# Size does matter

There is a very interesting article by the biologist J.B.S Haldane on the sizes of various animals and how it affects the way they live , the things they have to care about etc . It is called ” On being the right size”.

Great article ! a must read !

Take the force of gravity . It is helluva important to large animals

like man . Take a guy to first floor and drop him . Will break his bones .

But take a fly to the 7th floor and drop her . Nothing happens to Miss Fly .

Now take the force of Surface Tension ( The force exerted by

the surface of liquids ) . We dont bother about it . We can go into a

swimming pool and come out with 1/15 inch of water on our body . But a

fly once wet may have to carry 2 times its own weight of water film .

It is in a very serious position indeed !! Die Fly !

Now consider the problem of flight . Principles of Aeronautics

say that a plane which has 4 times the linear dimentions of another

plane must fly 2 times as fast to keep airborne. That is why most birds

are of small sizes . Large size birds have to float . And even a limit

to the size that can soar is soon reached .

The eye can only be an efficient instrument if it is large . It must

have a lots of rods and cones to see anything properly . 2 objects can be

seperated only if their images fall on seperate rods/cones . Therefore

small animals have big eyes( compared to their bodies ) .

Small mammals cannot live in extreme cold . The surface area of

their bodies is large but they have small weights . They cant eat too much

but they need lots and lots of food to keep them warm ( many times their

body weight ) . The smallest mammal above the arctic circle is the fox !!

So friends look around u . If something is teeny weeny it may

have a good reason to be teeny weeny

# Social and antisocial particles

There are two kinds of particles : Bosons and Fermions .

Fermions have half integral spins . For example electrons are Fermions and they have +1/2 or -1/2 spin .

Bosons have integral spins . Photons are bosons and have spin of -1 , 0 or 1 .

Fermions are not very social creatures . No two Fermions can be in the

same state at a given time . They just dont wanna come close !! This was

first described by Pauli in his famous exclusion principle .

Bosons on the other hand are very social people . They love being together .

If there are n bosons in a particular state then all nearby bosons want to

come to that state too !! They wanna come close .

These bosons lose their identities and only the collection has an identity .

It is like a coir . All people have their distinct voices but u only

hear one voice . The voice of the group .

There are many phenomenon related to the “social” behaviour of bosons .

1. Photoelectric Bunching : If a photon strikes a surface and releases a

electron at time t then the next photon will strike immediately and

release another electron .

2. Superfluidity : At 2.2 degrees K helium loses all viscosity . It flows

without any friction . Viscosity is caused when one layer of a fluid

has resistance to the nearby layer . But Helium is a boson and

all the helium atoms wanna move together . They dont wanna resist

other helium atoms . They all move together and the liquid flows

without any viscosity !!!

# Napoleon goes to Russia

Today we will talk about Napoleon’s Invasion of Russia .

In June 1812 Napoleon took an army of half a million people and invaded Russia . This was the biggest army ever to invade a country .

Napoleon had planned that the invasion will last only a few weeks .

The Russians under Marshal Kutuzov knew that if they try and fight Napoleon in a direct confrontation they would be defeated in no time .

So they adopted a strategy of “strategic retreat” . This means that the russian army withdrew more and more into russia ( away from Napoleon) and destroyed all Russian land and villages as they retreated .

This meant that Napoleon did not get any supplies on the way ( no food , no shelter , no nothin ) . He had to rely on supply lines from France and supplies from that place took a long time . The army faced starvation . And by september the army had reduced to 2/3 of what it was initially .

On Sept 7 1812 the Russian and french armies met 70 miles from Moscow .

By the end of the day 108,000 people were killed . The Russians decided that they cant win so they decided to retreat further .

Moscow was evacuated . The Russian army retreated . While retreating the Russians destroyed Moscow to ensure that Napoleon does not find any supplies there . On Sept 14 Napoleon entered Moscow . There was nothing there .

There were fires all around and the cruel Russian winter was setting in .

The Army’s spirit broke . No place to live , no food and horribly cold .

Remember that Napoleon had begun his invasion in June and was not prepared for winter . That meant no winter clothes .

The army waited in Moscow for some time( mid Oct) for some sign of treaty from

the Russians and when there was none they decided to go back to france .

The retreat was equally horrible . The clothes on the soldiers tore

exposing them to bitter cold . No food . And on the way back the

army was constantly under attack from Russian Cossacks who killed

any stragglers .

By thye time the French came back they were reduced to 10,000 people .

The invasion was a big disaster .

This  was the beginning of the end of Napoleon’s great empire .