Copy each passage into your book and fill in the numbered gaps using the word bank. Then check your answers. This whole topic is Separate Physics only. ← All topics
1. Our solar system
Our solar system has one star, the Sun, plus eight (1)______, dwarf planets such as Pluto, and natural satellites called (2)______. Artificial satellites are made by people and put into orbit. Our solar system is a small part of the (3)______ Way galaxy. The Sun was formed from a (4)______ – a cloud of dust and gas – pulled together by (5)______.
Word bank: gravity · Milky · moons · nebula · planets
Check your answers
1 planets · 2 moons · 3 Milky · 4 nebula · 5 gravity
2. The life cycle of a star
As a nebula collapses, it gets hotter and forms a (1)______. When it is hot enough, hydrogen nuclei (2)______ to form helium. A main sequence star is stable for billions of years because the outward pressure from fusion energy (3)______ the inward force of gravity. A star about the size of the Sun becomes a red giant, then a white dwarf, then a (4)______ dwarf. A much bigger star becomes a red super giant, then explodes in a (5)______, leaving a neutron star or a black hole. Elements heavier than (6)______ are made in supernovae and spread throughout the universe.
Word bank: balances · black · fuse · iron · protostar · supernova
Check your answers
1 protostar · 2 fuse · 3 balances · 4 black · 5 supernova · 6 iron
3. Orbital motion
(1)______ provides the force that keeps planets and satellites in orbit. (HT) In a circular orbit the speed stays the same, but the (2)______ keeps changing, so the (3)______ changes – the object is accelerating towards the (4)______ of the orbit. For a stable orbit, if the speed changes, the radius must change too: a faster object needs a (5)______ orbit.
Word bank: centre · direction · gravity · smaller · velocity
Check your answers
1 Gravity · 2 direction · 3 velocity · 4 centre · 5 smaller
4. Red-shift and the Big Bang
Red-shift is an observed increase in the (1)______ of light from most distant galaxies. It shows that the galaxies are moving (2)______ from us, and the further away a galaxy is, the (3)______ it is moving. This is evidence that the universe is (4)______. The Big Bang theory says the universe began from a very small region that was extremely hot and (5)______. Since 1998, observations of supernovae suggest distant galaxies are moving away ever faster; scientists think this involves dark mass and dark (6)______, which are not yet understood.
Word bank: away · dense · energy · expanding · faster · wavelength
Check your answers
1 wavelength · 2 away · 3 faster · 4 expanding · 5 dense · 6 energy
