Why does ice float on water? [ Detailed Explanation ]


Why does ice float on water? When a solid mass of a substance is put on a liquid of the same substance, it generally sinks. The atoms or molecules in a solid are usually closer together, than are the atoms or molecules in their liquids and gases. So, most solids are denser than their liquid and gas forms. But there are some exceptions. Some solids such as silicon, germanium, bismuth, and ice are less dense than their liquids. Therefore, these solids float on their liquids. But this is never seen in nature, except for water, because the melting points are too high. So, why does ice float on water? Because ice is less dense than water and less dense matter floats on more dense liquids. Now we have to answer two questions: the first Why is ice less dense than water? and the second one Why does less dense matter float on more dense matter? In order to answer the first of these we need to take a closer look at water’s structure. A water molecule consists of 2 hydrogen atoms and 1 oxygen atom. Also, water molecules are not linear but angular. The oxygen and hydrogen atoms share electrons, creating a pair of chemical bonds. But an oxygen atom is bigger than a hydrogen atom and has more protons in its nucleus. So, the oxygen atom pulls the shared electron toward itself with greater force. As a result of this, the negatively charged shared electrons are closer to the oxygen atom which gives the oxygen atom a partial negative charge and leaves the hydrogen atoms with partial positive charges. This uneven charge distribution means that water molecules interact with each other. This weak interaction is called a hydrogen bond. When the temperature is above 4C, hydrogen bonds are quickly broken. Because water molecules have kinetic energy, this means that the hydrogen bonds are not strong enough to hold the water molecules together. When the temperature drops below 4C, the water molecules slow down enough to allow the hydrogen bonds to bind each other together. So, the molecule’s structure is re-formed by the hydrogen bonds. Being angular, water molecules cause empty spaces to appear in the molecule’s structure so that the volume increases during freezing. Now we have the answer to our first question. Ice is less dense than water because hydrogen bonds causes empty spaces to appear during freezing so that the volume increases and the density decreases. Moving on to the second question why does less dense matter float on more dense matter? In order to answer this, we need to understand Archimedes’ principle. This states that when an object is completely or partially immersed in a fluid, the fluid applies an upward force called a buoyant force or buoyancy on the object. This force is equal to the weight of the fluid displaced by the object. So, we can calculate the buoyant force by measuring the weight of displaced fluid. Think about a fully immersed object. The buoyant force tries to lift the object to the surface, whereas gravity tries to pull the object to the bottom. If the buoyant force>the force of gravity, then the object will accelerate upward, rise to the surface, and then float on the surface partially submerged. If the buoyant force=the force of gravity, then the object will float fully immersed. If the buoyant force isdensity of object, buoyant force – gravity force will be positive, buoyant force >gravity force, so the object will accelerate upward, rise to the surface, and then float on the surface partially submerged. if density of fluid=density of object, buoyant force – gravity force will be zero buoyant force=gravity force, so the object will float fully immersed. if density of fluidgravity force, from which it follows that ice floats. So know we know why ice floats on water.

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22 thoughts on “Why does ice float on water? [ Detailed Explanation ]

  1. sir cold water more dense more heavy then hot water does it mean any body swim easy into cold water because cold water have more up thrust force

  2. Sir I have few question in my mind
    Q.No.1.which degree centigrade water is most suitable and easy to swim??
    Q.No.2. is water upthrust force help swimming and avoid drowning?
    Q.No.3 is it realy more dense water mean more easy to swim??
    Q.No.4 is hot water more density or cold water???

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