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Middle Years Science Program
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Return to Science Shows  Program: Eloise Cole (St Joseph's). Presentation: Equipment:
Demonstrations:
Activities:
Websites: Storms Storms are quite frightening. A familiar occurrence in coastal Australia, storms form a very important component of our weather systems. Their violence is often destructive, their rain welcome and power awe inspiring. Severe storms are more common than any other natural hazard and they occur everywhere in Australia. On average, unclassified storms are responsible for more damage each year than tropical cyclones, earthquakes, floods and bushfires. Each year between 5 and 10 people are killed by lightning. Tornadoes have caused at least 41 deaths in Australia's short recorded history. A storm is produced when hot air and cold air mix, releasing huge quantities of energy and creating strong winds, rain, hail, lightning and thunder. Sometimes very large storms are driven by massive quantities of hot moist tropical air, these types of storms are known as cyclones in Australia or as hurricanes and typhoons overseas. Tropical cyclones occur in northern Australia during summer when the overhead Sun evaporates immense quantities of water creating huge reserves of stored thermal energy. The warm moist rising causes wind to blow in towards the centre of the storm while the rising air soon cools forming storm clouds and releasing some of the stored energy from the moist air. As more and more energy is released and more hot moist air is fed into the storm, it becomes larger and stronger eventually reaching proportions large enough to sustain itself and become a cyclone. Tropical cyclones soon die out when they move over land because the source of energy, moisture from the sea, is no longer available to drive the cyclone. Tornadoes Tornadoes occur when hot moist tropical air meets cold dry air. Tornadoes are especially well known over the southern states of the U.S.A. but also occur in Australia, mainly in south-eastern Australia. A tornado is a very violent windstorm in which the air whirls rapidly upwards in a vortex, forming a funnel shaped cloud. Tornadoes are associated with larger thunderstorm activity and form in the edges of the storm clouds and descend until they reach the ground. They can range in width from a few metres to hundreds of metres, their winds have been measured at more than 450 km/h. There is no generally agreed theory for the formation and maintenance of tornadoes, waterspouts, and other vortices. Eyewitness accounts associate particularly bright blue lightning in the eye of tornadoes and theories involve both electrical activity and the formation of circulating winds formed by the enormous energy released when large quantities of warm moist air are suddenly cooled when two air masses meet. The largest and most dangerous tornadoes definitely occur in the southern U.S.A. with over 1000 tornadoes recorded in some years. In Australia we quite often see much smaller vortices such as 'Willy-Willys', 'Dust Devils' or 'Whirl Winds'. Waterspouts are tornadoes that occur over water. The whirling air sucks up water creating a very well defined column of rising water. Fish caught in waterspouts have been known to fall to the ground many kilometres from the sea having been carried by the waterspout and associated storm. Lightning The lightning flashes that accompany thunderstorms are enormous electrical sparks caused when electrical charges build up in the storm clouds. Most lightning occurs within or between adjacent storm clouds. Friction within clouds created by updraughts and the movement of air creates the build up of negative and positive charge within a storm cloud. Lightning within clouds occurs when enough charge difference is built up and an electrical discharge jumps from a negative region to a positive region within the cloud. Lightning strikes from cloud to Earth occur slightly differently. Here negative charge build up within a cloud repels negatively charged electrons within the ground and induces (or creates) a positive charge on the surface of the Earth. Lightning will tend to strike the nearest place of accumulated charge on the ground, hence church spires, trees and even golf clubs can act as lightning conductors as they allow the accumulation of charge to occur. Lightning itself involves a 'leader' stream of electrons descending from the cloud towards the ground in a series of jagged steps and branches as it tries to find the path of least resistance. Once the lightning strikes the ground, it tries to dissipate its charge again along the route of least electrical resistance. This may be back up to the cloud along the original lightning strike path, so what at first appears to be a single movement of the lightning can actually be a series of rebounds back and forth between the cloud and the ground. The light from lightning is created as the electrons steaming along the lightning path, smash into and ionise molecules in the air making them emit light that we see as the flash. Thunder Thunder occurs when lightning dramatically heats nearby air, expanding the air very quickly. This creates an area of low pressure around the lightning flash. Upon cooling, surrounding air rushes back into the low-pressure zone. The sound we call thunder is created as part of the initial explosion of air and as the inrushing air meets again. Wind Strong winds are classified as 40-50km/h; 51-62km/h whole trees move; at 63 - 75 km/h gale winds break twigs from trees and you cannot walk; 76 - 87 km/h dislodged roofs and large branches break; storm occur at 88 - 102 km/h with trees uprooting and buildings damaged. Beyond 103 km/h, extensive and widespread damage to buildings and infrastructure occurs. Weather There is a number of different features that can be looked at regarding weather. Each of these can be monitored daily and trends can be discovered. A chart similar to the one below can be drawn up ...
Weather stations would conduct measurements of this kind on a daily basis. The weather patterns around Australia include ...
Composition
and Types of Soil: What is soil? It is a complex
mixture of minerals and organic matter. The minerals come
from the disintegrated rock, the organic matter from decomposed
plant and animal matter. Mixed in with this is water,
air and numerous living organisms. The main function of
soil is to provide plants with nutrients, water, oxygen
and anchorage for the root system. Soil is constantly
changing. Natural changes include the weather, insects,
worms, bacteria and fungi. Adding fertilizer, chemicals
and mulch can completely alter soil type. Most soil falls
into two categories: heavy or light depending on the amount
of clay or silt (fine particles) or sand (coarse particles)
they have. Clay is made from very fine particles that
pack together closely, thus hindering the downflow of
water and air which are both essential for plant growth.
Gypsum can break this up and allow the plant to take in
water and air.
In clay soils in a large downpour, plant root may end up very wet and stay wet resulting in the rotting of tree roots - the spaces between clay particles are filled with water. Sandy soils are light because they are much easier to dig when wet or dry. Sandy soil drains faster but they may dry out too fast.Sany soils must be have rainfall more frequency. They must also be fertilized more often since their nutrients wash away quickly. Loamy soil is half way between the two and is ideal for plants. To identify soil types, follow the steps below ...
Rotation
of the Earth & Formation of Wind: The
spinning Earth on its axis as it passes from day to
night and back to day is largely the cause of our wind
currents on the surface of the Earth. The winds are
somewhat stationary within a spinning planet surface.
Only sometimes when we see the clouds moving past us
can we make predictions as to the direction the Earth
is spinning ... it is usually a lot more complicated
than that. Areas of high pressure air (and weather)
push towards areas of low pressure air resulting in
the seemingly never endless change in weather patterns
the world experiences. Storm fronts occur when air fronts
of different air pressure meet and force one of the
fronts upwards. The resulting increase in altitude forces
this air to release any excess water vapour it is carrying
in the form of clouds.
Air can only support a certain amount of water vapour. If it rises further into the air or is shaken around it will release some of this water vapour ... ie. it will begin to rain. Rapid movements of different weather fronts can cause such disasters as cyclones, tornadoes and storms. The other feature of weather could result from gravitational forces from the Moon. The Moon provides a huge amount of gravitational force on objects on our planet. When we drop objects they fall towards the ground; when we jump off a ladder we fall over. This force is due to the very nature of massive objects to contain mass. The more particles that exist within 2 different objects, the more force of gravity occurs between them. Since in our immediate area the 2 largest objects are Earth and the Moon it is understandable that the Moon creates a huge effect on objects on the Earth. In fact, the attractive force of the huge bodies of water (oceans, seas etc) towards the Moon create the high and low tides we experience. As a result you might expect at high tide the Moon to be directly above. Weathering: Look around at the landscape in your area. Whether you see mountains, plains, river valleys, coasts, islands, lakes or ocean, what you see is the product of the constant changing of the Earth's surface.
Mountains are pushed up from the plains. Islands form. New land is created by volcanic action, caused by the collision of tectonic plates and by the uplift of shallow sea beds. Over thousands and millions of years, the twin processes of weathering and erosion will flatten the mountains, extend the plains and wash the highest peaks back to the ocean floor. What is weathering? Weathering is the constant wearing away and the decomposition of the Earth's surface. Rain, wind, ice, plants, animals, the temperature and chemicals all play a part in breaking down the rocks into smaller particles which form the basis of soil. There are two categories of weathering; mechanical weathering and chemical weathering. Each involves different mechanism of weathering. Mechanical weathering: Mechanical weathering involves the breakdown of rock to smaller pieces by mechanical or physical means. The main types of mechanical weathering are: Ice wedging: If the air temperature drops below the freezing point of water, any water caught in a crack in a rock will expand upon freezing. This can cause the rock to crack even more and can even break off large chunks of rock starting the process of erosion. Temperature change: The Sun warming up the surface of a rock will make the rock's surface expand. The underlying rock remains cold and does not expand. At this point, the surface rock may split from the underlying rock, making it vulnerable to further weathering and erosion. Plants and animals: The growth of plant roots in cracks in the rock and animals burrowing around the rocks, allows water to enter the rock and it surrounds again making the rock vulnerable to further weathering and erosion. Both these processes accelerate the breakdown of rock surfaces. Water: Rivers and streams carrying small rocks and mud act as abrasives on rock surfaces, wearing away the rocks in their path. Wind: Wind carries sand which can impact surface rocks and sand blast them forming more sand and dust. Chemical weathering: Changes in the chemical composition of a rock will often weaken it structurally, making it more vulnerable to mechanical weathering. Chemical weathering occurs when air, water or acids react with rock to change its chemical composition. The main types of chemical weathering are: Water: Rain falling on a new rock surface will remove some elements from the minerals forming the rock. This process, known as "leaching", can dramatically alter surface rock, allowing it to become more prone to mechanical weathering. Oxidation: Iron left out in the weather soon rusts. Other elements within the rock minerals will also react with oxygen in the air, quite often forming water-soluble minerals that can then leach away. Carbonation: Rainwater combines with carbon dioxide in the air to form a weak acid known as carbonic acid. This acidic solution is particularly effective in weathering limestone and marble. Some limestone caves and sinkholes are thought to have been formed by the constant action of carbonation over thousands and millions of years. Plant acids: Some plants and fungi produce acids that dissolve the surface of rocks and minerals to help their roots gain a hold in the rock. Acid rain: Acid rain has been a part of the environment for about 4.5 billion years. Before the industrial age, it was a result of the interaction between sulfur from volcanoes and water in the atmosphere and in rivers and oceans. The industrial age has brought with it an increase of acid rain, now produced by sulfur dioxide being released when coal and oils are burnt. Acid rain can be a very strong acid, killing fish and accelerating the destruction of man made monuments and rock alike. The strong acids dissolve elements from minerals in the rock, altering the surface of the rock in much the same way. Once weathering has weakened the structure of rocks, the process of erosion can now take place. Weathering structurally weakens the rocks, while erosion removes and transports the weathered material. Erosion: Once rocks have been broken down by mechanical and chemical weathering, the resulting particles are now smaller, and able to be picked up and transported. The process of picking up and moving weathered rock materials is called erosion. The process of dropping these materials in a new place is called deposition. Erosion occurs when rock particles are moved by an external force or agent. The agents of erosion are ice, water, wind, waves and gravity. The degree to which erosion occurs depends on the slope of the land, amount of rain or snow, wind and looseness of the rock and soil. The hills of Australia no longer erode quickly, but the steep mountains in the New Zealand Fjord country tend to erode very quickly. On the slopes of Mt. Cook, New Zealand, you can hear the mountains eroding as rocks slip and roll down the steep sides of the glacial valleys. The five agents of erosion will now be further investigated. Gravity: Whether a whole mountain side moves slowly or a landslide occurs quickly and dramatically, the mass movement of rocks and soil under the influence of gravity can remove large amounts of material from a mountain side. Often associated with rain, which weakens a slope, gravity is an important agent of erosion in high steep mountains. In areas which have been cleared of trees, land movement becomes a real threat. The foothills of the Himalayan mountains of India and the Andes in South America both have large populations trying to cultivate the steep hill sides. In recent years, huge mud slides have caused mass destruction of villages and the flooding of low land areas. Authorities are now working to stop the threat of land slides by reforestation and the ban on removal of trees from these areas. Water erosion: Rain falling on bare soil on a slope can result in the soil breaking free from the underlying rock and flowing downslope, carrying mud and rock within a mud flow. From the peaks of the mountains, running water forms streams in gullies and canyons. Water is the most important agent of erosion in wet highland areas, quickly moving large quantities of material into lower river valleys and plains. The removal of trees and their replacement with agriculture has lead to a significant increase in the loss of topsoils in Australia via water run off. Planting of trees around water ways and in areas of high risk from water erosion and better farming practices can significantly decrease the amount of soil lost to water erosion. Ice erosion: In colder regions, where snow is the predominant form of precipitation, glaciers are the most important agent of erosion. The action of ice, although slow, can be dramatic. The heavy, slow moving ice carries rock, pebbles and sand, which is then trapped within the ice. These trapped rocks ground away at the base and sides of the glacial valley like gigantic sand paper. During the last ice age, glaciers flattened whole mountains in Tasmania, leaving behind the large lakes of the Tasmanian Western Highlands. On the South Island of New Zealand, steep sided valleys have been formed by glaciers with cliffs hundreds of metres high. Wind erosion: In dry areas, wind becomes the primary agent of erosion. Sand storms and wind are responsible for the movement of finer dust and sand producing the dominant features of desert landscapes; plains, dunes and sculptured rock outcrops. Over many parts of Australia, the agricultural practice over the last 200 years has involved the removal of many trees from arid regions. This exposes the soil to the wind and increases the chance of dust storms occurring, like the one that occurred over Melbourne in 1983. Wave erosion: A visit to any beach with a cliff will soon attest to the power of waves as agents of erosion. Coastlines are continually being sculptured and shaped by the action of waves. The Twelve Apostles in Western Victoria with their cliffs, stacks, arches and caves are the classic example of a landscape created by wave erosion. These structures are formed as softer rock is eroded away more quickly than harder sections leaving some parts out in the ocean as the cliff lines slowly recede under the pounding of the waves. After weather and erosion have affected the landscape, the next step is deposition, as the eroded and transported material comes to rest.
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