Physics – Key topic 8
4.8.1 Solar system; stability of orbital motions; satellites
4.8.1.1 – Our solar system
Within our solar system (which is a small part of the milky way galaxy – a massive
collection of billions of stars that are all held together by gravity), there is 1 star (the
sun), 8 planets and dwarf planets that orbit around the sun. There are also natural
satellites (the moons that orbit planets)
The sun
The sun was formed from a cloud of dust and gas (nebula) pulled together by
gravitational attraction. This collapsed under its own gravity, transferring GPE to KE in
its particles. As the nebula collapsed it became denser and rotated more rapidly.
Collisions between the particles caused kinetic energy to be transferred as internal
energy and thermal energy. The core of the nebula began to form a hot, dense
protostar. The sun’s heat evaporated ice and drove gas away from the inner solar
system, leaving rocks behind, which formed the planets
When the sun’s core became hot and dense enough, nuclear fusion reactions began
where:
- Hydrogen nuclei join together to form helium nuclei
- Energy is transferred by radiation
A star like the sun is in equilibrium – gravity tends to pull it inwards and radiation
pressure from the nuclear reactions tends to expand it outwards (the gravitational
collapse is balanced by the expansion due to fusion energy)
It is the largest object in the solar system. The sun’s huge gravitational field keeps
many other objects – planets, dwarf planets, asteroids and comets in orbit around it
Planets
As distance from the sun increases, temperature decreases and time taken to orbit
the sun increases
For a planet to form, its own gravity must be strong enough to make it round or
spherical in shape. Its gravitational field must also be strong enough to “clear the
neighbourhood”, pulling smaller nearby objects into its orbit
Moons
Moons are natural satellites that orbit a planet
Artificial satellites
Satellites that humans have built
Dwarf planets
, The gravitational field is not strong enough to clear the neighbourhood, so there may
be other objects in its orbit around the sun e.g. pluto
Asteroids
they orbit the sun in highly elliptical orbits. They are made of metal and rocky
material
Comets
Similar to asteroids, but are made of rocky material, dust and ice. They are frozen
rocks that move around the sun in elliptical orbits
4.8.1.2 – The life cycle of a star
The life cycle of a star is determined by the size of the star
Fusion processes in stars produce all of the naturally occurring elements. Elements
heavier than iron are produced in a supernova
- Nuclear fusion is a nuclear reaction in which two or more atomic nuclei collide at
nearly the speed of light and join to form a new type of atomic nucleus, creating
new elements
The explosion of a massive star (supernova) distributes the elements throughout the
universe
1. The force of gravity pulls a cloud of dust and gas together (a nebula). The particles
in the clouds are pulled together by their own gravity causing the particles to
speed up. The cloud merges together and becomes more and more dense forming
a protostar.
2. As the density of the protostar increases, its particles get faster and the
temperature increases so more particles collide with each other. Energy is being
transferred from the GPE of the protostar to its thermal energy store. When the
temperature gets high enough, hydrogen nuclei undergo nuclear fusion to form
helium nuclei. This gives out huge amounts of energy which keeps the core of the
star hot
3. The star enters a long stable period where the outward pressure caused by the
nuclear fusion that tries to expand the star balances the force of gravity pulling
everything inwards. These forces stay in equilibrium until most of the hydrogen
nuclei in the core have been fused together to form helium nuclei. This is called
the main sequence stage and lasts billions of years
- Energy released in the core keeps the core hot, so the process of fusion continues.
Radiation such as gamma radiation flows out steadily from the core in all
directions.
4.8.1 Solar system; stability of orbital motions; satellites
4.8.1.1 – Our solar system
Within our solar system (which is a small part of the milky way galaxy – a massive
collection of billions of stars that are all held together by gravity), there is 1 star (the
sun), 8 planets and dwarf planets that orbit around the sun. There are also natural
satellites (the moons that orbit planets)
The sun
The sun was formed from a cloud of dust and gas (nebula) pulled together by
gravitational attraction. This collapsed under its own gravity, transferring GPE to KE in
its particles. As the nebula collapsed it became denser and rotated more rapidly.
Collisions between the particles caused kinetic energy to be transferred as internal
energy and thermal energy. The core of the nebula began to form a hot, dense
protostar. The sun’s heat evaporated ice and drove gas away from the inner solar
system, leaving rocks behind, which formed the planets
When the sun’s core became hot and dense enough, nuclear fusion reactions began
where:
- Hydrogen nuclei join together to form helium nuclei
- Energy is transferred by radiation
A star like the sun is in equilibrium – gravity tends to pull it inwards and radiation
pressure from the nuclear reactions tends to expand it outwards (the gravitational
collapse is balanced by the expansion due to fusion energy)
It is the largest object in the solar system. The sun’s huge gravitational field keeps
many other objects – planets, dwarf planets, asteroids and comets in orbit around it
Planets
As distance from the sun increases, temperature decreases and time taken to orbit
the sun increases
For a planet to form, its own gravity must be strong enough to make it round or
spherical in shape. Its gravitational field must also be strong enough to “clear the
neighbourhood”, pulling smaller nearby objects into its orbit
Moons
Moons are natural satellites that orbit a planet
Artificial satellites
Satellites that humans have built
Dwarf planets
, The gravitational field is not strong enough to clear the neighbourhood, so there may
be other objects in its orbit around the sun e.g. pluto
Asteroids
they orbit the sun in highly elliptical orbits. They are made of metal and rocky
material
Comets
Similar to asteroids, but are made of rocky material, dust and ice. They are frozen
rocks that move around the sun in elliptical orbits
4.8.1.2 – The life cycle of a star
The life cycle of a star is determined by the size of the star
Fusion processes in stars produce all of the naturally occurring elements. Elements
heavier than iron are produced in a supernova
- Nuclear fusion is a nuclear reaction in which two or more atomic nuclei collide at
nearly the speed of light and join to form a new type of atomic nucleus, creating
new elements
The explosion of a massive star (supernova) distributes the elements throughout the
universe
1. The force of gravity pulls a cloud of dust and gas together (a nebula). The particles
in the clouds are pulled together by their own gravity causing the particles to
speed up. The cloud merges together and becomes more and more dense forming
a protostar.
2. As the density of the protostar increases, its particles get faster and the
temperature increases so more particles collide with each other. Energy is being
transferred from the GPE of the protostar to its thermal energy store. When the
temperature gets high enough, hydrogen nuclei undergo nuclear fusion to form
helium nuclei. This gives out huge amounts of energy which keeps the core of the
star hot
3. The star enters a long stable period where the outward pressure caused by the
nuclear fusion that tries to expand the star balances the force of gravity pulling
everything inwards. These forces stay in equilibrium until most of the hydrogen
nuclei in the core have been fused together to form helium nuclei. This is called
the main sequence stage and lasts billions of years
- Energy released in the core keeps the core hot, so the process of fusion continues.
Radiation such as gamma radiation flows out steadily from the core in all
directions.
