Floating icebergs

That water covers three quarters of the planet's surface and that all living beings are made up of a very high percentage of water, has been said many times. The first statement is easy to believe for anyone who has traveled by boat or has discovered the immensity of the ocean from an airplane; To believe the second, on the other hand, we need a good dose of faith in science because it is not something obvious.

Water occurs, in its natural state, not only in a liquid form but also in a solid (ice) and gaseous (water vapour) form. To study the differences between these different states of water we propose a couple of experiments.

Take a tray that is commonly used in the freezer to make ice cubes.

Fill the different receptacles to different levels and mark them with a permanent marker. Leave one nearly empty, one half full, and one filled to the top edge.
Put it in the fridge freezer and wait until it freezes.

What do you notice about the level of ice in each container?



From this experience, what would you say?:

  •  That the same mass of water occupies a higher / lower volume in the liquid state than in the solid state.

  •  That, therefore, the density of ice is higher / lower than that of liquid water.

  • That the water molecules are closer to each other / further away in the liquid state than in the solid state.

Now try to remember some phenomena related to frozen water that can be explained from what you have just observed. Think, for example, of icebergs,

Why do you think they float despite their great mass?



Surely you have ever seen a frozen lake in winter; Why do you think that only its surface freezes? What advantages does this have for life in rivers and seas?



Why in places where winter is very cold, where it usually freezes, do people have the foresight to empty or insulate the water pipes?




Now take a clear plastic bottle and fill it with water.

Add a few drops of food coloring and shake it so that the mixture is homogeneous.

Cover the bottle and put it in the fridge for a few hours.

Fill the bathtub at home with hot water. One third is enough.

Take the bottle out of the fridge and place it in the bottom of the bathtub.

Take the cap off the bottle and see what happens.

How does cold water behave? Does it mix with the hot? Does it rise to the surface or stay at the bottom?



Based on this experience, what would you say?

  • That cold water is more dense / less dense than hot water.

Once your experience is over, try to remember some phenomena related to water in a liquid state that can be explained based on what you have just observed. Think, for example, of ocean currents.

How do you think the movements of the great ocean currents that circulate from the poles towards the equator can be explained from the difference in densities between warm and cold water?



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