Topic 7

Question 1

7.1P
Describe the relationship between gravity and the weight of an object

Answer 1

Directly proportional

Question 2

7.1P
Describe the relationship between the mass of a planet and the gravity acting on it

Answer 2

Directly proportional
(the greater the m the more g will act)
(moon has less m so less gravity)

Question 3

7.1P
Describe the relationship between radius and surface gravity

Answer 3

Inversely proportional
(Smaller radius -> greater gravity)

Question 4

7.1P
What factors affect the force of gravitational attraction between 2 objects?

Answer 4

-Mass
-d between the masses

Question 5

7.2P
What does the solar system consist of?

Answer 5

-Sun (our star)
-8 planets (and their natural satellites e.g. our moon)
-Dwarf planets
-Asteroids
-Comets

Question 6

7.3P
Recall the names and order of the eight planets from the sun (closest to furthest)

Answer 6

-Mercury
-Venus
-Earth
-Mars
-Jupiter
-Saturn
-Uranus
-Neptune
(My Very Energetic Mother Just Swam Under a Narwhal)

Question 7

7.3P
a) Name 4 terrestial (rocky) planets
b) Name 2 gas giants
c) Name 2 ice giants

Answer 7

a) Mercury, Venus, Earth, Mars
b) Jupiter, Saturn
c) Uranus, Neptune

Question 8

7.4P
Describe how ideas about the structure of the Solar System have changed over time

Answer 8

-Geocentric model -> Earth in centre Sun/planets orbits
-Naked eye: Sun/stars/planets revolve around us in same direc (same pattern everyday)

-Heliocentric model -> Planets orbit Sun
-Noticed planets/stars follow pattern throughout yr
-Sun didn’t (movement = slightly diff each day)

Question 9

7.4P
a) Describe the evidence for the geocentric model
b) Describe the evidence against the geocentric model (so for the heliocentric)

Answer 9

a) -Sun/moon/planets appear to move across sky in same direc -> look like orbit Earth
-Pattern was repeating

b) -Planets e.g. Jupiter have moons which orbit them -> not everything orbits Earth
-Sun movement slightly diff each day
-Planets can appear to move backwards (retrograde motion)

Question 10

7.5P
Describe the orbit of moons (natural satellites)

Answer 10

Elliptical

Question 11

7.5P
Describe the orbit of planets

Answer 11

Circular

Question 12

7.5P
Describe the orbit of comets

Answer 12

Elliptical

Question 13

7.5P
Describe the orbit of artificial satellites

Answer 13

Elliptical

Question 14

7.6P
What causes the earth to accelerate?

Answer 14

Gravity of the Sun

Question 15

7.6P
Explain for a circular orbit how the force of gravity can lead to changing velocity of a planet but unchanged speed

Answer 15

-Constant speed
-Changing direction
-So velocity is changing

Question 16

7.7P
a) How does the height of an orbit affect the gravitational force on the satellite?
b) How does this affect the speed it must move to stay in the orbit?
c) What would happen if the satellite slowed down?

Answer 16

a) Lower orbit -> greater F
b) If in lower orbit must be faster otherwise will get pulled in
c) Would move to higher orbit

Question 17

7.7P
Explain why objects with elliptical orbits don’t travel at constant speeds

Answer 17

As get closer to Sun -> More F acts -> faster

Question 18

7.7P
Why must the radius change if the orbital speed changes for a stable orbit to be possible?

Answer 18

Balance gravitational F (pulling object in) & centripetal F (keeping it in circular path)

Question 19

7.8P
Compare the Steady State and Big Bang theories

Answer 19

Steady State
-Matter constantly created -> Density always constant
-Universe always existed as it does now

Big Bang
-All matter started as tiny point
-Density of matter decreases over time

Both
-Space is expanding
-Universe started ~13.5 bill years ago

Question 20

7.9P
State 2 pieces of evidence that support the Big Bang theory

Answer 20

-Red-shift
-CMBR
(Cosmic microwave background radiation)

Question 21

7.10P
Which model for the origin of the universe is the most accepted and why?

Answer 21

-Big Bang theory
-More evidence

Question 22

7.11P
Describe the doppler effect

Answer 22

When source moves relative to observer -> change in λ & f of wave for observer

Question 23

7.11P
How does the pitch of a siren change for an ambulance driver?

Answer 23

It doesn’t

Question 24

7.11P
Explain how the sound of a siren changes as a fire engine passes an observer

Answer 24

-As approaches observer sound waves compressed (short wavelengths) -> ↑ frequency -> ↑ pitch
-As passes observer long wavelengths -> ↓ frequency -> ↓ pitch
-Doppler effect

Question 25

7.12P What is red-shift? How is it measured?

Answer 25

-Light shifts towards red end of spectrum -Change in wavelength

Question 26

7.12P What 2 things does a greater red-shift mean?

Answer 26

-Galaxies moving further away -Moving faster

Question 27

7.13P Explain how red-shift provides evidence for the Universe expanding

Answer 27

-Increase in red-shift -Shows GALAXIES moving away from Earth

Question 28

7.14P Explain how the red-shift of galaxies backs up both the Steady State theory and the Big Bang theory

Answer 28

-Shows galaxies moving away -SSt: new matter constantly created to maintain constant density as universe expands -BBt: Supports idea that universe expanding from single point

Question 29

7.15P Explain how the discovery of CMBR led to the Big Bang theory becoming the currently accepted model

Answer 29

-CMBR = radiation released at beginning of universe (Present wherever telescope is pointed) -Proves universe had **hot dense beginning** which has expanded since

Question 30

7.16P 7.18P Name the stages of the evolution of stars

Answer 30

Nebula -> Main sequence star -> Red giant -> White dwarf OR Nebula -> Main sequence star -> Red supergiant -> Supernova -> Neutron star or Black Hole

Question 31

7.16P Describe, in detail, the process a nebula goes through to become a white dwarf

Answer 31

-Nebula = cloud of gas -Gravity pulls gas together -> main sequence star -H₂ fusion -> heats -> pressure ↑ -> thermal expansion but gravity holds star together -> stable (continues for bill of yrs) -Eventually H₂ fusion runs out -> star cools -> collapses under gravity (bc outward F due to fusion is less than inward F due to gravity) which makes star hot again -Helium fusion makes star expand more -> red giant -Eventually fuel runs out -Gravity = bigger than thermal expansion -> star collapses -> tiny cold star (almost gives off no light)

Question 32

7.17P 7.18P Describe, in detail, the process a nebula goes through to become a neutron star or a black hole

Answer 32

-Nebula = cloud of gas -Gravity pulls gas together -> main sequence star -Star fuses -> heats -> pressure ↑ -> thermal expansion but gravity holds star together -> stable -Eventually H₂ fusion runs out -> star cools -> collapses under gravity which makes star hot again -Helium fusion makes star expand more -> red supergiant -Star goes through cycle of collapsing & expanding, helium nuclei fusing heavier metals each time (heaviest metal it can form is iron) -Thermal expansion reduces equilibrium -> star collapses -> rebounds on its centre (bc gravity is greater) -> star explodes -> supernova -After supernova, remains form neutron star or black hole

Question 33

7.18P Where is the only place elements heavier than iron can be produced?

Answer 33

In a supernova

Question 34

7.18P What is a neutron star?

Answer 34

-Neutrons densely packed due to gravity -Dense centre

Question 35

7.18P What is a key feature of a black hole?

Answer 35

Large gravity (not even light can escape)

Question 36

7.19P Most space telescopes orbit the Earth but the Spitzer telescope stays behind the Earth to hide from the Sun. Suggest why this is necessary

Answer 36

-Spitzer observes infrared (heat) -Infrared from Sun would overpower image

Question 37

7.19P Describe how methods of observing the Universe have changed over time

Answer 37

-Naked eye -Refracting telescope -Reflecting telescope -Technological advances allowed other parts of EM spectrum to be measured

Question 38

7.19P Why are some telescopes located outside the earth's atmosphere?

Answer 38

-Atmosphere absorbs some λ of light e.g. x-rays, gamma rays -Can't be detected from Earth -Allows to capture broader range of light