Page 19 - Curriculum Visions Dynamic Book

The area of the Earth’s surface is 509,600,000 square km, of which 71% is ocean.
If you could weigh the Earth, it would have a mass of
6 x 1021 metric tonnes. Its density is, on average, 5.517 g/cm3 (although this average masks great differences between the very dense core and the much less dense crust).
The Earth’s magnetic field
The Earth has a powerful magnetic field produced by
the churning movements of its molten iron core. This magnetic field reaches far above the surface (see pages 20–21). That is a hugely important property because it traps electrons, protons, and other fast-moving particles, which could kill all living things if they reached the surface. The trapped particles form radiation belts around the Earth called the Van Allen radiation belts. It is these belts that are responsible for lighting effects over the poles called auroras (see pages 20–21).
centrifUgal force A force that acts on an orbiting or spinning body, tending to oppose gravity and move away from the center of rotation.
circUmference The distance around the edge of a circle or sphere.
core The central region of a body. electrons Negatively charged particles
that are parts of atoms.
gravitational field The region surrounding a body in which that body’s gravitational force can be felt.
gravity The force of attraction between bodies.
magnetic field The region of influence of a magnetic body.
mass The amount of matter in an object. molten Liquid, suggesting that it has
changed from a solid.
protons Positively charged particles from the core of an atom.
radiation The transfer of energy in the form of waves (such as light and heat) or particles (such as from radioactive decay of a material).
radiUs (pl. radii) The distance from the center to the outside of a circle or sphere.
satellite An object that is in an orbit around another object, usually a planet.
sphere A ball-shaped object.
tide Any kind of regular, or cyclic, change that occurs due to the effect of the gravity of one body on another.
 Here is the Earth seen with the Moon in about their correct proportions, the Earth being four times the diametre of the Moon. The gas giant Saturn and its rings, which combined are 21 times the diametre of the Earth, would fit inside the gap between the Earth and the Moon.
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