MadSci Network: Other

Re: Will ice cubes float in all liquids?

Date: Fri Feb 22 10:07:14 2002
Posted By: Thiam Hock, Tan, Secondary School Teacher, Science, Dunman High School
Area of science: Other
ID: 1013005401.Ot

Dear Kayla:

No. Ice cubes do not float on all liquids. For example, if you place your 
ice cube in a cup of light oil (thin cooking oil. Don't use heavy greasy 
oils), it will sink.

Why do things float on water? This has to do with something known as 
bouyancy. It's because of bouyancy that ships can float on water, 
as can corks and other things. It's also the reason that Archimedes ran 
out of his bath naked screaming 'Eureka!' all those years ago. 

Think about a tub of water or a swimming pool. If you push your hand in, 
the deeper you go, the harder the water pushes on your hand, because the 
deeper you go, the more water there is above you that's weighing down on 
you. Same with air. If you climb high into the mountains, there is less 
air over your head, so it doesn't push on you quite as hard any more. This 
is the reason your ears pop when you go very high very fast. The 
pressure of air in your ears is different from that of the air 
outside, and it is released in a 'pop'.

Ice cubes float on water because it is less dense than water. 
Density measures how much mass there is per volume. For example, if you 
have a metal cube and a plastic cube of the same volume (same length, 
width, and height -- same size), the metal cube is denser than the plastic 
cube. Most people would say 'the metal cube is heavier', and that's 
because it's more dense, so there's more matter per unit of volume than 
the plastic cube.

When an object, like an ice cube, is placed in water, the water pushes 
against the object, this is called 'exerting a pressure on the object'. 
his pressure can come from below as well as from above. If you're not 
using water, and use honey or some other liquid that is denser than water, 
the pressure will be higher. If you use oil or some liquid that is less 
dense than water, the pressure will be less. The object itself has a 
weight, and is being pulled downwards by gravity. The more mass the object 
has, the more strongly it is pulled downwards by gravity. If the downward 
pull of gravity is greater than the upwards push of the liquid against the 
object, then the object will sink. If the gravitational pull is less than 
the upwards push of the liquid, then the object will float. If the two 
forces are the same, then the object will just hang there, neither 
floating nor sinking.

Tbe ice cube floats not only because of its density, but because of its 
shape too. Imagine a huge ship. It's made of lots of heavy metal and 
steel, but it still can float. This is because of its shape. It is made to 
spread out wide over the water, so that there is more water that can push 
up from below to balance out the weight of the ship. If the ship were just 
a solid cube of metal, then it will sink, because the force of the water 
pushing from below, the bouyant force, is not enough to balance out the 
weight of the ship, and it sinks.

I hope this explanation helps, and if you have any more queries, feel free 
to ask us Mad Scientists!

Good luck! 
Tan "Clipper" Thiam Hock

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