Transcript The Water Cycle

The
Water
Cycle
75% of Earth’s surface is covered with ocean.
25% of the surface is land (7 continents).
Maybe that’s
why Earth is
called the
Water Planet.
The
atmosphere
over all Earth
also contains
water in the
form of vapour.
But there are
two kinds of
water:
Salt water is in the oceans
Fresh water
is everywhere else
Most (97%) of the water on Earth is
salt water in the oceans.
Earth’s water
Salt water in the oceans
97%
Only
about 3%
of Earth’s
water is
fresh
water.
Fresh
water
3%
There are may types of plants and
animals that live in the salt water oceans.
But all the plants and animals that don’t live
in the ocean must have fresh (not salt) water
to live and grow.
Salt water from the oceans
becomes fresh water in a
process we call the…
Water
Cycle.
fresh water
Salt water
The water cycle begins when energy
from the sun heats ocean water.
This heat
energy
causes
evaporation.
evaporation -when liquid water
becomes vapor
Evaporation is what happens
when water “dries up.”
Water from the oceans is constantly
evaporating. Sunlight makes water
evaporate faster.
When water evaporates,
molecules of water become vapour
and float up into the air.
s
s
s
s
s
s
Only pure water can evaporate.
The salt stays behind in the ocean.
Some vapour gets into the air as it
is released from plants. This is
called transpiration.
Water vapour is not visible in the
atmosphere until it cools and
condenses into clouds.
condensation - when vapor
becomes liquid water
Condensation is the next part of
the water cycle where vapor cools
and forms clumps of liquid water.
Warm air can hold a lot of vapor but
when air cools the vapor condenses
into bigger and bigger droplets.
Vapor condenses more and more as it
gets cooler. Droplets get bigger and
clouds get darker.
When the droplets get too heavy
they fall to the ground as liquid or
frozen water. This step in the water
cycle is called precipitation.
precipitation - any water that
falls from the sky
(rain, snow, sleet, hail)
Precipitation is how the land areas
get fresh water that plants and
animals need to live.
Some of the precipitation falls as
snow. It may lay on the ground all
winter then melt slowly to keep
rivers running all summer.
Some precipitation falls as snow
and does not melt for many years.
Most of Earth’s fresh water is
stored in glaciers.
Some precipitation seeps down
underground to form aquifers.
We can drill wells to get this fresh
water.
aquifer
Some precipitation collects in lakes, and ponds.
Even if water is green, we call it fresh water.
Fresh doesn’t mean clean, it means not salty.
A lot of the precipitation runs off into
streams and rivers where it flows back to
the ocean. This is called runoff.
runoff
Precipitation that doesn’t soak into the
ground and “runs off” the land to get
back to the oceans.
Eventually, all fresh water
gets back to the ocean
where the cycle of
evaporation,
condensation,
precipitation
and runoff
can go on
and on to supply
fresh water to our planet.
A cycle is a wheel that is constantly turning
Earth’s water is
in a constant
cycle.
It evaporates
from the ocean,
travels through
the air,
rains down on
the land
and then flows
back to the
ocean.
Evaporation speeds up
when water is heated.
Earth’s atmosphere is warmer near the equator
where the Sun’s ray are more direct. The north
and south polar regions are colder.
cold
warm
hot
warm
cold
This is why the areas around the equator
where the world is hotter have more rain
and humidity.
equator
equator
Some parts of the world seem to be very dry,
but even in the desert, there is water.
Every living
plant and
animal
contains
water and
there is
water
vapor in
the air.
For millions of years, some
of the rain water that falls
has been soaking deep
underground. You can find
water in these aquifers
almost anyplace you drill.
Name 3 kinds of fresh water
Vapour
vay pohr
Water that is in the gas state.
Water molecules that have been evaporated.
Vapour is usually
invisible but hot
steam can be
seen for a few
seconds before
it disappears.
Dew
(doo)
Small droplets of water that appear on the
ground in early morning. Dew can occur even
with no clouds when humid air cools at night.
Many small animals get the water they need
from dew drops.
Convection current
Air movements
caused by
uneven heating
of the Earth
and
temperature
differences.
Hot air rises,
colder air sinks.
The result is
wind.
Aquifer
(ah kwih fur)
Big areas of underground water that can be found
by drilling almost anyplace on Earth. This is also
called the water table.
Drought (rhymes with out)
An usually dry period with less than normal
amounts of rainfall.
Flood
(flahd)
An usually wet period with more than normal
amounts of rainfall when rivers can’t carry the
runoff.
H2O
The chemical formula for water.
H2
+ O
(2 hydrogen atoms)
(1 oxygen atom)
water
( 1 water molecule)
Frozen H2O = ice
Liquid H2O = water
Gas H2O = vapor