Topic 7

• Why does your weight vary across planets?

  ● Your weight is dependant on g, since weight =

  mass x g

  ● The gravitational field strength (g) of a planet

  varies depending on the size of the planet

  ● This means that your weight will also vary
• What is gravitational field strength on Earth?

  Approximately 10 N/kg
• What does our solar system consist of?

  ● The sun (our star)

  ● 8 Planets (Mercury, Venus, Earth, Mars,

  Jupiter, Saturn, Uranus, and Neptune)

  ● The planet’s natural satellites (ie. the moon)

  ● Dwarf planets

  ● Comets and asteroids
• Name the planets in order, starting with

  the closest to the sun.

  Mercury, Venus, Earth, Mars, Jupiter, Saturn,

  Uranus, and Neptune
• What did Ptolemy suggest about the universe?

  That the earth was at the centre. (Geocentric)
• What did Copernicus suggest about the

  universe?

  That the sun is at the centre and the

  planets orbit it. (Heliocentric)
• What did Galileo contribute to theories about the

  universe

  He used telescopes to support

  Copernicus’ suggestions about the

  sun, and suggested that moons orbit

  planets
• Describe the orbits of moons, planets, comets and

  artificial satellites.

  They orbit in an elliptical shape.
• Explain why for a stable orbit, the radius of orbit

  must change if the speed changes.

  ● At higher speeds, the object requires a greater

  centripetal force

  ● For a greater centripetal force, the

  gravitational force must increase

  ● This is achieved by the radius of the orbit

  being reduced
• Explain how the force of gravity acting on a satellite

  affects its speed and velocity

  ● The force can alter its velocity since the

  direction is continually changing

  ● It can’t cause a change of speed since

  there is no force component in the direction

  of motion
• Describe the Steady State theory

  The Steady State theory says that the

  universe has always existed but is

  expanding and creating matter to

  counteract the loss in density
• Describe the Big Bang theory

  The Big Bang theory states that the

  universe expanded from a very small

  dense point about 14 billion years ago.
• What is red-shift?

  A perceived increase in the wavelength

  of light due to the source moving away

  from the observer.
• What does red-shift provide evidence for?

  ● The universe is expanding

  ● This supports the Big Bang theory
• What does the Big Bang theory suggest?

  The entire universe started from a very

  small, hot and dense region in space.
• Compare the observed red-shift of two galaxies, one

  further away than the other

  ● The galaxy that is further away is

  travelling faster

  ● The observed red-shift is greater the

  further away it is
• What did scientists observe to provide evidence that

  the universe is expanding at an ever faster rate?

  They observed supernovae, which

  suggested that galaxies are moving

  away at an ever faster rate.
• Prior to observations of supernovae, what was

  believed about the rate of expansion of the universe

  and why?

  ● The rate of expansion was expected to

  occur more slowly

  ● It was thought that gravitational forces

  would cause this slowing down
• What does CMBR stand for?

  Cosmic Microwave Background

  Radiation
• What does CMBR provide further evidence for?

  ● The Big Bang Theory

  ● It is believed that CMBR originates

  from radiation produced in the big

  bang
• How does the existence of CMBR support the

  expansion of the universe?

  ● It is thought that gamma radiation was

  released in the Big Bang

  ● The expansion of the universe has

  stretched this radiation, resulting in the

  microwave radiation present today
• What factor determines the type of lifecycle a star undergoes?

  The size of the star
• What two phases do all the stars of the same or greater size than the sun undergo?

  Protostar phase and main sequence phase
• What do stars like the sun become at the end of their lifecycle?

  A black dwarf
• What two things can stars much bigger than the sun become at the end of their lifecycle?

  Neutron star or black hole
• What two phases do stars of similar size to the sun go through between being a main sequence star and a black dwarf?

  Red giant and white dwarf
• What two phases do stars of greater size than the sun go through between being a main sequence star and a neutron star/black hole?

  Red giant and supernova
• Describe the transition of the star from the nebula stage to the main sequence

  ● The nebula increases in size until it is pulled in due to its gravity, causing GPE to turn into KE

  ● The collisions between particles cause this kinetic energy to turn into thermal energy

  ● Eventually the nebula will become dense and hot enough to begin fusion (hydrogen to helium)
• What occurs in the stage when a star is a main sequence star?

  ● The fusion in the star releases energy

  ● This energy balances out with the gravitational potential energy leaving the star

  ● The star is in equilibrium so will not collapse due to gravity or expand due to radioactive behavior. It is stable.
• What happens when a star transitions to the red giant stage?

  ● Once all of the hydrogen fuel has been used up, the star begins to fuse helium and other larger nuclei

  ● This causes the star to expand and become a red giant
• How does a red giant become and white dwarf

  ● Once all reactions have taken place, the star's gravity pulls in all of its mass, making a small, dense white dwarf

  ● This will cool down to form a black dwarf
• Why are telescopes located outside the earth's atmosphere?

  ● The earth's atmosphere absorbs many electromagentic waves, making it difficult to detect certain waves

  ● Light pollution can make some images less clear

  ● Telescopes in space can operate both night and day
• What is the disadvantage of telescopes located outside the atmosphere?

  They are difficult to maintain as they have to be repaired in space (or brought down which is unreasonably expensive)
• What are the disadvantages of optical telescopes?

  ● They can only be used at night when the sky is clear

  ● They can't be used when the weather is cloudy etc.
• Evaluate the use of radio telescopes

  ● They are not weather dependant for example radio waves are not blocked by clouds so can be used in the rain

  ● They are usually large and expensive