1.32 understand gravitational field strength, g, and recall that it is different on
other planets and the moon from that on the Earth
Gravitational field strength (g) is the strength of the force that pulls everything on a planet towards its gravitational centre. The gravitational field strength of the Earth is 10N/kg, while the gravitational field strength of the moon is about one sixth of this. This is because the Earth is larger than the moon and the larger the planet, the larger its gravitational field strength. So, planets smaller than the Earth such as Jupiter and Neptune will have a smaller gravitational field strength than the Earth and those larger than the Earth such as Venus and Mars will have a larger gravitational field strength.
1.33 explain that gravitational force
- causes moons to orbit planets
Planets are bigger and have a larger gravitational pull than their respective moons, so the moons orbit the planets because the pull is stronger and keeps them in their orbit.
- causes the planets to orbit the sun
The sun has is far larger than the planets in our solar system and therefore has a larger gravitational pull. This pulls on the planets and keeps them in its orbit.
- causes artificial satellites to orbit the Earth
The Earth's gravitational pull keeps artificial satellites in its orbit.
- causes comets to orbit the sun
The Sun's strong gravitational pull causes comets to orbit it. A comet's orbit takes it very close to the sun and then far away again.
1.34 describe the differences in the orbits of comets, moons and planets
- Comets have elliptical orbits around the sun, which bring them close to the sun where they speed up due to the gravitational pull and then further out into the solar system.
- Moons orbit around planets because the planets are larger and therefore have a stronger gravitational pull. They have elliptical (oval) orbits around their respective planets.
- Planets complete an elliptical orbit around the sun, due to it's larger gravitational pull.
1.35 use the relationship between orbital speed, orbital radius and time period:
orbital speed = (2 x π x orbital radius)/time period
Orbital radius = m (distance in metres)
Orbital speed = m/s (metres per second)
Time period = s (seconds)
1.36 understand that:
- 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 contains billions of galaxies. These galaxies contain many stars, each of which have a solar system. Our solar system is a part of the Milky Way galaxy.
