CBSE Class 9 Answered

Dear student,

Buoyancy: The buoyant force is essentially caused by the difference between the pressure at the top of the object, which pushes it downward, and the pressure at the bottom, which pushes it upward. Since the pressure at the bottom is always greater than at the top, every object submerged in a fluid necessarily feels an upward buoyant force. Of course, objects also feel a downward force due to gravity, and the difference between the gravitational force and buoyant force on a submerged object determines whether that object will sink, or rise to the surface. If the weight is greater than the buoyant force, the object sinks, and vice versa. It was Archimedes (supposedly while in his bath), who realized that submerged objects always displace fluid upwards (the level of water in the bathtub rose when Archimedes got in). Thus, he reasoned that the buoyant force on an object must be equal to the weight of fluid that object displaces. If the weight of an object is greater than the weight of displaced fluid, it will sink, wherease if the weight of the object is less than the weight of displaced fluid, it will rise.

Archemedis principle: A solid object will sink in a fluid if its density is greater than the fluid's density and will float if its density is smaller.

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