Which nuclear reaction powers a star like our Sun and how does it work?
Fusion - light nuclei (hydrogen) are joined to produce heavier nuclei (helium) , releasing energy in the process due to the conversion of a small quantity of mass into energy
Which force is responsible for making mass attract mass, and is it a contact or a non-contact force?
Gravitational attraction, Non-contact force
What is a nebula?
A large cloud of gas and dust
When small nuclei fuse, what is always released?
Electromagnetic radiation
The birth and life of a star
- The fusion reaction becomes self-sustaining, which means it continues to happen by itself, and the star continues to shine because it is emitting electromagnetic radiation
- Eventually the radiation pressure outwards balances the gravitational force inwards
- The star is now a main sequence star and the star is in stable equilibrium. When the radiation pressure outwards and gravitational force inwards balance out, the star sustains its fusion reaction for billions of years
In what stage of a star’s life cycle does fusion occur?
Main sequence
The death of a low mass star
- When the star runs out of hydrogen nuclei to fuse together in its core, there is not enough to sustain equilibrium and it reaches the end of its main-sequence stage
- Its core collapses, and its outer layers swell down
- Stars about the same size as the Sun (or smaller), swell out, cool down and turn red
- These stars are now red giants
- The red giant then sheds some outer layers (which can go on to make new planets) and shrinks down to become a white dwarf, a planet sized, very hot body in the same location as the original star
What is an orbit?
The curved path taken by a moving body around another larger body, due to mutual gravitational attraction
What is the Earth in orbit around?
The Sun
What orbits the Earth?
The Moon
What is the difference between speed and velocity
- Speed is a scalar quantity, and only has magnitude
- Velocity is speed in a given direction, it is a vector quantity so has both magnitude and direction
Factors affecting orbits
- Direction of the velocity
- Direction of the gravitational force
What is the red-shift?
An observed increase in the wavelength of light from distant galaxies
How does the red-shift provide evidence for the Big Bang?
- Provides evidence that the universe is expanding
- Supports the Big Bang Theory
What is the Big Bang theory?
- All the matter in the universe was squashed into a tiny space
- The matter was thrown out very suddenly and very quickly, like an explosion
- All the energy in the universe formed matter
- The universe is getting bigger and bigger all the time. It is currently expanding
Why do stars in outer galaxies appear red?
- As the distance between the observer and outer galaxies increases, the wavelength of light emitted by these outer galaxies increases, whilst the frequency of the waves decrease
- Red light has a longer wavelength and lower frequency, so the wavelengths of light shift towards the red end of the EM spectrum
- The stars are moving away from us, so they appear to be red
Explain how this observation supports the Big Bang theory of the formation of the universe
- The furthest galaxies show the biggest red shift
- Meaning that the furthest galaxies are moving fastest
- So the universe is expanding
- The Universe started from an initial point (The Big Bang theory)
Explain why in circular motion (like orbits) the body is accelerating
- Acceleration is the change in velocity divided by time
- The resultant force due to gravitational attraction is always changing the direction of the orbiting body
- Since the direction is changing, the velocity is constantly changing
- The magnitude of the velocity remains constant but since the direction is changing, the velocity is changing
What is CMBR?
Cosmic microwave background radiation
What is the evidence to support the Big Bang theory?
CMBR and Red-shift
Explain why the star is stable while it is in the main sequence stage of its life cycle
The gravitational force inwards and forces as result of fusion reactions outwards are in equilibrium
Describe what will happen to a star, the same size and mass as the Sun, between the main sequence stage and the end of the star’s life cycle
- The star will expand to become a red giant
- The star will collapse to become a white dwarf
- The star will cool to become a black dwarf
What is in our solar system?
- One star, the Sun
- Eight planets
- Dwarf parents
- Natural satellites called moons that orbit planets
Explain how the sun and solar system was formed
- The universe contains clumps of dust and gas each called a nebula
- Gravitational attraction pulls this dust and gas together
- Forming the Sun
- Fusion reactions lead to an equilibrium between the gravitational collapse of the star and the expansion of a star due to fusion energy
- The remaining parts of the solar system form from the remaining dust and gas
