CBSE Class 9 Answered

Hi dear,

Submarines alter their buoyancy . Submarines have an inner and outer steel shell called a hull. The area in between the two hulls is called the ballast tank. ( As seen in the figure below).The ballast tanks can be filled with air or water. When submarine is on the surface, the ballast tanks are filled with air therby making the overall density of the less than the surrounding water.

To keep the submarine at certain depth, the crew adjust the mixture of air and water in seperate smaller ballast tanks. Now, the overall density is more or less equal to the surrounding water. This is called neutral buoyancy. 

An experiment for nutrientive value of grains is : pour a quantity of grins in apot of water ..if the major no. of grain sinks to the bottom, they still contain most of the nutrients. If the percentage of sugar in some cereals is higher, there is less room for the nutrients.

Hope this makes you clear.

Regards,

Aruna

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