Remember, as a member of the Science Bus Club you can ‘Ask Albert’ a question about any of the topics. So if you’re not already a member join today!!
Some Useful Words For You To Remember
Evaporation – when a liquid changes to a gas (also known as a vapour)
Condensation – when a gas (vapour) changes to a liquid
Boiling Temperature – the temperature at which a liquid boils. Water boils at 100 degrees
State – there are three states; solid, liquid and gas
Changing of State- this is when a substance changes from one state to another
More About Evaporation
Evaporation is the process by which molecules in a liquid state (e.g. water)
spontaneously become gaseous (e.g. water vapor). It is the opposite of condensation. Generally, evaporation can be seen by the gradual disappearance
of a liquid, when exposed to a significant volume of gas.
On average, the molecules do not have enough energy to escape from the liquid,
or else the liquid would turn into vapor quickly. When the molecules collide, they transfer energy to each other in varying degrees, based on how they collide. Sometimes the transfer is so one-sided that one of the molecules ends up with
enough energy to be considered past the boiling point of the liquid. If this happens near the surface of the liquid it may actually fly off into the gas and thus "evaporate".
Liquids that do not appear to evaporate visibly at a given temperature in a given
gas (e.g. cooking oil at room temperature) have molecules that do not tend to
transfer energy to each other in a pattern sufficient to frequently give a molecule
the "escape velocity" - the heat energy - necessary to turn into vapor. However,
these liquids are evaporating, it's just that the process is much slower and thus significantly less visible.
Evaporation is an essential part of the water cycle. Solar energy drives
evaporation of water from oceanslakes, moisture in the soil, and other sources
of water. In hydrology, evaporation and transpiration (which involves evaporation within plant stomata) are collectively termed evapotranspiration.
Below you can see a picture of water vapor that has evaporated off of hot tea
which condenses into visible droplets. Gaseous water is invisible, but the clouds
of water droplets are evidence of evaporation followed by condensation.
More About Condensation
Condensation is the change in matter of a substance to a denser phase, such as
a gas (or vapor) to a liquid. Condensation commonly occurs when a vapor is
cooled to a liquid, but can also occur if a vapor is compressed (i.e., pressure on
it increased) into a liquid, or undergoes a combination of cooling and compression. Liquid which has been condensed from a vapor is called condensate. A device or
unit used to condense vapors into liquid is called a condenser. Condensers are
used in heat exchangers which have various designs, and come in many sizes
ranging from rather small (hand-held) to very large.
Below you can see a picture of water on the outside of a cold glass on a hot day.
This is a perfect an example of condensation.
Why Do Puddles Dry Up?
Have you ever wondered why puddles disappear?
Well it’s because they evaporate. Puddles tend to evaporate quickly because of
the high surface area-to-volume ratio, allowing a large number of molecules
to be vapourised at once. As such they tend to be short lived.
Puddles that don’t evaporate are known as standing water.
Children love to splash about in puddles!!!!
More About Boiling
Boiling is the rapid d vaporization of a liquid, which typically occurs when a
liquid is heated to its boiling point, the temperature at which the vapor pressure
of the liquid is equal to the pressure exerted on the liquid by the surrounding environmental pressure. Thus, a liquid may also boil when the pressure of the surrounding atmosphere is sufficiently reduced, such as the use of a vacuum pump or at high altitudes.
Boiling occurs in three characteristic stages, which are nucleate, transition and
film boiling. These stages generally take place from low to high surface
temperatures, respectively.
Below is an image of some water that has reached it’s boiling point. Can you remember what that is? Make a note in you ‘zine’ as shown to you by Kieran, Albert’s assistant!!!
The Water Cycle
Water on earth moves in a continuous cycle, this is called ‘the water cycle’.
There is about the same amount of water on earth now that there
was when the dinosaurs roamed our planet!!!
How is this possible? Water travels to many places in many different ways. Where does it go and
how does it get there?
Run and get a glass of water and put it on the table next to you.
Take a good long look at the water. Now -- can you guess how old it is?
The water in your glass may have fallen from the sky as rain just last week, but
the water itself has been around pretty much as long as the earth has!
When the first fish crawled out of the ocean onto the land, your glass
of water was part of that ocean. When the Brontosaurus walked
through lakes feeding on plants, your glass of water was part of those lakes.
When kings and princesses, knights and squires took a drink
from their wells, your glass of water may well have been part of those wells.
The earth has a limited amount of water. That water keeps going
around and around in what we call the "Water Cycle".
This cycle as you already know is made up of a few main parts:
Evaporation (and transpiration) - Condensation
- Precipitation
- Collection
Below is a diagram showing the water cycle.
Some Cool Links
Click on any of the link buttons below to find out lots of more cool stuff about changing states.
Have fun!!!
Remember, as a member of the Science Bus Club you can ‘Ask Albert’ a question about any of the topics. So if you’re not already a member join today!!
