Topic 8 - The Universe Flashcards
the universe is a large collection of…
billions of galaxies
a galaxy is a large collection of…
stars
what force keeps stars together in a galaxy?
gravity
what does our solar system include?
planets, dwarf planets, moons, artificial satellites, asteroids and comets
what is a planet?
large objects which orbit a star
what is a dwarf planet?
planet-like objects which arent big enough to be planets
what are moons?
(natural) objects that orbit planets with a circular orbit
what are artificial satellites?
(man-made) objects that orbit Earth with a circular orbit
what are asteroids?
lumps of rock and metal which orbit the sun (commonly found in the asteroid belt)
what are comets?
lumps of ice and dust that orbit the sun - usually in highly elliptical orbits
how do planets orbit around the sun?
in almost circular orbits
what force causes planets to accelerate?
centripetal force acts towards the centre of the circle, causing the planet to change direction (therefore to accelerate)
what force keeps planets orbiting in a circle?
gravity causes instantaneous velocity to act at a right angle to the acceleration
