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GRAVITY

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  Without gravity, we would fly off the spinning Earth and into space. Gravity is a force of attraction that acts between any two objects. The objects can be as large as galaxies or as small as subatomic particles. The strength of the gravity between two objects depends on their masses and the distance between them. Objects with large masses exert a strong force of gravity. Objects far apart attract each other weakly. CENTRE OF GRAVITY Every object consists of tiny particles of matter. Each of these particles has a small force of gravity acting upon it. Together, the forces act like a single force pulling downwards at just on point, called the centre of gravity. An object will balance when it is supported in line with its centre of gravity. Balancing is easiest if the object has a low centre of gravity. WEIGHT The force of gravity acting on an object is called weight. Like all forces, weight is expressed in units called Newton (N). An object's weight is directly related to its mass...
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OCEAN FLOOR

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  Far beneath the waves are the mountains, canyons, plains and valleys that make up the ocean floor. This underwater landscape, which is home to as fantastic a diversity of wild creatures as any continent, covers more than 60% of the earth's surface. New features are continually being added to the ocean floor as molten rocks wells up from the earth's hot interior through gaps in the Earth's crust. Once formed, these features change very little, because they soon become covered by protective layers made up of the remain of dead sea creatures that sink to the ocean bottom. SUBMARINE LANDSCAPE The ocean floor is really the entire seabed below the low-tide mark, but when people refer to the ocean floor . This is the part of the seabed that lies beyond the continental shelf. Most of the ocean-basin floor is more than 2000 m (6,500 ft) under the water. It is largely flat, but dotted with huge mountains called seamounts. Continental shelf is the gently sloping area between the edg...
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