I am not here to talk on any high funda physics, I won't be discussing any hi-fi physics phenomenon, I am here to ask about some simple phenomena and effects that are associated with our day to day life. So now the question is,why have I chosen such simple topics. The reason is, now-a-days everyone is interested or keen to know about black holes,expanding universe and other complex phenomena. Everyone thinks that this is the biggest unsolved mysteries. But in doing this, we are shifting our focus from our day to day life science and the physics behind them. There are many such effects in our day to day life which are still unsolved and mysterious.
Now to start with, I want to ask a question. If I take two cups and take warm water say 70 degree Celsius in one cup and cold water say 30 degree Celsius in another cup and we put both of them together in refrigerator and let them to freeze. So what do you think, which one will freeze earlier? I think the obvious answer will be the cold water. If we see logically, the cold water takes 'x' minutes to freeze, then the water in 70 degree Celsius will take some time to reach 30 degree Celsius and then take 'x' minutes to freeze.So the warm water must take longer time.
But experimentally it is not so. The warm water takes lesser time to freeze as compared to the cold water. This unique phenomenon is used by many ice-cream makers to freeze their ice-creams quickly. This special effect is known as Mpemba Effect. Now the most important question is,what is the reason behind this phenomenon. Till now none of the scientists could come up with the perfect reason or there is no agreed upon explanation for how this phenomenon occurs. Various reasons might be involved for this phenomenon as-
(ii) Dissolved gases
So such a simple phenomenon, much simpler than black holes, expanding universe, but still no answer behind this phenomenon.
Now, moving on, I hope everyone has eaten cornflakes and cereals, so have ever noticed why cereals tends to clump together or cling to the sides of a bowl of milk ??? This simple phenomenon is known as Cheerios Effect i.e. the tendency for small wettable floating objects to attract one another. This phenomenon can be explained using three simple concepts of physics -
(i) Buoyancy- It determines whether an object submerged in water or surrounded by air will sink,float or stay out. If an object is less dense than the water or air surrounding it, the object floats, if the object is dense, it sinks.
(ii) Surface Tension- It is a property that makes the surface of a liquid like a flexible membrane. It results from various weak forces acting between liquid molecules.
(iii) Meniscus Effect- At the interface between water and air, water molecules at the surface are pulled forcefully by water molecules beneath them but experience only a weak outward pull from the air molecules above.Therefore the surface of the water caves in slightly forming a curve known as a meniscus. Depending upon the properties of the liquid, whether it is attracted to or repelled by the glass, the meniscus either curves upward(concave) or downward(convex).
So now what happens is that when we place a single Cheerio or cornflakes in a bowl of milk and its weight will cause the milk beneath it to dip slightly, forming a dent in the once-smooth surface of the milk. A second Cheerio placed into the bowl will form its own dent on the surface of milk, and if the two Cheerios drift close enough to each other, they will appear to 'fall into' one another, as if pulled together by an attractive force.Cheerios near the edge of the bowl float upwards along the curve of the meniscus to look like they are clinging the edge of the bowl. I guess nobody would have thought that there is also physics involved in our breakfast !!! But yeah... thats the magic of physics, physics is present everywhere...
So now again moving on, have you ever noticed that if we shake a bowl full of nuts along with Brazil nuts, the Brazil nut always pops out on to ??? Brazil nuts are like the big nuts,so if we see in terms of gravity, then as they are big, the have larger mass so they should have fallen down,but why they pop out on top??? Thus this phenomenon of the largest particle being on the surface of a granular material containing a mixture of variously sized objects is known as Brazil Nut Effect.
The reason behind this is Convection- The movement of small particles in large groups is called convection. When the container is subjected to vertical vibrations, the particles tend to get forced upwards from the center of the container. As they travel upwards, they leave empty spaces, and particles from the side slide inwards. They,in turn, leave empty spaces, which particles above and to the sides of them slide in to fit.
Since particles from the center are always pushing upwards, once they reach the top and can't climb higher, they tumble to the sides. Since the particles on the sides of the sides of the container are falling down to fill the space left by the upward moving particles in the center, once the particle tumble to the side, they get down to the bottom of the container again.But this does not happen for the bigger of them. The biggest of them stay on top. They stay on top because they can't fall back down.Smaller particles can slip down the small holes left by other small particles heading downwards. Studies have shown that density does have a role in the Brazil Nut Effect. If the large particles are much less dense or much denser than their surrounding particles,they rise to the top and stay. But those that have a small difference in density from the other particles tend to remain mixed. And all this density dependence stops if the particles are in a vacuum.Daniel Hong of Lehigh University in US researched on this topic and found out that condensation is also a reason behind this phenomenon. He found that it is the ratio of the masses and diameters of the sets of the particles that is crucial.If a sphere A is twice the mass and diameter of sphere B, the larger particle float. But if they are six times heavier and twice the diameter, they sink- an effect known as Reverse Brazil Nut Effect.
So if we can bring our focus back to these day to day activities we will find them very interesting. So in the urge of knowing the mysteries of the space,we must not loose focus from the simple physics related to our daily activities.