© john parkinson 1 icebergs float ! why ? © john parkinson 2 mg u what can you say about mg and u?...
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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
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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
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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!
©John Parkinson
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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
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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
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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
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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
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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?