8. Space Physics

Question 1

How many stars are in our solar system?

Answer 1

One - the sun

Question 2

What are natural satellites?

Answer 2

The moons that orbit planets

Question 3

What is our solar system a small part of?

Answer 3

The Milky Way galaxy

Question 4

Why is Pluto no longer classified as a planet?

Answer 4

• other objects started to orbit near Pluto with masses similar to pluto (Kuipur belt)
• as well as orbiting, a planet has to ‘clear the neighbourhood around it’s orbit’ which pluto has not done

Question 5

What keeps the planets in their circular orbit around the sun?

Answer 5

• gravity

* don’t fall as they’re moving very quickly - centripetal force

Question 6

What is a centripetal force?

Answer 6

When an object moves in a circular path and there is a resultant force acting towards the centre of the circle

Question 7

When does the size of the centripetal force increase?

Answer 7

• when the MASS or SPEED of the object increases (more MOMENTUM = bigger force to change it)
• the radius decreases - a tighter turn needs a bigger force

Question 8

What are some examples of forces that can provide the centripetal force?

Answer 8

• friction (e.g. a car on a roundabout)

* gravity (e.g. a planet)

Question 9

What does it mean for an object’s velocity and direction if it is travelling in a circle?

Answer 9

• it’s constantly changing direction so it is constantly accelerating
• this means it’s constantly changing velocity (but not changing speed)

Question 10

How was the solar system formed?

Answer 10

• 6 billion years ago - old star exploded (supernova) and clouds of gas and dust called nebula formed
• the nebula was pulled together due to gravity and formed planets
• if the planets were big, dense and hot enough then a star would have formed and fusion would’ve occurred

Question 11

Are all stars the same?

Answer 11

They form in the same way but there is a huge range of masses

Question 12

How are stars formed?

Answer 12

Gravity pulls together a gas nebula which heats up until fusion starts

Question 13

What is the life cycle of a star that ends up as a black dwarf?

Answer 13

• nebula
• protostar
• main sequence star
• red giant
• white dwarf
• black dwarf

Question 14

What is the life cycle of a star that ends up as a neutron star?

Answer 14

• nebula
• protostar
• main sequence star
• red super giant
• supernova
• neutron star

Question 15

What is the life cycle of a star that ends up as a black hole?

Answer 15

• nebula
• protostar
• main sequence star
• red super giant
• black hole

Question 16

What size are red giants?

Answer 16

About the same size as the sun

Question 17

What size are super red giants?

Answer 17

Much bigger than the sun

Question 18

What is it called when a star first begins to shine?

Answer 18

A protostar

Question 19

What happens when a protostar has contracted enough so that it is very hot and dense?

Answer 19

Nuclear fusion starts and releases energy to form a main sequence star

Question 20

What type of star is the sun?

Answer 20

A main sequence star

Question 21

Why is the main sequence the longest stage in a star’s life?

Answer 21

The gravity inwards is balanced by radiation pressure pushing outwards

Question 22

Why does a star collapse after hydrogen runs out and fusion stops?

Answer 22

Gravity is greater than radiation pressure so the star collapses

Question 23

How is a red giant formed?

Answer 23

After a star collapses, the star heats up enough for helium to fuse and it expands (radiation pressure > gravity)

Question 24

Does fusion occur in red giants?

Answer 24

Yes - it forms lighter elements up to iron

Question 25

What happens for small stars like the sun after fusion stops?

Answer 25

There is a hot core left behind - a white dwarf

Question 26

How is a black dwarf formed?

Answer 26

A white dwarf cools

Question 27

What happens for massive stars when fusion stops?

Answer 27

Gravity collapses the star dramatically and it rebounds as a supernova

Question 28

What happens after a supernova?

Answer 28

A dense core called a neutron star is left over, or a black hole if it's so dense that light cannot escape from it

Question 29

How is helium formed in stars?

Answer 29

When a protostar becomes hot and dense enough for fusion - hydrogen fuses to make helium in a main sequence star

Question 30

How are light elements including iron formed in stars?

Answer 30

During the red giant stage of a star these elements are formed by nuclear fusion

Question 31

What is the heaviest element formed in a star?

Answer 31

Iron

Question 32

How are heavy elements formed in stars?

Answer 32

Because the energy of a supernova is so big it can force nuclei to fuse

Question 33

What are some of the elements formed in supernovae?

Answer 33

gold, uranium

Question 34

How do we know that our solar system formed from the remnants of a supernova?

Answer 34

The presence of heavy elements like gold - they can only be formed in a supernova

Question 35

Why is a main sequence star so stable?

Answer 35

Gravity = radiation pressure, and there is enough hydrogen fuel so density and temperature stay constant

Question 36

What is the Doppler effect?

Answer 36

The change in frequency of a wave, caused by relative motion between the source of the wave and the observer

Question 37

Why is the pitch higher when a car is moving towards you?

Answer 37

Wavelength is decreased so frequency is increased

Question 38

Why is the pitch higher when a car is moving away from you?

Answer 38

Wavelength increases so frequency has decreased

Question 39

What is red-shift?

Answer 39

Hubble's idea - the increase in wavelength of the light emitted by a distant galaxy moving away from us

Question 40

What are 4 of Hubble's ideas?

Answer 40

1. distant galaxies are red-shifted 2. the further away the galaxy, the larger the red shift 3. distant galaxies must be moving away from us 4. very distant galaxies must be moving faster than the closer ones

Question 41

What happens to red shift when a galaxy is further away?

Answer 41

There is a greater red shift

Question 42

Which has a longer wavelength, red or blue light?

Answer 42

Red

Question 43

What is a galaxy?

Answer 43

A collection of billions of stars

Question 44

What did Hubble use red-shift as evidence for?

Answer 44

That the universe is expanding

Question 45

What are the two main theories about the creation of the universe?

Answer 45

* big bang theory | * steady state theory

Question 46

What is the big bang theory?

Answer 46

* the universe began with all space, time and matter in a single point which was hot and dense * an explosion caused it to expand * the universe has been expanding ever since

Question 47

What is the steady state theory?

Answer 47

* the universe has always existed | * galaxies are being pushed apart due to matter entering the universe through 'white holes'

Question 48

What is the microwave radiation coming from every direction of space?

Answer 48

Cosmic background radiation - created as gamma radiation after the big bang

Question 49

Why is cosmic background radiation no longer gamma?

Answer 49

As the universe has expanded the wavelength has stretched to longer wavelengths

Question 50

How is cosmic background radiation evidence for the big bang theory?

Answer 50

It could have only been created during the big bang