space physics

Question 1

What does our solar system contain?

Answer 1

• One star (the Sun)
• Eight planets
• Dwarf planets
• Natural satellites (the moons)

Question 2

Describe the Sun in terms of its position in the solar system

Answer 2

• The sun lies at the centre of our solar system, it is heliocentric.

Question 3

What orbits the Sun?

Answer 3

• The eight planets and the dwarf planets orbit around the Sun

Question 4

What orbits the planets?

Answer 4

• Natural satellites (the moons) orbit planets

Question 5

Define a planet

Answer 5

• Large objects that orbit a star
• Large enough so that their gravity is strong enough to have pulled in any nearby objects apart from their satellites

Question 6

List the planes that orbit the Sun in order

Answer 6

• Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, (pluto)

Question 7

Define a dwarf planet

Answer 7

• Planet-like objects that orbit stars, but don’t meet the rules of being a planet

Question 8

Give an example of a natural satellite

Answer 8

• Not man-made
  e.g. the moon

Question 9

Define an artificial satellite

Answer 9

• Satellites that humans have built
• They generally orbit the Earth

Answer 10

• There are also asteroids and comets

Question 11

What is our solar system a small part of?

Answer 11

• Our solar system is a small part of the Milky Way galaxy

Question 12

Define the Milky Way galaxy

Answer 12

• A collection of billions of stars that are all held together by gravity

Question 13

How was the sun formed?

Answer 13

• The Sun was formed from a cloud of dust and gas (nebula) pulled together by gravitational attraction

Question 14

Describe the differences between the planets

Answer 14

• Smaller planets are made of primarily rock whereas larger planets are primarily gas
• Planets rotate at different speeds
• Some planets rotate in the opposite direction or on a skewed axis to the other planets - may be due to past collisions throwing its axis off balance
• Larger planets have rings - gravitational field is so strong it attracts debris

Question 15

Describe the similarities between the planets

Answer 15

• All planets orbit the Sun on the same plane
• All planets rotate

Question 16

What were the initial theories about the solar system?

Answer 16

• Initially, Earth was at the centre, the planets, our moon, and the sun, orbited the Earth
• “Geocentric” model
• Everything orbited in perfect circles
• With a fixed background of stars

Question 17

When was the heliocentric model formed?

Answer 17

• 600 years after the geocentric model

Question 18

What was the evidence for the heliocentric model?

Answer 18

• The main evidence being Mars’ “retrograde motion” - Earth orbits the Sun faster than Mars, so we undertake it (appears to reverse its direction in the sky)
• Galileo observing moons orbiting Jupiter showed not everything orbited the Earth
• Kepler showed that the planets orbited in ellipses, and not circle

Question 19

• (HT only) for circular orbits, the force of gravity can lead to changing velocity but unchanged speed

Answer 19

*As the planet orbits the sun, the gravitational force causes the planet to change direction constantly (it moves in a circle around the sun)
* This means the velocity is always changing
* Hence the force causes the planet to accelerate without increasing its
speed

Question 20

(HT only) for a stable orbit, the radius must change if the speed changes.

Answer 20

For a stable orbit: the radius must change if the speed changes
* If the planet moves closer to the sun, (i.e. its orbital radius decreases)
* The gravitational attraction to the sun increases (Force increases, and so does acceleration)
* So the orbital speed of the planet increases

Question 21

Explain how, at the start of a star’s life cycle, the dust and gas drawn together by gravity causes fusion reactions

Answer 21

• Dust & gas cloud is present in a galaxy - the gravitational attraction between the gas/dust particles draws them together
• The cloud becomes more concentrated, as the particles get closer
• The temperature and pressure of the cloud increases as the particles get pushed so close together
• Eventually the pressure gets so great that the gas/dust particles are able to fuse together

Question 22

Explain how fusion reactions lead to an equilibrium between the gravitational collapse of a star and the expansion of a star due to fusion energy

Answer 22

• Fusion occurs as the light (mainly hydrogen gas) nuclei fuse together to form helium nuclei
• This creates a large amount of energy
• This release opposes the collapsing of the cloud due to gravity
• So eventually an equilibrium forms, where the energy released due to fusion balances the pressure of gravitational collapse

Answer 23

 This means a star has now formed, and it will stay like this for billions of
years

Answer 24

• Eventually the star runs out of gas to fuse
  o This means it is not in equilibrium, so it collapses

Question 25

Describe the life cycle of a massive star

Answer 25

• The star will collapse, increasing the pressure + temperature of the core,
  meaning heavier elements can fuse. Once all the fusion has happened, it is
  too massive to be stable, so the star collapses, rebounds on its centre and
  produces a supernova
• What remains is either a neutron star or black hole

Question 26

Describe the life cycle of a normal-sized star (the Sun)

Answer 26

• The same process happens (as a massive star), less fusion occurs however (less fuel to fuse)
• The star collapses, and produces a planetary nebula
• A lower scale supernova
• A white dwarf remains

Answer 27

A star goes through a life cycle. The life cycle is determined by the size of the star.

Question 28

What does fusion processes in stars produce?

Answer 28

• Fusion processes in stars produce all of the naturally occurring elements.

Question 29

How are elements heavier than iron produced in a star?

Answer 29

• Elements heavier than iron are produced in a supernova

Question 30

What happens when a massive star explodes (supernova)

Answer 30

• The explosion of a massive star (supernova) distributes the elements throughout the universe.

Question 31

Explain how fusion processes lead to the formation of new elements

Question 32

What does allows planets and satellites to maintain their circular orbits?

Answer 32

• Gravity provides the force that allows planets and satellites (both natural and artificial) to maintain their circular orbits.

Question 33

Describe the similarities and distinctions between the planets, their moons, and artificial satellites

Answer 34

There is an observed increase in the wavelength of light from most distant galaxies. The further away the galaxies, the faster they are moving and the bigger the observed increase in wavelength. This effect is called red-shift.

Question 35

What provides evidence for the expansion of the universe and supports the Big Bang theory?

Answer 35

• The observed red-shift provides evidence that space itself (the universe) is expanding and supports the Big Bang theory.

Question 36

What does the Big Bang theory suggest?

Answer 36

• The Big Bang theory suggests that the universe began from a very small region that was extremely hot and dense

Answer 37

Since 1998 onwards, observations of supernovae suggest that distant galaxies are receding ever faster.

Answer 38

Students should be able to explain:
• qualitatively the red-shift of light from galaxies that are receding

Answer 39

explain that the change of each galaxy’s speed with distance is evidence of an expanding universe

Question 40

Explain how scientists are able to use observations to arrive at theories such as the Big Bang theory

Answer 41

explain • that there is still much about the universe that is not understood, for example dark mass and dark energy.

Question 42

Expalain the red shift

Answer 42

Light appears red shifted from galaxies which are moving away from Earth
- The change with distance of each galaxy’s speed is evidence of an expanding universe
- Imagine start of the big bang as an un-stretched balloon, with galaxies on the surface of the
balloon, and as the universe expands, the balloon expands
o The distance from the galaxies also expands
o So light from a galaxy has its wavelength “red-shifted” as it appears to move away
from us
o As wavelength appears to get larger (more in the red-end of the visible spectrum)
o Frequency appears to decrease, as each time a wavelength is emitted, the source
(galaxy) is further away

Question 43

How does the Red Shift give evidence for the Big Bang?

Answer 43

• This shows universe is expanding
• So initially, it must have been formed from a single point

Question 44

How does Cosmic Microwave Background radiation give evidence for the Big Bang?

Answer 44

• CMB
  o Cosmic Microwave Background radiation
  o When the universe was very young, everything, the first stars and rock, would be
  very hot, and should have emitted lots of short-wavelength radiation
  o This radiation, as the universe expanded over time, would have been stretched to
  become microwaves
  o This background radiation is present wherever you point a telescope in the sky
  o Which proves that the hot young universe has cooled and expanded since
• As the big bang accounts for all the experimental evidence, it is the most accepted model currently
  There is much about the universe that is not understood, for example dark mass and dark energy