Space Physics
What's covered
Key facts
A star begins to form when gravity pulls together a cloud of dust and gas called a nebula, which contracts into a protostar.
Gravity provides the centripetal force that keeps a satellite or planet in a circular orbit, acting towards the centre of the orbit.
Light from distant galaxies is observed to be shifted towards the red (longer-wavelength) end of the spectrum, an effect called red shift.
Our Solar System contains one star, the Sun, which has eight planets orbiting it.
A protostar becomes a main sequence star when its core gets hot enough for nuclear fusion of hydrogen into helium to begin.
An object in a circular orbit moves at a constant speed but its velocity constantly changes because its direction is always changing.
The more distant a galaxy is, the greater its red shift, meaning more distant galaxies are moving away from us faster.
The Sun formed from a nebula, a cloud of dust and gas pulled together by gravity.
During the main sequence stage a star is stable because the outward pressure from fusion balances the inward force of gravity.
For a stable orbit at a fixed radius there is only one possible speed; if the speed increases the orbital radius decreases, so a faster satellite orbits closer in.
Sample questions
A taste of the 15 questions in this topic, answers marked. Sign up to practise the full set with spaced repetition.
What does a protostar become once nuclear fusion of hydrogen into helium begins?
- •A black hole
- ✓A main sequence star
- •A red giant star
- •A white dwarf star
What provides the centripetal force that keeps a satellite in a circular orbit?
- •Air resistance
- •Magnetic attraction
- ✓The pull of gravity
- •The push of thrust
What does the red shift of light from distant galaxies tell us about the universe?
- •The universe is contracting
- ✓The universe is expanding
- •The universe is rotating
- •The universe is staying the same size
What type of object is the Sun?
- •A comet
- •A moon
- •A planet
- ✓A star
Elements heavier than iron are formed only during the explosion of a supernova.
Answer: True
For a stable orbit, what happens to the orbital radius if a satellite moves at a higher speed?
- •Its orbital period increases
- ✓Its orbital radius decreases
- •Its orbital radius increases
- •Its orbital radius stays the same
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