ICEBERGS FLOAT ! WHY ? © John Parkinson

What forces are acting on the iceberg? mg U © John Parkinson What can you say about mg and U?

Why ?? IT DOES ON MERCURY! DOES WOOD FLOAT? DOES IRON FLOAT? Density Order: solid > liquid >>> gases USUALLY ! ! © John Parkinson

BOTH BOXES CONTAIN BALLS OF THE SAME MASS BOX A BOX B BOTH BOXES CONTAIN BALLS OF THE SAME MASS ONE BOX SINKS WHEN IT IS PLACED IN WATER - WHICH? BOX B SINKS BECAUSE THE BALLS ARE MORE D . . . . . Y PACKED DENSELY kg m-3 UNITS ?? © John Parkinson

M V  © John Parkinson

one atmosphere pressure Is a liquid denser than a solid? ICE IS SOLID WATER, so why does it float on water? temperature / 0C density / kg m-3 1000 Why does ice form on the top of a pond and not on the bottom during cold weather ? Water density at one atmosphere pressure ice water 992 WATER IS MOST DENSE AT 40 C © John Parkinson

POND IN WINTER I bet its cold up there! Air at below zero Ice at 00C Water at 10C Water at 20C Water at 30C Water at 40C © John Parkinson

ARRANGEMENT OF MOLECULES IN WATER ICE [SOLID WATER] LIQUID WATER STEAM © John Parkinson

Hence a floating body must displace its own weight of fluid” 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 ! U Hence a floating body must displace its own weight of fluid” mg © John Parkinson

The QM2 has a displacement of 150 000 tonnes © John Parkinson

UNITS How many square centimetres in 1 square metre? 100 cm 1 m 1 m2 = 100 cm 1 m 1 m2 100 cm x 100 cm = 10 000 cm2 1 000 000 Likewise 1 m2 = ? mm2 © John Parkinson

It is easier to work in metres from the start 1 m3 = 100 cm x 100 cm x 100 cm 1m 1 m3 = 1 000 000 cm3 1m 1m 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

DEPLETED 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. 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. © John Parkinson

What is the density of a black hole? 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. © John Parkinson