©John Parkinson

1

ICEBERGS

FLOAT ! WHY ?

©John Parkinson

2

mg

U

What can you say about mg and U?

What forces are acting on the iceberg?

3

IRON

MERCURY

DOES WOOD FLOAT?

DOES IRON FLOAT?

IT DOES ON MERCURY!

Why ??

Density Order: solid > liquid >>> gases

USUALLY ! !

kinson 4

BOX B SINKS BECAUSE THE BALLS ARE MORE D . . . . . Y PACKED

BOX A BOX BBOTH BOXES

CONTAIN BALLS OF THE SAME

MASS

ONE BOX SINKS WHEN IT IS PLACED IN WATER - WHICH?

DENSELY

VOLUMEMASS

DENSITY

UNITS ?? kg mkg m-3-3

n 5

VM

M

V

6

ICE IS SOLID WATER, so why does it float on water?

Is a liquid denser than a solid?

WATER IS MOST DENSE AT 40 C

Why does ice form on the top of a pond and

not on the bottom during cold weather ?

temperature / 0C

density / kg m-3

water

ice

992

1000Water density at

one atmosphere pressure

©John Parkinson

7

POND IN WINTER

Air at below zero

Ice at 00C

Water at 10C

Water at 20C

Water at 30C

Water at 40C

I bet its cold up there!

8

ARRANGEMENT OF MOLECULES IN WATER

ICE [SOLID WATER]

LIQUID WATER

STEAM

©John Parkinson

9

Archimedes’ Principle

“A body immersed in a fluid experience an

upward buoyant force [an upthrust] equal to the weight of the fluid

it displaces”

EUREKA !

Hence a floating body must displace its own weight of fluid”

U

mg

©John Parkinson

10The QM2 has a displacement

of 150 000 tonnes

11

UNITSHow many square centimetres in 1 square metre?

1 m

1 m 1 m2

100 cm

100 cm

1 m2 =

100 cm x 100 cm

= 10 000 cm2

Likewise 1 m2 = ? mm21 000 000

©John Parkinson

12

1m

1m

1m

1 m3 = 100 cm x 100 cm x 100 cm

1 m3 = 1 000 000 cm3

A cuboid has dimensions of 40 cm x 50 cm x 80 cm. What is its volume in cubic metres?

It is easier to work in metres from the start

0.40 x 0.50 x 0.80 = 0.16 m3

©John Parkinson

13

Again, because of its strength and density, depleted uranium is sometimes used in defensive plating on armored vehicles and other platforms to deflect ammunition

rounds that might otherwise kill or wound personnel inside the vehicle. It has been a component in munitions [ shell tips ] used against hostile tanks and other armored

vehicles.

DEPLETED URANIUMDEPLETED URANIUM

Depleted Uranium (DU) is what is left from natural uranium when most of the radioactive isotopes U234 and U235 have been removed. Depleted Uranium is forty percent less radioactive than the natural "background" uranium that is prevalent in the earth's air, water and soil. Depleted Uranium is hard and dense; it is almost twice as dense as lead.

What is DU used for?

Due to it density, [19050 kg/m3 ] depleted uranium is used in aprons to protect patients in hospitals and dentists' offices from excessive x-rays, and as ballast in 747 planes and in the keels of large sailboats.

©John Parkinson

14

General Relativity suggests that, as an object collapses to form a black hole, it will eventually reach a point of infinite density. This really means that the theory of relativity breaks down at

this point. We do not know what happens at the centre of a black hole. We need a theory of quantum gravity to predict

this.

What is the density of a black hole?