8.1 Solar System; Stability of Orbital Motions; Satellites

Give four types of object that form our solar system.

• Sun

• 8 planets

• Dwarf planets

• Natural satellites

What name is given to objects that orbit a planet?

Natural satellites

What is the name of our galaxy?

Milky Way

What is a nebula?

Cloud of dust + gas

How was the Sun formed?

From nebula pulled together by gravitational attraction

At the start of a star’s life cycle, what does the dust and gas drawn together by gravity cause, and what do these lead to?

• Fusion reactions

• Equilibrium between gravitational collapse of star and expansion of star due to fusion energy

At the start of a star’s life cycle, what is the dust and gas drawn together by?

Gravity

Why is the Sun white?

Emits all wavelengths of visible light equally

What are the eight planets in the solar system in order?

Mercury → Venus → Earth → Mars → Jupiter → Saturn → Uranus → Neptune

Describe the process of star formation.

• Particles in nebula pulled together by own gravitational attraction

• Nebula merge together (becomes more concentrated) — forms protostar

• Protostar becomes denser → its particles speed up more + collide more → temperature increases

  • process transfers energy from GPE → thermal energy

• Protostar becomes hot enough? → nuclei of hydrogen atoms fuse together — forms helium nuclei

  • energy released in this fusion → star is ‘born’

Describe what is meant by a protostar.

• First stage stars go through after forming from nebula

• Star becomes hot enough for hydrogen nuclei to fuse

In star formation, objects can form that are too small to become stars.

What happens to these objects?

Attracted by protostar → becomes planets orbiting star

Why do stars like the sun radiate energy?

Hydrogen fusion in core

What are stars like the sun called, and why?

• Main sequence stars

• Main stage in life of star

Explain why main sequence stars are stable.

• Forces within it are balanced

  • Gravity acts inwards trying to make star contract

  • Force f/ fusion reactions (radiation pressure) in core acts outwards trying to make star expand

• Forces are in equilibrium — stay in equilibrium until most hydrogen nuclei in core fused together to form helium nuclei

What is the life cycle of a star the size of the Sun?

Nebula → Protostar → Main sequence star → Red giant → White dwarf → Black dwarf

What is the life cycle of a star which is more massive than the Sun?

Nebula → Protostar → Main sequence star → Red super giant → Supernova → Neutron star or Black hole

What is a red giant star?

• Hydrogen used up and larger nuclei produced by fusion

  • stars of similar magnitude to Sun expand to form red giant

What produces all the naturally occurring elements?

• Fusion processes in stars

• Elements heavier than iron are produced in supernova

  • explosion of massive star (supernova) distributes elements throughout universe

What provides the force that allows planets and satellites to maintain their circular orbits?

Gravity

What is a satellite?

Object that orbits more massive object

What are artificial satellites?

• Man-made satellites that have been sent into space

  • for satellite imaging + communications

For circular orbits, the force of gravity can lead to changing velocity but unchanged speed.

Explain this.

• Gravity causes acceleration

• Acceleration = change in velocity

• Change in velocity = speed or direction changing

• In circular orbit, direction constantly changing → changing velocity + unchanged speed

Define radiation pressure.

Outward force cause by energy release f/ fusion

What is meant by the word ‘massive’ in the context of space physics?

Object w/ more mass

What effect does a resultant force have on an object?

Causes object to accelerate — change in object’s speed or direction

What is the only force acting on an object that is in orbit around a larger object?

Gravity

Explain why red giants expand.

• Main sequence star in equilibrium

• Hydrogen decreases → force from fusion reactions reduces

  • initially causes star to collapse inwards

• Inward collapse causes temp increase → allows helium nuclei to fuse together → makes heavier elements

  • outward force increases

• Star expands → becomes red giant

Describe how a white dwarf is formed.

• Red star becomes unstable

• Outer layer ejected and remainder collapses (because of gravity)

• Smaller v/ hot, dense solid core left behind (white dwarf)

What must an object do to maintain a stable orbit if it has a smaller orbit radius?

Travel at higher speed

Figure 1 shows the Hubble Space Telescope orbiting the Earth.

Explain the effect of the Earth’s gravitational force on the motion of the Hubble Space Telescope. [3 marks]

• Gravitational force causes Hubble Space Telescope to accelerate towards Earth

  • changes the direction of motion

• This changes velocity of Hubble Space Telescope

Galaxies contain billions of stars.

Compare the formation and life cycles of stars with a similar mass to the Sun to stars with a much greater mass than the Sun. [6 marks]

• All stars form in nebula by gravity → form protostar → fusion begins → fusion of small nuclei into larger nuclei

  • Become main sequence stars — stable period where gravitational forces inwards = outward forces due to fusion processes

• Stars about same size as Sun — expand to become red giant

• Stars bigger than Sun — expand to become red super giant

• Stars same size as Sun contract — temperature increases to become a white dwarf

• Stars bigger than Sun — explode in supernova

• Stars same size as Sun — cool to become black dwarf

• Stars bigger than Sun — become:

  • neutron star or black hole