1 d) astronomy

Question 1

1.22 understand gravitational field strength, g, and recall that it is different on other planets and the moon from that on the Earth

Answer 1

The strength of gravity on a planet or moon is called its gravitational field strength. But this force depends upon

• The masses of the two objects
• The distance between the masses

The greater the mass the greater the gravitional force. As the mass the mass in everyday objects are less, gravitional force is almost negligible. It is noticeable in planets, stars, sun etc.

Gravitational field strength of planets and moons

Mercury- 4
Venus- 9
Earth- 10
Moon- 1.6
Mars- 4
Jupiter- 23
Saturn- 9
Uranus- 9
Neptune- 11

Question 2

1.23 explain that gravitational force:

Answer 2

• causes moons to orbit planets
• causes the planets to orbit the sun
• causes artificial satellites to orbit the Earth
• causes comets to orbit the sun

Planets are held in orbit by the gravitional pull of the Sun. Similarly comets orbit the sun and moons and satellites orbit the planet. It is the gravitional attraction between this mass and each of the planets that holds the Solar System together and causes the planets to follow their curved paths.

Question 3

1.24 describe the differences in the orbits of comets, moons and planets

Answer 3

Comets: Comets orbit the Sun. Their orbits are very elongated. At times they are very close to the Sun , while at other times they are found at the outer reaches of the Solar System. As a comet gets close to the Sun, the gravitational forces acting upon it increase and it speeds up. At the opposite end of its orbit, a long way from the Sun, the gravitation forces are smaller, so the comet travels at its slowest speed.

Moons: Moons orbit a planet. The Earth has just one moon.The Moon, like the Earth spins on its axis, but much more slowly than the Earth turns. It completes one full rotation every 29.5 days. Because the time it takes to complete one orbit around the Earth is the same as the time for one rotation. The Moon always keeps the same part of its surface facing the Earth.

Planets: Planets orbit the Sun. The closest planet follows a much more tightly curved path than the furthest one. They all move in ellipses.

Question 4

1.25 use the relationship between orbital speed, orbital radius and time period:

Answer 4

The speeds of satellites vary greatly depending on the tasks they are performing. The speed of satellite can be calculated using the equation:

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

v= 2πr/T

Question 5

1.26 understand that:

Answer 5

• the universe is a large collection of billions of galaxies
• a galaxy is a large collection of billions of stars
• our solar system is in the Milky Way galaxy.

The Universe is mainly empty space within which are scattered large numbers of galaxies- astronomers believe that there are billions of galaxies in the Universe. The distances between galaxies are millions of times greater than the distances between stars within a galaxy.

Gravitional forces between stars cause them to cluster together in enormous groups called galaxies. Galaxies consist of billions of stars. Our galaxy is called spiral galaxy or the Milky Way and our nearest star is the Sun.