|
|||||||||||||||||||
|
|||||||||||||||||||
What a gas ...... Keep cool! ...... It droppeth from ...? ...... Gauge the Rain
Introduction
In this issue we look at a small selection of practical activities and investigations which may prove useful to
illustrate one of the Key Features in the National Guidelines for Environmental Studies at 5-14. A major relevant
attainment outcome for Science is Understanding Earth and Space and our chosen key feature - the physical
nature of the Earth, with particular reference to the role played by water ... in the Water Cycle. The first
set of these activities provides opportunities for work outside looking at aquatic environments where some of the
optical instruments discussed in
Newsletter 2
and
Newsletter 3
should come in handy.
| Water, water ...!
What is it? One glib answer is to tag water with its scientific formula H2O. A scientist's definition would probably go on to describe pure water as the normal oxide of hydrogen. This is a colourless, odourless liquid, boiling point 100 deg.C, melting point 0 deg.C and a maximum density at 4 deg.C of 1.000 grams per ml (or if you prefer, 1 gcm-3. That is the definition of pure water, not the water of the river or loch or for that matter the tap. Most of us know it as the liquid we use to make our tea or coffee, have a bath or dilute our whisky. But how would we feel if creatures such as those shown above were to be in the water we were drinking? | But is it clean?
Water like air is something we cannot live without. Like air there seems to be an unending supply, and both are subject to many forms of pollution. In many instances we need specialised equipment and measuring instruments to detect and measure any pollution present in a sample. With water there is a simple technique we can use to detect if quality is good or not so good. It is an environmentally friendly method and needs no sophisticated tools. Unlike the adverts for washing powders or liquids this is truly biological. Certain minibeasts can only live in unpolluted clean water, the water of our local reservoir or the bubbling mountain burn. Virtual Pond Dip - good web site |
| Taking samples
Remember to choose study areas with care. If taking samples no one should be allowed to drink the water and hands should be washed as soon as possible after visits to ponds or rivers. See section 13 of Be Safe! Minibeasts do not make good pets, unless you have an established aquarium or return them to their natural habitat. Eventually only the least environmentally demanding of creatures can survive. Of course in the river or pond the minibeasts would not be distributed with such an obvious split, some like the leech can be found in clean water as well as polluted water. Generally speaking, mayfly, stonefly and cased caddis are found in clean water, while worms, rat-tailed maggots and midge larvae are found in polluted water. Try a few samples from a local pond or stream. This should be carried out by the teacher and the sample taken from the bottom, including stones and mud. To view what has been captured empty the net into a large white pie dish. A hand lens of x2 magnification should provide sufficient power to see some of the beasties. Books and Kits
Adventures with Small Animals (ISBN 0 7195 3930 7) Also excellent was the old Streamwatch Kit with its posters and identification cards. As far as we know this is no longer sold - unless someone out there knows differently? |
| Clean river
| Some pollution
|
| Poor quality river
|
 |
 |
 |
A simple class
experiment to show evaporation of a liquid is to half fill two wide mouthed glass containers with water, large Pyrex
pudding bowls would be ideal, cover one with kitchen foil, leave the other uncovered. Mark the level of the liquid on
the outside of the bowl with an indelible pen or pencil. Stand the bowls on a window sill or near a heater.
Observe what happens to the level in each of the bowls. Are there any other noticeable signs? Make a record of the
levels over an agreed time period. Does the temperature of the surrounding air make any difference? What happens if we
try the same experiment with the bowls outside. Try a warm sunny day and a cloudy windy day. Are there a differences in
evaporation rates?
Keep cool!
| A home made refrigerator can provide further fun with evaporation Suppose we pose the
question :-
How can we keep or milk bottle or our drink-can cool if we don't have a fridge?
For this activity we need a bowl or basin, a small bottle, an terracotta flower pot and a stone. Half fill the bowl with
water, place a bottle with water in the bowl and put the flower pot over the bottle. The stone is used to seal the hole
in the top of the flower pot, To help speed up the process it is a good idea to soak the flower pot in water before
hand. To be more scientific we should devise an objective (fairer) test. One way would be to measure and record the temperature of the water in the bottle at the start of the experiment and perhaps take readings over an agreed period of time :-
|
| Condensation & evaporation
We have already hinted at some of the more likely answers, but another simple experiment will begin to show how water is returned from the air. Fill a glass with water and place in the refrigerator for a few hours, remove it and stand in a saucer. If this is done in the classroom it should take no more than a few minutes for a thin film of water to form on the outside of the glass. The warmer air of the classroom contains water vapour and this condenses on the cold sides of the glass. This can sometime be seen on the inside of the windows on a frosty morning. Is it seen anywhere else? Evaporation from rivers, lakes and puddles is one way that water gets into the atmosphere, are there any other ways? Why do the windows of the car sometime 'steam up' on a wet day? Why are the class room windows often covered with moisture? The answers from the class could be interesting, some will no doubt realise it could be from 30 people breathing in the enclosed space of the classroom. Now people breathing is not quite enough to replace the water content in the atmosphere to allow the rain to fall. Where else could it come from ? Could it be trees and plants? Is this one reason scientists are so worried about the destruction of the rain forests? We all know we have to water plants but what happens to that water? |
 |
 | How
do plants take up water?
Water is used by plants through their roots taking up nutrients from the soil to feed the leaf-producing parts. Some of the water is retained by the plant, the rest, you've guessed, is returned to the atmosphere. The figure opposite shows an interesting experiment. The flower in one vase has ordinary tap water, the other has the water coloured by a food dye. Choose white or light coloured flower heads and much darker food dyes. After a couple of days this shows that the plant takes water from the vase up to the flower head. On a warm day much of this water will be lost through evaporation. The biologists call this process transpiration.
|
Finally how do we measure the amount of
rain that falls? Here is one way.
This is the old lemonade bottle design. Carefully cut the top portion from the bottle as shown, invert it into the remaining part, glue a small ruler to the side, a rain gauge.
If the gauge is to be placed on a roof it will need to be placed in a tin with a hole in the bottom, weighted with sand or stones. If it is to placed on the ground it will need to be placed in a shallow hole to make sure it is not blown over.
