Wednesday, 7 January 2015

ANOMALOUS BEHAVIOUR OF WATER

ANOMALOUS BEHAVIOUR OF WATER


We have discussed in previous post about causes of hydraulic system overheating and cost of hydraulic oil leaks as well as we have also studied various "Reasons of hydraulic hose failure". 
Today we will see why water is denser than ice?

Water is denser than ice

First of all we should understand that why water is denser than ice
As we know that liquid water has higher density at 40C temperature and decreases in density as it freezes.

The water molecules in ice are held in a rigid, six-sided geometric pattern by their hydrogen bonds, this produces an open, porous structure.

The molecules in liquid water are more loosely bonded. A greater number of liquid water molecules than ice molecules can occupy a given volume or we may say that there are more molecules per unit volume in liquid water than in solid ice. Therefore, liquid water is denser than ice.

Some points that we have to know before going for Demonstration

  1. As water changes into ice, it takes up more space than it does as liquid water, which is to say, ice is less dense than water.
  2. Ice floats. Ice is about 91% as dense as liquid water. This means that about 91% of floating ice is underwater and about 9% of the ice is above the water line.
  3. If we consider the transformation of  a certain amount of water to ice we can aware that no. of molecules will be same in liquid state and in ice state. But the space or volume covered by these molecules will be higher in case of ice state as compared to liquid state, and we know that, density = Mass/Volume so liquid state of water will be denser as compared to ice.

Also read: Sequence valve and pressure reducing valve

Demonstration

Let us take a glass container and fill it with water by ¾ of its total volume.
And mark the level of water
Put a block of ice in container

What we will observe?

  1. By observing ice closely, we can measure the displacement of the ice: 91% of ice is submerged; 9% emerges above the water line. Ice is 91% as dense as water.
  1. Water has a weight density of 62 pounds per cubic foot. A Cubic foot of ice displaces a cubic foot of water. A cubic foot of ice is only 91% of Weight density of a cubic foot of water, i.e. About 56 pounds, So 56 pounds of ice displaces 62 pounds of water. The 62 pounds of water pushes back with a resultant up thrust that floats the ice so that the difference in the two weight densities is up out of the water, 9%, or about 6 pounds.
  1. If an object displaces more than its weight in water, it will float. If an object displaces less than its weight in water, it will sink.

Principle and forces involved Archimedes' principle

When an object is immersed in a fluid, the up thrust on the object is equal to the weight of the fluid displaced.
  1. Archimedes' principle applies to all objects immersed in liquid regardless of whether they are floating or not
  2. The Law of flotation, however, only applies to floating objects
Archimedes’ principle describes buoyancy, or up thrust, the upward direction of fluid
Pressure .A body immersed in water experiences an upward force equal to the mass of
The fluid displaced by the body.

If the weight of an object is greater than the weight of displaced fluid, it will float. If the two are equal, it is suspended, neither floating nor sinking.

For example, when an object is placed in water, it will displace its own volume
Of water, and that water will push back against it proportionally, producing an up thrust.

 

Forces

1.    Buoyant force
The behaviour of an object submerged in a fluid is governed by Archimedes' Principle. Archimedes determined that a body which is completely or partially submerged in a fluid experiences an upward force called the Buoyant Force, B, which is equal in magnitude to the weight of the fluid displaced by the object.
The buoyant force is due to the difference between the pressure at the bottom of the object pushing up on it, and the pressure at the top pushing down. Thus:
B = (PB - PT) A

2.    Weight of the object – weight of floating object
In floatation, the buoyant force equals the weight of the floating object
The buoyant force is due to the difference between the pressure at the bottom of the object pushing up on it, and the pressure at the top pushing down. Thus:

B = (PB - PT)A

Also discuss

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