Water Pollution

Organic wastes such as sewage impose high oxygen demands on the receiving water leading to oxygen reduction with potentially severe impacts on the whole eco-system. Industries release a variety of pollutants in their wastewater including heavy metals, organic toxins, oils, nutrients, and solids. Discharges can also have thermal effects, particularly those from power stations, and these too decrease the available oxygen. Silt-bearing overflow from many activities including construction sites, deforestation and agriculture can inhibit the penetration of sunlight through the water column, restricting photosynthesis and causing blanketing of the lake or river bed, in turn damaging ecological systems.

Birds

Birds evolved from theropod dinosaurs during the Jurassic, and the initial known bird is the Late Jurassic Archaeopteryx, Ranging in size from tiny hummingbirds to the huge Ostrich and Emu, there are between 9,000-10,000 known living bird species in the world, making them the most diverse class of terrestrial vertebrates. Modern birds are characterised by feathers, a beak with no teeth, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a light but strong skeleton. Most birds have forelimbs customized as wings and can fly, though the ratites and several others, particularly endemic island species, have also lost the ability to fly.
Many species of bird undertake long distance annual migrations, and many more perform shorter more asymmetrical movements. Birds are social and communicate using visual signals and through calls and song, and contribute in social behaviors including cooperative hunting, helpful breeding, flocking and mobbing of predators. Birds are primarily communally monogamous, with meeting in extra-pair copulations being common in some species; other species have polygamous or polyandrous breeding systems. Eggs are regularly lay in a nest and incubated and most birds have an extended period of parental care after hatching.

Electric motor

An electric motor converts electrical power into mechanical energy. The reverse task, that of converting mechanical energy into electrical energy, is proficient by a generator or dynamo. Traction motors used on locomotives often perform both tasks if the locomotive is equipped with active brakes. Electric motors are found in household appliance such as fans, refrigerators, washing machines, pool pumps and fan-forced ovens.Most electric motors work by electromagnetism, but motors based on other electromechanical phenomenon, such as electrostatic services and the piezoelectric effect, also exist.
The fundamental principle upon which electromagnetic motors are based is that there is a mechanical force on any current-carrying wire controlled within a magnetic field. The force is described by the Lorentz force law and is vertical to both the wire and the magnetic field. Most magnetic motors are rotary, but linear motors also exist. In a rotary motor, the rotate part is called the rotor, and the stationary part is called the stator. The rotor rotates because the wires and magnetic field are arranged so that a torque is residential about the rotor's axis.