First 498 words of the document:
How are stars formed? They are formed when gravitational attraction pulls
clouds of dust, rock and gas together, creating heat
that causes it to become hydrogen and then for the
hydrogen to fuse.
What happens to stars the size of our sun at the They expand to become red giants, then cool down and
end of their lives? collapse under their own gravity to become a white
What happens to stars at least four times the They expand enormously to become red supergiants,
size of our sun at the end of their lives? which then rapidly shrink and explode, realising
massive amounts of energy, dust and gas. This is
known as a supernova.
Name some properties of a neutron star. It only contains neutrons. It is very dense. It is formed
when a mediumsized star comes to the end of its life,
after it has become a supernova.
How big does a star have to be to become a It has to be greater than ten times the size of our Sun
black hole? (and is therefore a large star)
How are black holes observed? Indirectly, we observe their effects on their
surroundings, e.g. xrays emitted when gases from a
nearby star spiral into a black hole.
What is the turning effect of a force called? A moment
How can you increase the moment? You can increase it by increase the force applied or by
increasing the perpendicular distance between the line
of action of the force and the pivot.
What is the centre of mass of an object? It is the point through which the whole weight of the
When are the total clockwise moments and the When the object is not turning or is balanced.
total anticlockwise moments balanced?
When will an object topple? When the line of action of its weight (the force) is
outside its base.
Give an everyday example that uses centripetal Fair ground rides, spinning a ball on a piece of string,
force. planets orbiting sun
How can you increase the centripetal force acting Increase the mass of the object, increase the speed of
on an object? the object, decrease the radius of the object.
What provides the centripetal force for planets Gravitational force.
What shape are the orbits of the planets? Ellipses (or slightly squashed circles)
If the distance between two objects is doubled It becomes ¼ of the original force.
what happens to the force between them?
What is a communications satellite? It is a satellite that links different countries for TV, radio
and telephone. It's a geostationary satellite, meaning it
passes high above the equator and takes 24 hours to
orbit the earth, so it always stays on the same point.
Other pages in this set
Here's a taster:
What type of orbit does a monitoring satellite It has a low polar orbit (it passes continuously over the
have? North and South poles, so that the Earth spins beneath
Are the angles of incidence and angles of They are equal?
reflection equal or unequal?
What is the `normal' line? The `normal' line is perpendicular to the reflecting
surface at the point of incidence.…read more