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aqa gcse physics > topic eight: space physics > Flashcards

topic eight: space physics Flashcards

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1
Q

how does the sun release energy?

A

by nuclear fission

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2
Q

define: a planet

A

a large body which orbits the sun

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3
Q

what are the first four planets of our solar system?

A

mercury, venus, earth and mars

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4
Q

what makes the first four planets different from the rest

A

they all have hard rocky surfaces

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5
Q

what are the outer planets of our solar system?

A

jupiter, saturn, uranus, neptune

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6
Q

how are these planets different from the first four?

A

they are all made up of gas and are much larger

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7
Q

define: a moon

A

a natural satellite in orbit around a planet

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8
Q

define: a dwarf planet

A

a planet large enough for its own gravity to have shaped it roughly spherical but not large enough to qualify as one of the main planets

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9
Q

what are the three things gravity causes?

A
  • causes planets to orbit the sun
  • causes the moon and artificial satellites to orbit the earth
  • causes stars to orbit around the center of their galaxies
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10
Q

how does gravity keep the moon in orbit of the earth?

A

in a position on its orbit, m1, the moon has speed v. the pull of gravity deflects its motion. later it has moved to a new position, m2, but it still has speed v. the force of gravity does not make the moon travel any faster but the force changes the direction of motion. this causes the moon to stay in orbit.

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11
Q

what is a galaxy?

A

a large group of stars

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12
Q

when was the sun formed?

A

4.6 billion years ago

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13
Q

define: a protostar

A

the name given to the large ball of gas as it contracts to form a star

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14
Q

what happens in a protostar?

A

the cloud of cold hydrogen gas and dust collapses due to the pull of gravity. as it collapses, molecules collide with each other and their kinetic energy is transferred as thermal energy causing the temperature to rise. the temperature is so high that hydrogen nuclei begin to collide and nuclear fusion begins. a star is born

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15
Q

define: a main sequence star

A

a star that releases energy by fusing hydrogen to form helium

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16
Q

what happens inside of a main sequence star?

A

the forces of gravity fight to collapse the star but the enormous pressure of the fusion energy trying to expand the star balances these inward forces

17
Q

what happens towards the end of a star’s life as a main sequence star?

A

its supply of hydrogen begins to run out making the star become unstable

18
Q

what happens after a star runs out of hydrogen?

A

the pressure inside of the star drops and the star begins to collapse, temperatures spike to 100 million degrees celsius and helium begins to fuse into heavier elements such as carbon and oxygen

19
Q

what happens to a star after elements like carbon and oxygen begin to form?

A

the star swells up into a red giant

20
Q

define: a red giant

A

a very large star which fuses helium into heavier elements

21
Q

what happens when a red giant is no longer able to fuse helium?

A

the star collapses into a white dwarf, fusion stops and the star’s like is over

22
Q

what happens after a star turns into a white dwarf?

A

it cools down and become a dark cold star known as a black dwarf

23
Q

what happens to larger main sequence stars?

A

it also begins to collapse but becomes a red super giant

24
Q

what happens inside of a red super giant

A

in red super giants the fusion energy is sufficient for heavier elements to be made in the fusion process meaning elements up to iron can be fused

25
Q

what happens after a red super giant runs out of nuclear fuel?

A
  1. the star will explode much like a nuclear bomb, this is known as a supernova. the remnants of a supernova are spread out into space and eventually they will collapse to make new stars
  2. at the same time gravitational forces cause the center to collapse into a highly condensed form of matter. the core either becomes a neutron star, which is only made up of neutrons, or the collapse is so complete the star disappears into a microscopic point and becomes a black hole
26
Q

define: a supernova

A

a gigantic explosion caused by runaway fusion reactions in a very large star

27
Q

define: a neutron star

A

a very dense small star made out of neutrons

28
Q

define: a black hole

A

the most concentrated state of matter from which even light cannot escape

29
Q

what causes the earth to accelerate?

A

the pull of gravity, this acceleration causes the earth to change direction

30
Q

what are the conditions in a circular orbit?

A
  • a planet’s velocity changes but its speed remains constant
  • the planet accelerates towards the Sun which causes it to change direction
  • gravity provides the force to accelerate the planet
31
Q

whats the formula for calculation the speed of an orbit?

A

time taken for orbit

32
Q

what is red shift and how is light red-shifted?

A

when a source of light is moving away from us, the wavelength of light that we see become longer so the light moves to the red end of the spectrum. we say that the light has been red-shifted

32
Q

three important facts about light emitted by distant galaxies:

A
  • light emitted from these galaxies is red-shifted this tells us distant galaxies are moving away from us
  • galaxies appear to be moving away from us in all directions
  • the further away from us a galaxy is, the bigger the red-shift meaning the further away a galaxy is, the faster it is moving
33
Q

what is the big bang theory?

A

a theory that suggests the universe began about 13.8 billion years ago when all matter and space expanded violently from a single point

34
Q

how does red-shift support the big bang theory?

A

it shows that galaxies further away move away from us fasts which suggests that at one instant a long time in the past, all galaxies were in the same position

35
Q

how did aristotle arrange the universe?

A

earth at the center and all heavenly bodies moving around it. he thought that the planets and moon moved at different speeds to the stars and thus remained in the same place

36
Q

what was copernicus’ theory

A

he realized the motion of the planets could be explained if the sun stand still at the center of the universe, he used the retrograde motion of mars to explain his theory (earth overtakes mars making it seem to move backwards)

37
Q

what discoveries did galileo make?

A
  • the moon varies in brightness
  • venus has phases like the moon
  • jupiter had four moons
38
Q

explain galileo’s points

A
  • the distance between earth and mars changes so the brightness of mars changes
  • venus lies between us and the sun so sometimes we can see all of its surface illuminated by the sun
  • jupiter appeared to have four moons but sometimes only three were visible proving that the earth was moving too

aqa gcse physics (9 decks)

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