Describe the life cycle of a Star
- stars form from clouds of dust and gas - nebula
- a protostar is formed when gravity pulls the dust and gas together, there’s an increase in temperature and fusion takes place
- during fusion, helium nuclei fuse to make heavier elements
- a main sequence star is then formed and is stable as the force of gravity inwards is in equilibrium with the outwards pressure due to nuclear fusion - during this iron is formed
- a main sequence star then expands to form a red super giant (if bigger than the sun)
What is the orbital period?
Time it takes/ how long it takes to orbit an object
Why are satellites always accelerating?
- gravity causes satellite to accelerate towards the Earth
- speed is constant
- change in direction causes velocity to constantly change
- if velocity changes, it’s accelerating
What does it mean when ‘the universe seems to be expanding?’
Galaxies seem to be moving away from each other
How do we find that the wavelength has increased from distant galaxies?
We look at the light from most distant galaxies
What do we mean by the term red-shift?
- the wavelengths are all longer than they should be
- they’re shifted towards the red end of the spectrum
- this is called red-shift
What does red-shift suggest?
The source of the light is moving away from us
Measurements of the red-shift indicate that these distant galaxies are moving away from us (receding) very quickly
What does it mean when ‘more distant galaxies have greater red-shifts than nearer ones?’
More distant galaxies are moving away faster than nearer ones
How does instantaneous velocity affect the object whilst orbiting?
- object keeps accelerating towards what it’s orbiting
- but the instantaneous velocity (right-angled to acceleration) keeps it travelling in a circle
Where does the gravitational force need to be between for orbiting to occur?
- force that makes this happen is produced by the gravitational force
- which is between the planet and the sun (or between the planet and its satellites)
What does the size of the orbit depend on?
The object’s speed
Why does the size of the orbit depend on speed?
- The closer you get to a star or planet, the stronger the gravitational force is
- the stronger the force, the faster the orbiting object needs to travel to remain in orbit (to not crash into the object that it’s orbiting)
Describe what happens for an object in a stable orbit
- for an object in a stable orbit, if the speed of the object changes, the size (radius) of its orbit must do so too
- faster moving objects will move in a stable orbit with a smaller radius than slower moving ones
What is the solar system?
All things that orbit the sun
What are planets?
Large objects that orbit a star
What are dwarf planets?
Planet-like objects that orbit stars, but don’t meet all of the rules for being a planet
What is the moon an example of and what does it do?
Moons orbit planets. The moon is an example of a natural satellite (not man-made)
What are artificial satellites?
Satellites that humans have built (generally orbit the earth)
What force is needed to create orbits?
Gravity
How do planets orbit the sun?
Planets move around the sun in almost circular orbits
What does it mean if an object is travelling in a circle?
- if an object is travelling in a circle, it is constantly changing direction
- which means it is constantly accelerating
- also means it is constantly changing velocity, but NOT changing speed
What conditions must there be for an object to accelerate?
There must be a force acting on an object for it to accelerate
How does the force affect the object?
- force would cause the object to fall towards whatever it was orbiting
- but because the object is already moving, it just causes it to change direction
