Astrophysics - Motion in the Universe

Question 1

what is the universe?

Answer 1

a large collection of billions of galaxies

Question 2

what is a galaxy?

Answer 2

a large collection of billions of stars

Question 3

what is our solar system?

Answer 3

the milky way galaxy

Question 4

why does gravitational field strength vary?

Answer 4

• an object’s gravitational field strength (g) depends on its mass
• a large object will have a very large g
• the Moon has less mass than the Earth, so its g is much weaker
• a planet with a large radius will have a weaker gravitational field at its surface because the surface is further away from the centre of the planet

Question 5

what does gravitational force cause?

Answer 5

• moons to orbit planets
• planets to orbit the sun
• artificial satellites to orbit the earth
• comets to orbit the sun

Question 6

what are the differences in the orbits of comets, moons and planets?

Answer 6

• comets have highly elliptical orbits, with the Sun at one focus. when they come in close to the Sun they speed up, due to the larger gravitational force on them
• moons have circular orbits
• planets orbit in ellipses

Question 7

what is the relationship between orbital speed, orbital radius and time period?

Answer 7

orbital speed = (2 x pi x orbital radius)/time period