What our solar system contains, how gravity keeps objects in orbit, and why an object in a circular orbit accelerates even at constant speed. Physics only content.
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1.What is at the centre of our solar system?
The Sun, which is a star.
2.Name the objects that make up our solar system.
The Sun, the eight planets and their moons, dwarf planets such as Pluto, asteroids and comets.
3.What is a planet?
A large object that orbits a star and has cleared other objects out of its orbital path.
4.What is a dwarf planet?
An object that orbits a star and is large enough to be roughly spherical, but has not cleared its orbital path.
5.What is a moon?
A natural satellite that orbits a planet.
6.What is our solar system part of?
The Milky Way galaxy.
7.What is a galaxy?
An enormous collection of stars held together by gravity.
8.How did the Sun form?
A cloud of dust and gas, called a nebula, was pulled together by gravitational attraction.
9.What force keeps a planet in orbit around the Sun?
Gravity, acting towards the Sun.
10.In which direction does the gravitational force act on an orbiting object?
Towards the centre of the object it is orbiting.
11.What happens to the velocity of an object in a circular orbit?
Its direction changes constantly, so its velocity changes even though its speed does not.
12.Why is an object in a circular orbit accelerating?
Acceleration is a change in velocity, and its direction is continually changing.
13.Does the speed of an object in a stable circular orbit change?
No. Only the direction changes.
14.What is needed for a stable orbit at a particular radius?
The object must travel at one particular speed for that radius.
15.What happens if an orbiting object speeds up?
It moves into an orbit of larger radius.
16.What happens if an orbiting object slows down?
It moves into an orbit of smaller radius.
17.How does orbital speed change with distance from the Sun?
Planets further from the Sun travel more slowly in their orbits.
18.Why do planets further out take much longer to orbit?
They travel more slowly and have a much greater distance to cover.
19.What is an artificial satellite?
A man-made object placed in orbit around a planet, used for communication, observation or navigation.
20.Why does a satellite not fall to Earth?
It is falling, but it also moves sideways fast enough that it continually falls around the Earth rather than into it.
21.What shape are the orbits of the planets?
Slightly elliptical, though close enough to circular to be treated as circles at this level.
22.What are comets and how do their orbits differ?
Icy bodies that follow highly elliptical orbits, taking them very close to the Sun and then far out again.
23.Why does a comet speed up as it approaches the Sun?
The gravitational force is stronger when it is closer, so it accelerates as it falls inwards.
24.What would happen to a planet if the Sun suddenly disappeared?
With no force towards the centre, it would travel in a straight line at constant velocity.
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