Category: physica

A note on triple and critical points

The Pressure – Temperature of a pure substance is commonly plotted as follows:


When you take a look at such a graph, there are two points on it that are particularly fascinating. (rest are all boundaries) : The Triple and Critical point.

Most people might be familiar with a triple point. This is where the solid liquid
and gaseous phase are in equilibrium.


 In the above animation, Gas phase is at the Top half of the container, Liquid at the bottom and Solid phase is sandwiched between the two phases.

If one keeps moving past the triple point and along the liquid vapor boundary line on the P-T diagram, one would notice that this boundary line terminates at a distinct temperature and pressure !!!

This point is known as a Critical point.


Beyond this point distinct liquid and gas phases do not exist and the substance is known as a super-critical fluid.

In order to understand what that really means, watch the following didactic demonstration of a super-critical fluid transition: (It is absolutely beautiful)

One of the reasons why the critical point is crucial is that close of the critical point, small changes in pressure or temperature result in large changes in density. And industries love to take advantage of this to fine tune their processing methods.**

Have a good one!

* We have discussed the phase diagrams for only pure substances here. But phase diagrams for mixtures are interesting too. Check this out.

** Decaffeinating coffee + Video demonstration of decaffeinating using Supercritical CO2  

What can science tell us about history repeating itself?

Poincaré Recurrence theorem

The Poincaré recurrence theorem states that certain finite systems
will, after a sufficiently long but finite time, return to a state very
close to the initial state.

The  Poincaré recurrence time tells you how long one should wait for the recurrence to occur.


Now if we churn out the numbers for the universe, the Poincaré recurrence time comes out too be this special number:


If we abstract ourselves from the possibility of experimentally testing it out, the key takeaway from this is that the Poincaré recurrence time is a finite number and one does not need to wait forever to observe the recurrence of events in the universe.

Therefore in Physics it does not make any physical sense to talk beyond this time scale.

Great question! Thanks for asking!

May 11,2018  – Richard Feynman’s 100th BirthdayRemembering a…

May 11,2018  – Richard Feynman’s 100th Birthday

Remembering a man whose passion for understanding the laws of nature was seeded in every milestone of his life- Richard.P.Feynman. 

Though it has been more than 30 years since he has passed away, the
legacy that he left as  both a brilliant physicist and a masterful
storyteller and teacher continues to live on forever.

* Feynman playing the bongos

Introducing FYP’s book club

We are starting a new segment on the blog where we recommend one or two books in Math or Physics that everyone can read.

And this month it is : A Mathematician’s Apology by G.H.Hardy which is available for free to download here and here


You are absolutely welcome to share your comments and reviews here once you are done. Also, if you would like us to check a book out, do let us know too!

Have a good one!

fuckyeahphysica: Diamagnetic Levitation -Ig Nobel prize…


Diamagnetic Levitation -Ig Nobel prize (2000)

In the previous post we took a look at how combinatorics and paramagnetism gel together. In today’s post we will talk about levitating frogs and diamagnetism.


                                         Diamagnetic material

A diamagnetic material is one which would rather ‘die’ than be attracted to a magnetic field (it opposes the magnetic field).

Paramagnetic materials on the other hand are those which love to align themselves paralled to the magnetic field.

The opposition of this magnetic field sets up a restoring force that pushes it away from the field. For example take a look at this diamagnetic tomato which is being a baby about a strong magnetic field and keeps moving away.


                                       PC: University of Hull

Why does the frog levitate?

Frogs and most living creatures on earth contain high concentrations of water and water is a weakly diamagnetic material.

Here is the diamagnetic levitation of a tomato which, as you know is flush with water:


                      Gif source credit:  Radboud Universigy

In order to accomplish this a very large electric current is made to pass through a ‘bitter electromagnet’.

This generates a high magnetic field around the frog. The frog being diamagnetic opposes this field generating a opposing force.


             PC: mriquestions

Now since the frog is light in weight, the diamagnetic force generated is sufficient to overcome the effects of gravity enabling the frog to levitate.

Can Humans be levitated like this ?


Well, for levitating a frog that weighed around 25 gms one had to use a 15 Tesla coil. A typical MRI machine uses only a 3 Tesla coil and this took 5 times that.

The magnetic fields required to levitate a human is too crazy to be achieved at the moment but as research in superconductors advances maybe we will be able to get to a high enough magnetic field to at the least test it out.

Have a great day!


From levitating frogs to a nobel prize

Much more detailed explanation on the levitating frog

** BONUS: A follower of this blog pointed us to this video by The Action Lab who performed this crazy demonstration using a large Neodymium Magnet and a mouse.


It should be of no surprise to you that this works since most living creatures on earth contain high concentrations of water and water is a weakly diamagnetic material.

Have a great day!

This week on FYP! – Earth’s rotation

ICYMI we have been talking about Earth’s rotation for the past week on FYP!

We started off by asking the simple question: ‘Why did the Earth start spinning in the first place?


And how has this rotation been affected by the moon over the course of centuries.


But this did not give us any understanding for why the axis of rotation is inclined  by 23.5 degrees.

This is where we were introduced to the The Giant Impact Hypothesis which suggested that the Moon formed out of the debris left over from a collision between Earth and an astronomical body the size of Mars, approximately 4.5 billion years ago


Now one of the consequences of living on a rotating object is that it flattens at its poles. The name given to such a flattened object is an oblate spheroid. We understood this using a simple experimental setup:


Leaving all that aside, it was strongly believed by people for a really long time that it were the heavens that moved and not the earth.

It took a lot of debate among philosophers to come to the conclusion that it was indeed the Earth that was rotating. We looked at one such remarkable argument given by Galileo


Having made this journey so far, we finally discussed how humans found a way to utilize the fact that we are on a rotating oblate spheroid to quench our thirst for the ecstatic understanding of the unknown.


Earth’s rotation is slowing slightly with time

Earth’s rotation is slowing slightly with time:

“In the year 1820, a rotation took exactly 24 hours, or 86,400
standard seconds. Since 1820, the mean solar day has increased by about
2.5 milliseconds.”

“At the time of the dinosaurs, Earth completed one rotation in
about 23 hours,” says MacMillan, who is a member of the VLBI team at
NASA Goddard.

* How can the moon slow down the earth ?


Are the heavens moving or are we?


In the previous series of posts, we discussed about the key role that a rotating earth plays in space shuttle launches and quickly skimmed through why the earth began to rotate in the first place.

But in the 21st century, there are many experiments  (Coriolis effect,  Foucault’s pendulum ,etc, etc) that you can do to convince yourself that the Earth is indeed rotating.


                                             ISS Live Stream

But back in the days of Galileo it was still debatable whether Earth was rotating or not. 

Why does a ball thrown straight up in the air fall to the same place on the ground ?


of the profound Aristotelian arguments against the rotation of the
Earth was that if the Earth were rotating, a thrown ball/arrow would not
land in the same place that it was thrown.


This was believed so
because, by the time the projectile traverses its path the Earth would
have moved by a certain distance. Hence, the ball would never land at
the same place it was thrown.


Take a second to think about this. Can you come up with an argument against this rationale ?


is an excellent argument given by Galileo in favor of the rotation of
the Earth and why things would still fall to the same place even if the
Earth were rotating:

In replying to this, those who make the earth movable answer that the canon and the ball which are on the earth share its motion or rather that all of them together have the same motion naturally.

Therefore the ball does not start from rest at all but to its motion about the center joins one of projection upward which neither removes not impedes the former.

will see the same thing by making the experiment on a ship with a ball
thrown perpendicularly upward from a catapult. It will return to the
same place whether the ship is moving or standing still

The profundity of this argument is that, the very same principle that ‘ball does not start from rest at all  but with velocity of the earth’ is used by space shuttles to reach orbital velocity with lesser fuel consumption.


But despite Galileo’s argument, it was still believed for a long time that it were the heavens that moved and not the earth.

God hath established the world which shall not be moved in spite of
contrary reasons because they are clearly not conclusive persuasions.


fuckyeahphysica: The Tale of Earth and it’s sister Theia. Have…


The Tale of Earth and it’s sister Theia.

Have you found it weird that the earth’s axis is tilted by 23.5 degrees and wondered what led to this? Wait, Where did the moon come from?

Well, Here’s what scientists have theorized.

The Giant Impact Hypothesis

Theia, a mars sized planet collided ( it glanced and thankfully did not collide head on, else it would have destroyed earth ) with the Earth around 4.553 billion years ago.


Theia’s debris gathered together around Earth to form what we now call- The Moon.


The collision between the early earth and Theia was so immense that
it tilted the axis of rotation of the early earth by 23.5 degrees.

it remains tilted so that way even today!!


Why do they believe in this hypothesis ?

Scientists have a very good reason to believe in the Giant Impact Hypothesis:

  • Earth’s spin and the Moon’s orbit have similar orientations.
  • Moon samples indicate that the Moon once had a molten surface.
  • The Moon has a relatively small iron core.
  • The Moon has a lower density than Earth.
  • Evidence exists of similar collisions in other star systems (that result in debris disks).
  • Giant collisions are consistent with the leading theories of the formation of the solar system.
  • The stable-isotope ratios of lunar and terrestrial rock are identical, implying a common origin

Have a good day !

PC: sarice,

Now not only do we now have an understanding of why the earth is spinning but also why the axis of rotation is inclined by 23.5 degrees.

Stay tuned for more..

Why did the Earth start spinning?

We have been discussing about the rotation of the Earth in the past couple of posts but lets take a second to understand why the earth is rotating in the first place.

Here is a quick summary:

Our Solar System formed about 4.6 billion years ago when a huge cloud
of gas and dust started to collapse under its own gravity.


As the cloud collapsed, it started to spin. Some of the material
within this cloud gathered into swirling eddies and eventually formed
into planets. As the planets formed, they kept this spinning motion.


As material gathered in more closely to form a planet, like Earth, the
material spun faster. This is similar to what you see when skaters pull in their arms and spin

And as a result since there are no forces are acting on Earth to slow it down, it continues to spin to this day. **

** not entirely true as we shall explore soon

Previous posts:

The shape of the Earth is an oblate spheroid: A visual demo

How does earth’s rotation affect space shuttle launches ?