2. Physical Quantities and Measurement

Question 1

What are two main things found about density = mass/volume

Answer 1

• Equal masses of different substances have different volumes
• equal volumes of different substances have different masses

Question 2

what is the unit of density

Answer 2

unit of mass/ unit of volume

S.I - kg/m3
CGS - g/cm3

Question 3

How can density increase/decrease

Answer 3

(almost all substances expand on heating and contract on cooling, but their masses don’t change)

density decreases with the increase of temperature and increases with the decrease in temperature

Question 4

How does the density of water work (anomalous expansion of water)

Answer 4

Water contracts on heating from 0 °C to 4 °C (increases density)
Expands on heating above 4C (decreases density)

Question 5

What is the formula for:

Volume of a cube
Volume of a cuboid

Answer 5

(one side)^3

length x breadth x height

Question 6

What is the formula for:

Volume of a sphere:

Volume of a cylinder:

Answer 6

4/3 x pi x (radius)^3

pi(radius)^2 x height

Question 7

what is the formular for finding density (D)

Answer 7

D = M/V

Question 8

3 vessels used to measure volume

Answer 8

• Measuring cylinder (made of glass or plastic, graduated in mL, capacity is marked)
• Measuring beaker (made of glass or plastic or aluminium, used to take out a fixed volume of the liquid, capacity is marked)
• Eureka Can (glass or polythene or metal, it’s a beaker with a side opening near its mouth known as the spout)

Question 9

what is the principle behind the displacement method of measuring the volume of an irregular solid

Answer 9

a solid, when immersed in a liquid, displaces volume of liquid equal to it’s own volume

Question 10

how to determine density of a liquid

Answer 10

• measure it’s mass by a common beam balance
• measure volume by a measuring cylinder
• use formular (D=M/V)

Question 11

what is a density bottle (3)

Answer 11

a specially designed bottle which is used to determine the density of a liquid

it always contains the same volume of liquid each time it’s filled (usually 25 or 50mL)

since the density of water is 1 gm/cm3, the mass if water needed to fill the bottle completely will give the volume of the bottle

Question 12

what was the previous name of the density bottle

Answer 12

Specific gravity bottle

Question 13

what is relative density (2 Definitions)

Answer 13

the relative density of a substance is defined as the ratio of the density of the substance to the density of water

R.D
OR

relative density of a substance is the ratio of the mass of any volume of that substance to the mass of an equal volume of water

Question 14

what is the unit of relative density

Answer 14

just a number, no unit
ratio of the same quantities

Question 15

what is the density of a substance in g/cm3

Answer 15

the relative density of that substances

Density of substance in kg/m3 = 1000 x relative density

Question 16

what does specific gravity mean

Answer 16

it means relative density with respect to water

Question 17

how does density of a substance differ in different states of matter

Answer 17

solids are highly dense (molecules packed close together)

liquids are less dense and gases are the least dense

Question 18

what is exception to the ‘density in different states’ rule

Answer 18

density is ice is less than water

density of ice is 0.917 g/cm3 and water is 1.00g/cm3 and water vapour is 0.00057 g/cm3

Question 19

why do things float

Answer 19

a body floats on a liquid if it’s density is less than the density of the liquid while a body sinks if its density is more than the density of the liquid

Question 20

what is the principle of floatation

Answer 20

when a body is completely or partially immersed in a liquid, two forces act upon it

• weight of the body (W) acts vertically downwards (tendency to sink)
• buoyant force of the liquid (F’B) acts vertically upwards (move the body up)

Question 21

what is the buoyant force of the liquid

Answer 21

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

Question 22

what is buoyant force also called

Answer 22

upthrust (thrusts the body upwards)

Question 23

what are the three cases that happen in floatation

Answer 23

case 1: weight of the body (W) is greater than the buoyant force (F’B)

case 2: weight of the body (W) is equal to the buoyant force (F’B)

case 3: weight of the body (W) is less than the buoyant force

Question 24

Case 1 of Floatation (3)

Answer 24

• weight of the body W is greater than the buoyant force (F’B)
• resultant force is W-F’B which acts downwards
• body will sink in the liquid to the bottom under the resultant force

Question 25

Case 2 of Floatation (3)

Answer 25

- case 2: weight of the body (W) is equal to the buoyant force (F'B) - resultant force on the body is zero, i.e. the apparent weight on the body is zero - body will float just inside the surface of the liquid

Question 26

case 3 of Floatation (4)

Answer 26

- the weight of the body (W) is less than the buoyant force - The resultant force acts upwards - body will float partially above the surface of the liquid - while floating, F_B = W, so apparent weight is zero

Question 27

what is an important principle in case three of floatation?

Answer 27

only that portion of the body will be immersed in the liquid, by which the weight of the displaced liquid balances the weight of the total body

Question 28

what is the law of floatation (2)

Answer 28

when a body floats in a liquid, the weight of the liquid displaced by it's immersed part is equal to the total weight of the body weight of the floating body + weight of the liquid displaced by its immersed part

Question 29

what the weight of a floating body

Answer 29

according to the law of floatation, the apparent weight of a floating body is zero

Question 30

what are some applications of floatation? (7)

Answer 30

floatation of an iron ship floatation of man floatation of ice on water submarine icebergs whales balloons

Question 31

explain how an iron ship floats but an iron nail sinks (2)

Answer 31

- iron nail is completely solid and denser than water, this means Case 1 of floatation will act, and the resultant force is downwards - a ship is hollow and it's empty space contains air, making the average density of a ship less than that of water

Question 32

why is it easier to swim in sea water than in river water? (2)

Answer 32

- sea water contains salt and its density is more than river water density - weight of man gets balanced by the less immersed part of his body in sea water as compared to that in river water

Question 33

why does only a little bit of ice float on top of water while the rest floats inside (3)

Answer 33

- a piece of ice floats with its 9/10th part inside water and 1/10th outside - the reason: density of ice is 0.9 g/cm3 and water is 1.00 g/cm3 - weight of water displaced by 9/10th part of ice immersed inside water becomes equal to the total weight of the ice piece

Question 34

how can submarines rise and sink above and below water whenever desired? (3)

Answer 34

- submarine is a water-tight boat provided with water tanks - to made the submarine dive, tanks are filled with water so average density of the submarine becomes greater - to make the submarine rise, empty those taanks, average density decreases

Question 35

how do icebergs float? (2)

Answer 35

density of ice is less than that of sea water hence, iceberg floats with a large portion submerged inside and a little portion above the surface of the water

Question 36

how are icebergs dangerous for ships

Answer 36

since most of the iceberg is present beneath the surface of the water, a ship can collide with the invisible part of the iceberg

Question 37

how do whales float; dive and rise at their will (3)

Answer 37

- they have a special organ in their body called a swim bladder - they fill the bladder with air, decrease their average density and rise to the surface - to dive back into the sea, they empty the bladder, average density increases

Question 38

why do balloons float in air?

Answer 38

a hydrogen/helium filled balloon rises in air these gases are les dense than the density of air buoyant force experienced by air is greater than the weight of the balloon, pushing the balloon upwards