density

It is the measure of the mass of a particular volume of substance.

formula for density

Density = Mass ------------ Volume

SI unit of density

kg / m³

CGS unit

g / cm³

1 g/ cm³

1000 kg/m³

measuring cylinder

It is a small glass vessel that measures the volume of liquid poured into it in ml. High accuracy

measuring beaker

it is a wide container used by milkmen to get rough estimates of volume. Low accuracy

Eureka can

It is a wide-mouthed container with a side opening called an overflow spout. it is used to find the volume of irregular solids via water overflow method. Low accuracy

how to find the volume of a cube

(side)³

how to find the volume of a cuboid

length * breadth * height

how to find the volume of a sphere

(4/3) * 3.14 * (radius)³

how to find the volume of a cylinder

3.14 * (radius)² * height

how to find density of an irregular object

1. find mass. 2. find volume via water displacement method. 3. divide mass by volume.

how to find volume using eureka can

first, fill the can with water till its spout. keep a measuring beaker under the spout. then, immerse the solid in it. the volume of water in the measuring beaker is equivalent to the volume of the solid.

relative density/ specific gravity

it is the density of a substance with respect to the density of water at 4*C.

relative density

RD = density of substance ---------------------------------- density of water or RD = volume of substance ---------------------------------- volume of water or RD = mass of substance ---------------------------------- mass of water

pycnometer

it is a small glass bottle with a glass cork. the cork has a capillary tube with a stopper to make sure the liquid does not spill out. the capacity is always fixed.

how to determine relative density of a liquid

we will use a specific gravity bottle/ relative density bottle/ pycnometer. first, measure the mass of the empty bottle. after that, fill the empty bottle with water, and insert the stopper so there is no extra water. then, measure the mass. after cleaning the bottle, repeat the process with the other liquid. then, calculate the mass of the liquid and water, then apply the formula.

hydrometer

it is an instrument that is made of glass, has a cylindrical stem, and a bulb weighted with either mercury or lead to make it float upright. when placed in liquid, it is lowered until it floats upright freely, and the point at which the liquid touches the stem will be its RD.

when will an object sink

if the RD > 1

when will an object float

if the RD < 1

law of flotation

it states that when a body floats in a liquid, the weight of the body is equal to the weight of the liquid displaced.

apparent weight of a floating body

0 [ as per law of flotation]

if a body floats in a liquid with density N, what will happen in a liquid with density 2N

in this case, the object will float with more of its portion outside the liquid.

force W

downwards force acting on the body [ weight ]

buoyant force

it is equal to the weight of liquid displaced by the immersed part

what happens when W = buoyant force

body will be under the liquid with the top just touching the surface.

what happens when Fb is greater than W

it will float with half its portion immersed in liquid

what happens when Fb is less than W

the body will sink.

balloons and flotation

balloons filled with helium float as helium is less dense than the air.

ice and flotation

it floats with a tenth of its part of water and the rest below water because ice has more spaces than water, making it less dense.

icebergs and flotation

90 % of the iceberg is actually submerged because of ice being lessdense than water.

people and flotation

it is easier for people to float in salt water than fresh water because the salts decrease the overall density of the body, making it float better.

iron ship and flotation

the ship has empty spaces containing air, which decreases the overall density to less than 1000 kg / m³

submarines and flotation

when submarines are going underwater, the tanks in the submarine are filled with water, so it gets pulled down. when it is coming back up, the tank is emptied, reduced the average density.

whales and flotation

whales have a special organ called an air bladder which helps them sink and rise. when coming to the surface, the bladder is filled with air, and when sinking, the bladder is filled with air.