why does ice float on water physics

From giant icebergs to tiny cubes, ice the frozen form of water always floats on its liquid form. Isn t that weird? We re not the only ones who think it s unusual;Pthe entire world finds it rather surprising that a solid should float on its liquid form. Do a quick Google search and you ll findPdozens of pages discussing this queer tendency of ice. As it turns out, like everything else, there is a scientific reason behind this phenomenon. But first off, let s be clear about what makes stuff sink or float. The singular rule of thumb, when it comes to the ability of an object to float in water (or any other liquid), concernsPthe density of the object in question. Have you ever heard of Archimedes Principle? Archimedes Principle states that for an object to float on water, it must displace an equal amount of water. In other words, you can say that the fate of an object in a body of water is decided by Archimedes Principle. It s common knowledge that solid objects have more density than their liquid counterparts. Chemically, this makes sense too. Molecules are more closely bound with one another in a well-defined manner in a solid, which makes them rigid and gives themPmore weight. All common substances that we see and observe in daily life follow this basic principle: solid objects are denserPand have more weight than liquids.


Given that,Pwhy does ice which is a solid float on water? Shouldn t it sink,Pas a solid, and according to general convention, also have more density? Water is a wonderful liquid, and full of unusual behaviors and chemical structures, which is why itPpresents an interesting exception to the general behavior of solids floating over their liquid forms. If you keep cooling a liquid, its density continues toPincrease untilPit becomes solid, where it attains maximum density. However, in the case of water, this trend is slightly different, which is the root cause of this whole discussion. Water s density increases as you continue to cool it; but opposed to other liquids, which have their highest density when they freeze, water achieves maximum density when its temperature reaches 4 degrees Celsius (39. 2 Degrees Fahrenheit). If you continue to cool water past 4 degrees Celsius, its density starts to plummet (you can see this in the graph). At zero degrees, i. e. , the temperature at which water turns into ice, the density of waterPis actually quite low. It turns out that ice has a lower density than water, and any object that has a lower density than the liquid form on which it s kept (in this case, water) will be able to float!


But why is the density of ice less than water? To answer that, you ll have to look at the chemical structure of water. The negatively-charged oxygen atoms bind strongly with hydrogen atoms, forming a strong hydrogen bond. When a liquidPis cooled, more and more molecules are brought closer together and need toPbe accommodated in a smaller area. This gives mostPsolids more density than their liquid form. However, in the case of water, the negatively-charged oxygen atoms repel each other (when brought together in a smaller space) to prevent the ice from becoming any denser. This is the reason that density actually decreases as temperature continues to fall below 4 degrees Celsius.
The simple answer is that ice is less dense than water. The question then becomes: Why is ice, which is water in solid form, lighter than water in its liquid form? Something must be happening to water when it freezes. One molecule of water has two hydrogen atoms and one oxygen atom, or H2O. The hydrogen atom is slightly positive, and the oxygen atom is slightly negative.


At room temperature, these water molecules are loosely linked and free to move around easily, which is what defines the liquid state of matter. Once the temperature hits 32 F, or 0 C, the molecules line up in a rigid six-sided honeycomb structure, with water moleculesБthe more positively charged hydrogen attracting the more positively charged hydrogenБlinking up with each other in a process called hydrogen bonding. This causes the molecules to move more slowly and take up more space. You have ice. Because the same weight or mass now takes up more space, it is less dense and floats on water. We can put salt on ice to melt it. Salt is sodium chloride, or NaCl. (Technically, most salt for sidewalks is potassium chloride, or KCl, but the chemical process works the same way. ) The sodium atom in a salt molecule has a slight positive charge, and the chloride atom has a tiny negative charge. More On This. Ask a science teacher Why is snow white, and where does its color go when the snow melts A water molecule has one atom of oxygen bound to two atoms of hydrogen. The hydrogen atoms are БattachedБ to one side of the oxygen atom, resulting in a water molecule having a positive charge on the side where the hydrogen atoms are and a negative charge on the other side, where the oxygen atom is.


The sodium chloride ions pull and tug on the waterБs two hydrogen atoms (unlike charges attract) and tear the bonds apart. The ice no longer has a honeycomb structure. It has melted. In order for the melted ice to freeze again, it has to go much lower than 32 F; the salt has lowered the freezing point of the water. Most of EarthБs ice is packed into huge sheets called glaciers. The largest glacier covers most of the Antarctic continent and holds about 90 percent of the worldБs ice. If all of it were to melt, the oceans would rise 187 feet. You might want try this science experiment. Fill a drinking glass with water, and then put an ice cube in the water. You can see that the ice cube floats. Now, using isopropyl rubbing alcohol that you can buy in any drugstore, fill a glass with alcohol and carefully drop in an ice cube. What happens to the ice cube? Alcohol is less dense than water, less even, than frozen water, so, since the ice cube is denser than the alcohol in the glass, it sinks. From the book, ; Copyright , 2013. Publishes December 17; available wherever books are sold.

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