Glossary

Anglo-Saxons

the

people

of

ancient

England

atmosphere

the

gases

that

surround

Earth

atomic

using

energy

from

atoms

crystal

a

type

of

rock

density

how

heavy

or

light

an

object

is

for

its

size

mercury

a

silvery-white

liquid

metallic

element

nautical

mile

a

unit

of

distance

used

mostly

by

sailors;

approximately

1 852

metres

radio

waves

invisible

waves

of

electromagnetic

energy

that

exist

all

around

us

speed

of

sound

how

fast

sound

travels;

approximately

1 191

kilometres

an

hour

standard

a

model

for

all

other

measuring

devices

supersonic

faster

than

the

speed

of

sound

ultrasonic

using

sound

waves

that

are

beyond

what

humans

can

hear