P6 Space physics

Question 1

What does the Solar System contain of ?

Answer 1

• The Sun
• 8 planets
• Natural and artificial satellites
• Minor planets including dwarf planets e.g Pluto and asteroids in the asteroid belt

Question 2

Describe the characteristics of the Sun in the Solar System ?

Answer 2

• The Sun is the closest star to the Earth
• It is found at the centre of the Solar System

Question 3

What is a planet ?

Answer 3

A large, spherical object that orbits the Sun

Question 4

Describe characteristics of the planets in the Solar System and their orders ?

Answer 4

• A planet’s gravitational field strength is strong enough to pull in nearby objects (except natural satellites)
• There are 8 planets orbit the Sun
• Closest to furthest from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

Question 5

What are the 2 groups of planet ?

Answer 5

1. The inner rocky planets (4 inner planets)
2. The outer gas giants (4 outer planets)

Question 6

What is a dwarf planet and give its characteristics ?

Answer 6

A very small planet (too small to be called a planet) that orbits the Sun
- A dwarf planet’s gravitational field strength is not strong enough to pull in nearby objects like a planet can
e.g Pluto

Question 7

What is an asteroid and give its characteristics ?

Answer 7

An object much smaller than a dwarf planet, that orbits the Sun
- Most asteroids are found in the asteroid belt
=> multiple asteroids orbiting between Mars (last inner rocky planet) and Jupiter (first outer gas giant)

Question 8

What are the 2 types of satellites in the Solar system and give examples for each ?

Answer 8

1. Natural satellite: an object that orbits a planet e.g the Moon
2. Artificial satellite: a man-made object that orbit another object in space
   e.g GPS satellites, weather satellites, International Space Station

Question 9

What does orbiting body mean ?

Answer 9

A body (object) that orbits around another body
e.g a planet is an orbiting body around the Sun

Question 10

How are astronomical distances can be measured ?

Answer 10

Astronomical distances can be measured in light-years where one light-year is the distance travelled in (the vacuum of) space by light in one year

Question 11

The formula to calculate the time it takes for light to travel a significant distance such as between objects in the Solar System ?

Answer 11

Time = total distance/speed of light
Time: second (s); Distance: metre (m); Speed of light: 3x10^8 m/s

Question 12

What is the distance of one light-year ?

Answer 12

9.46 x 10^15 m

Question 13

Explains why the planets orbit the Sun ?

Answer 13

• The Sun contains most of the mass of the Solar System (more than 99%)
• Bigger mass = bigger gravitational attraction force towards its centre
  => large bodies (planets, dwarf planet) are attracted to the Sun due to the Sun’s massive gravitational force acting on them

Question 14

What is orbital speed and its formula ?

Answer 14

The speed of an object as it orbits around a large body (e.g the Sun)
v = 2π r/ T
v: orbital speed of object (m/s)
r: orbital radius (m)
T: orbital period (s)

Question 15

What is the orbital radius and orbital period ?

Answer 15

• Average distance of the planet from a large body (e.g the Sun)
• Time taken for an object to fully travel 1 circumference of the circle around a large body (e.g the Sun)

Question 16

What is the force that keeps an object orbit around the Sun ?

Answer 16

The force that keeps an object in orbit around the Sun is due to the gravitational attraction of the Sun

Question 17

What happens to the Sun’s gravitational field and the orbital speeds of planets as distance from the Sun increases ?

Answer 17

As distance from the Sun increases:
- The strength of the Sun’s gravitational field decreases
- The orbital speeds of the planets decrease

Question 18

What is the Sun ?

Answer 18

A star of medium size, consisting mostly of hydrogen and and helium, it radiates most of its energy in the infrared, visible and ultraviolet regions of the electromagnetic spectrum

Question 19

What are stars ?

Answer 19

Stars are powered by nuclear reactions that release energy and that in stable stars the nuclear reactions involve the fusion of hydrogen into helium

Question 20

How are stable stars formed (standard definition) ?

Answer 20

Stable stars are formed as protostars from interstellar clouds of gas and dust due to gravitational attraction

Question 21

How are stable stars formed in details ?

Answer 21

• Interstellar cloud of gas and dust compress due to gravitational attraction of particles towards each other into protostar (hot ball of gas)
• When inward gravitational attraction force is balanced by outward force due to high temperature inside the star forms a stable star

Question 22

What can the nebula from a supernova form ?

Answer 22

The nebula from a supernova may form new stars with orbiting planets

Question 23

Describe the life cycle of a small mass star (about the same mass as the Sun) ?

Answer 23

1. Stable star of small mass doing nuclear fusion of hydrogen into helium; when all hydrogen runs out =>
2. Red giant, outer layers of the star expand & cool => it becomes bigger; when nuclear fusion stops =>
3. Planetary nebula: formed when outermost layers of the star are pushed away; when the core of the star collapses =>
4. White dwarf: dead star that still glows, found at the centre of a planetary nebula

Question 24

Describe the life cycle of a large mass star ?

Answer 24

1. Stable star of large mass doing nuclear fusion of hydrogen into helium; when all the hydrogen runs out =>
2. Red supergiant, outer layers of the star expand & cool => it becomes bigger; when nuclear fusion stops =>
3. Supernova: an exploding red supergiant (a “supernova” is an explosion); when the core of the red supergiant star collapses =>
4. Neutron star: made of neutrons, very dense (not as much as black hole)

Question 25

Describe the life cycle of a very large mass star ?

Answer 25

1. Stable star of very large mass doing nuclear fusion of hydrogen into helium; when all hydrogen runs out => 2. Red supergiant, outer layers of the star expand & cool => it becomes bigger; when nuclear fusion stops => 3. Supernova: an exploding red supergiant (a "supernova" is an explosion); when the core of the red supergiant star collapses => 4. Black hole (extremely dense)

Question 26

What is an interstellar cloud ?

Answer 26

A cloud of gas and dust that occupies the space between stars

Question 27

What is a planetary nebula ?

Answer 27

Bubble of gas surrounding a white dwarf that used to be the outer shell of a red giant that it collapsed from

Question 28

What is a protostar ?

Answer 28

A very young star that is still gathering mass from its parent molecular cloud

Question 29

What are galaxies ?

Answer 29

Galaxies are each made up of many billions of stars

Question 30

Briefly describe out place in the universe ?

Answer 30

- The Sun is the closest star to the Earth - The Sun is a star in the galaxy known as the Milky Way - Other stars that make up the Milky way are much further away from the Earth than the Sun is from the Earth

Question 31

What information can be given about the Milky Way ?

Answer 31

- The Milky Way is one of many billions of galaxies making up the Universe - The diameter of the Milky Way is approximately 100 000 light-years

Question 32

What does the Big Bang theory state ?

Answer 32

- The Universe expanded from a single point of high density and temperature (therefore high mass) & rapidly expanded from that point - The Universe is still expanding - The Universe is approximately 13.8 billion years old

Question 33

What is centripetal force and explains the orbital motion of planets around the Sun ?

Answer 33

- A resultant force, acting towards the centre of the circle - For an object orbiting large body e.g Sun, centripetal force = gravitational attraction force - Due to Fnet = ma, the object accelerates towards the centre of the circle - But object also moving forward => acceleration only changes direction of motion but speed of object stays the same (constant speed, changing velocity)

Question 34

What is the formula to calculate how much the gravitational force decreases by with distance from the Sun ?

Answer 34

Gravitational attraction force decreases by 1/x^2, where x = distance from Sun