#### Kerala PSC General Science Book Study Materials Page 15

Book's First PageLaw of Flotation Relative density or Specific Gravity It states that a floating object displaces its It is the ratio of the density (mass of a unit own weight of the fluid in which it floats. volume) of a substance to the density of a i.e. given reference material. Weight of floating object = weight of It is a dimensionless quantity, as it is the fluid displaced ratio of either densities or weights. Mass of floating object = mass of fluid RD subst an ce displaced reference Any changes in the density of the In SI units, the density of water is surrounding liquid affects the level in (approximately) 1000 kg/m3 or 1 g/cm3, which an object floats. which makes relative density calculations particularly convenient: the density of the Density (ρ) object only needs to be divided by 1000 or 1, depending on the units. It is its mass per unit volume. The symbol used for density is ρ. Viscosity (η) m V It is a fluid"s resistance to flow. Where ρ is the density, m is the mass, and Fluids become less viscous as the liquid"s V is the volume. temperature increases, becoming more Its unit is kilograms per cubic meter viscous as the fluid gets cooler. (kg/m3). A viscous fluid is sticky, thick and syrupy If we take a cubic centimeter of some to a greater or lesser extent. commonly known substances, we can see Its unit is the pascal second (Pa s) that they weigh different amounts: 1 pascal second = 10 poise = 1,000 millipascal second 1 centipoise = 1 millipascal second e.g. Treacle is quite viscous, but water is not. Hot engine oil is less viscous ("thinner") and runs more quickly and smoothly than cold engine oil. Bernoulli"s Principle So from the above examples it is easy to see that some of the cubes weigh more than others, It states that a rise (fall) in pressure in a even though they all take up the same amount flowing fluid must always be accompanied of space. by a decrease (increase) in the speed, and conversely, if an increase (decrease) in, Entity ρ (kg/m3) the speed of the fluid results in a decrease Interstellar medium (increase) in the pressure. * Assuming 90% H, 10% 1×10−19 It states that Pressure energy + Kinetic He; variable T energy + Datum or Potential energy = The Earth (Mean density) 5,515 Constant The Inner Core of the Earth 13,000 v2 p The core of the Sun 33,000–160,000 gz constant , where: 2 Super-massive Black hole 9×105 v is the fluid flow speed at a point on a White dwarf star 2.1×109 Atomic nuclei 2.3×1017 streamline, Neutron star 1×1018 g is the acceleration due to gravity, z is the elevation of the point above a Stellar-Mass Black hole 1×1018 reference plane, with the positive z- direction pointing upward – so in the 14

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