7

how do stars form?

Answer 7

• stars form from clouds of dust and gas - this is called a nebula.
• in a nebula, the gas is mainly hydrogen.
• in the first stage, gravity causes the cloud of dust and gas to collapse.
• as the dust particles move faster, the temperature rises to millions of degrees celsius (gravity ‘squeezes’ the star, meaning the particles collide more, raising the temperature), it gets more dense
• this collapsing cloud of dust and hot gas is called a protostar.
• as more particles collide and join the protostar, it gets bigger, meaning its force of gravity gets stronger, attracting even more dust and gas
• if the temperature of the protostar gets high enough, the hydrogen nuclei undergo nuclear fusion to form helium NUCLEAR FUSION
• nuclear fusion releases a lot of energy, keeping the core of the star hot
• at this point, the protostar has turned into a main sequence star.

Question 8

describe what happens to a star when it undergoes nuclear fusion:

Answer 8

• there are two opposing forces acting within the star.
• the force of gravity acts inwards, and tends to make the star collapse.
• the energy from nuclear fusion creates a force acting outwards. this tends to make the star expand.
• the force of gravity acting inwards is balanced due to the force of fusion acting outwards.
• because these two forces are balanced, scientists would say that the star is in equilibrium, and this can result in a long stable period that lasts for billions of years
• our sun is currently in this stage

Question 9

what happens to main sequence stars?

Answer 9

• the hydrogen nuclei had been fusing together to form helium nuclei.
• at some stage the hydrogen in the star will begin to run out, which is basically its fuel
• therefore the outward force due to fusion is less than the inward force due to gravity, causing the star to collapse inwards.
• the collapse of the star causes its temperature to increase, as it’s now a small, hot, dense ball
• now helium nuclei fuse together to create heavier elements, including all elements up to iron on the periodic table (NUCLEAR FUSION starts up again), and the star expands to form either a red giant or a red super giant

Question 10

what happens to main sequence stars the same size as our sun?

Answer 10

• the red giant, after a short time, will become unstable and expel its outer layers of dust and gas
• this leaves behind a hot, dense, solid core which doesn’t do any nuclear fusion: white dwarf
• over time, this white dwarf gets cooler and darker as it emits all of its energy, and will transition to a black dwarf (no longer any energy to emit light, will appear dark)

Question 11

what happens to main sequence stars that are much bigger than our Sun?

Answer 11

• once again, helium nuclei fuse together to produce heavier elements.
• once again, the red super giant stops carrying out nuclear fusion. keeps up this cycle of expanding and contracting for a while
• at the end, the star explodes - this is called a supernova.
• the temperature in a supernova explosion is incredibly high, creating elements heavier than iron.
• these elements are then distributed throughout the universe

Question 12

what could happen to the star after a supernova?

Answer 12

• if the star was simply very big, it will condense into a very dense core, called a neutron star
• if the star was absolutely massive, it could collapse in on itself, and become a black hole

Question 13

why is a black hole called a black hole?

Answer 13

so dense that its gravity is able to pull in any light that passes nearby. appears as a hole in the Universe, emitting no light

Question 14

what are the limitations of nuclear fusion, and how are these limitations overcome?

Answer 14

• nuclear fusion, in any of the red giant stages, and in any of the stages up until red super giant, cannot create any elements heavier than iron.
• the temperature of a supernova explosion is high enough to create elements heavier than iron.

Question 15

describe how the Earth and the moon stay in orbit of the Sun and the Earth, respectively:

Answer 15

• the force of gravity acting between the Sun and the Earth holds the Earth in its orbit.
• the moon also has a circular orbit around the Earth. this is called a natural satellite, and once again, the force of gravity holds the moon in its orbit.

Question 16

how does the force of gravity lead to a change in velocity but not a change in speed in satellites?

Answer 16

as objects are orbiting the Earth in a circular motion, this means their direction is constantly changing. therefore even if its speed is remaining the same, as the direction is constantly changing, the velocity must also be constantly changing (vector quantity).

Question 17

what is a satellite?

Answer 17

any object that orbits a celestial body, such as a star or planet
- can be either natural or artificial

Question 18

define orbit:

Answer 18

the curved path of one celestial object/space craft around another celestial object

Question 19

give an example of a natural satellite:

Answer 19

moon

Question 20

describe geostationary satellites and general satellites:

Answer 20

• artificial satellites are man-made.
• used for communication and orbiting telescopes
• geostationary satellites orbit once every 24 hours, so they point at the same part of the Earth.
• other artificial satellites orbit more frequently.

Question 21

describe orbits:

Answer 21

• the force of gravity holds objects in their orbit, and satellites are no exception.
• in the case of circular orbits, the force of gravity is leading to a change in velocity, but not a change in speed.
• therefore the satellite is constantly accelerating, as acceleration = change in velocity / time
• if the speed of a satellite changes, the orbit radius must also change.
• if the speed of the satellite increases, the radius of its orbit decreases. this is because at a higher speed, the object requires a higher force of gravity to prevent it from flying off into space. by staying closer to the Earth, the gravitational force on the object is greater, and the object remains in stable orbit.

Question 22

why do objects stay in orbit?

Answer 22

• Newton’s first law: an object travelling at a certain velocity will continue at this velocity unless acted on by a resultant force
• the Earth is so massive and close to the moon, so it exerts a strong gravitational pull which is felt as an attractive force towards the Earth
• however, as the moon is large, and travelling fast, it has a lot of momentum in its forwards direction, so the gravitational force isn’t strong enough to completely pull it into the Earth, it can only change its direction very slightly
• the Earth is always applying this gravitational force, so always changing the moon’s direction. the moon is always orbiting around the Earth

Question 23

describe the discovery of red-shift:

Answer 23

• in the 1900s, astronomers were looking at the light emitted from different galaxies.
• they detected that the light from very distant galaxies has an increased wavelength compared to light from closer galaxies.

Question 24

what is the main point of red-shift?

Answer 24

from Earth, every direction we look into space, the galaxies seem to be moving further and further away from us (the Universe is expanding)
- the main evidence for this is the red shifting of light from the galaxies. the explanation is the Big Bang theory

Question 25

what are absorption spectra, and how do they change?

Answer 25

- there is a spectrum of all visible light emitted from the sun, and observed here on Earth - on the left is the longer, red wavelengths, and on the right are the shorter purple wavelengths - the sun's atmosphere has certain chemicals (e.g. oxygen, hydrogen) that can absorb certain wavelengths of light - this means that when the light reaches Earth, certain wavelengths are missing, and the absorption spectrum ends up with a pattern of dark lines -------------------------------------------------------------- - analysing lines from distant galaxies shows the black lines in exactly the same pattern, but shifted towards the red end of the spectrum (RED SHIFT)

Question 26

describe red shift, keeping in mind absorption spectra:

Answer 26

refers to the absorption spectra from distant galaxies shifting towards the red end. this is because all of the light rays are stretched as they make their way to Earth, and so are shifted towards the red end as red wavelengths are longer - this may be because the distant galaxies are moving away from us, so the waves are stretched when travelling towards us - however, the distant galaxies aren't moving away by travelling through space, but rather because the space between us and the galaxies is expanding

Question 27

complete the sentence: the further away a galaxy is __________________________.

Answer 27

the further away a galaxy is, the more quickly it appears to be moving away.

Question 28

describe the balloon model, and what are its limitations?

Answer 28

- balloon with markers on its surface - blow up the balloon, so the markers space out, but not because they're physically moving, but because the space in between them is stretching LIMITATIONS: - balloons only stretch so far until they burst, whereas the universe won't burst - if this were meant to represent the Universe, the galaxies should be inside the balloon rather than on its surface

Question 29

how can we use the idea of red-shift to provide evidence of the Big Bang Theory?

Answer 29

- the fact that distant galaxies are moving faster than nearby galaxies provides evidence that the Universe is expanding. - scientists believe that the Universe began from a very small region that was extremely hot and dense. - this region then exploded and expanded into the Universe we see today. this is the Big Bang Theory. - around 1998, astronomers noticed something very strange. they'd assumed that gravity would cause the expansion of the Universe to gradually slow down, but observations of supernovae showed that the rate of expansion is actually increasing.

Question 30

how do fusion processes lead to the formation of new elements?

Answer 30

nuclear fusion is a nuclear reaction in which two or more atomic nuclei collide at nearly the speed of light to join to form a new type of nucleus. - this creates new elements. - hydrogen and helium nuclei can then be fused into heavier elements.

Question 31

what is the difference between centrifugal force and gravitational force?

Answer 31

- centrifugal force is the apparent outward force experienced by an object moving in a curved path. it arises due to an object's inertia, which resists it being pulled to the centre of the orbit. - gravitational force pulls the object towards the centre of the massive body it is orbiting. - when an object is in orbit, the centrifugal forces and gravitational forces acting on it must be equal, to prevent it from flying into space or crashing into the body.

Question 32

how does the radius of the object's orbit adjust to accommodate new speeds?

Answer 32

- when the speed of an object in a stable orbit changes, the balance between the centrifugal force and the gravitational force is disrupted - if the object's speed increases, the centrifugal force will become stronger. To counteract this increased outward force, the gravitational force needs to become stronger as well. This can only be achieved by moving the object closer to the centre of the orbit, reducing the radius - if the object's speed decreases, the centrifugal force will weaken. To restore the balance, the gravitational force must also weaken. This is accomplished by moving the object farther away from the centre of the orbit, increasing the radius

Question 33

why do scientists believe in the Big Bang theory?

Answer 33

its predictions are supported by observations