topic eight: space physics

Question 1

how does the sun release energy?

Answer 1

by nuclear fission

Question 2

define: a planet

Answer 2

a large body which orbits the sun

Question 3

what are the first four planets of our solar system?

Answer 3

mercury, venus, earth and mars

Question 4

what makes the first four planets different from the rest

Answer 4

they all have hard rocky surfaces

Question 5

what are the outer planets of our solar system?

Answer 5

jupiter, saturn, uranus, neptune

Question 6

how are these planets different from the first four?

Answer 6

they are all made up of gas and are much larger

Question 7

define: a moon

Answer 7

a natural satellite in orbit around a planet

Question 8

define: a dwarf planet

Answer 8

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

Question 9

what are the three things gravity causes?

Answer 9

• 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

Question 10

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

Answer 10

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.

Question 11

what is a galaxy?

Answer 11

a large group of stars

Question 12

when was the sun formed?

Answer 12

4.6 billion years ago

Question 13

define: a protostar

Answer 13

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

Question 14

what happens in a protostar?

Answer 14

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

Question 15

define: a main sequence star

Answer 15

a star that releases energy by fusing hydrogen to form helium

Question 16

what happens inside of a main sequence star?

Answer 16

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

Question 17

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

Answer 17

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

Question 18

what happens after a star runs out of hydrogen?

Answer 18

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

Question 19

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

Answer 19

the star swells up into a red giant

Question 20

define: a red giant

Answer 20

a very large star which fuses helium into heavier elements

Question 21

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

Answer 21

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

Question 22

what happens after a star turns into a white dwarf?

Answer 22

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

Question 23

what happens to larger main sequence stars?

Answer 23

it also begins to collapse but becomes a red super giant

Question 24

what happens inside of a red super giant

Answer 24

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

Question 25

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

Answer 25

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

Question 26

define: a supernova

Answer 26

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

Question 27

define: a neutron star

Answer 27

a very dense small star made out of neutrons

Question 28

define: a black hole

Answer 28

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

Question 29

what causes the earth to accelerate?

Answer 29

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

Question 30

what are the conditions in a circular orbit?

Answer 30

- 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

Question 31

whats the formula for calculation the speed of an orbit?

Answer 31

2 x π x orbital radius ------------------------------ time taken for orbit

Question 32

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

Answer 32

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

Question 32

three important facts about light emitted by distant galaxies:

Answer 32

- 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

Question 33

what is the big bang theory?

Answer 33

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

Question 34

how does red-shift support the big bang theory?

Answer 34

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

Question 35

how did aristotle arrange the universe?

Answer 35

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

Question 36

what was copernicus' theory

Answer 36

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)

Question 37

what discoveries did galileo make?

Answer 37

- the moon varies in brightness - venus has phases like the moon - jupiter had four moons

Question 38

explain galileo's points

Answer 38

- 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