Great to hear!

:)

Yes.....

Legend only birth once.

Hey genia where are you studying in

Thanks 👍

That's what I also thought

en.wikipedia.org/wiki/Equipartition_theorem

No such video exists.

lectures 32 and 33 are the Thermodynamics section. Think you should of asked was "What textbook did you use and chapters I can investigate these topics in?"

The first qn can be interpreted from ideal gas law itself. V is proportional to T. Since temperature is so small, volume of gas inside the balloon is decreased. The volume approaches 0 at -273°C.

correct

8.01 Physics Hans C. Ohanian 2nd edition W.W. Norton & Company ISBN 0-393-95748-9

What do "homogeneity" and "isotropy" mean? (Intermediate) Can you please give me the definitions of homogeneity and isotropy in astronomy terms?This is a good question, because these concepts are a bit subtle. Homogeneous is defined as "the same in all locations" while isotropic means "the same in all directions." Imagine that the whole universe is an infinitely large field with one perfectly symmetrical hill, which you are seated atop. Look around: you see an isotropic universe, since the hill is equally green and equally steep in all directions. But the universe is not homogeneous: it has a hill!These concepts are important because most modern cosmology is based on the "cosmological principle," the assumption that, on large scales, the universe is both homogeneous and isotropic. Studies of large-scale structure in the universe and analysis of the microwave background radiation help confirm that this assumption is justified. Homogeneity is the sameness of things. If you're looking for homogeneityin your wardrobe, you'll want shirts and jeans that all have something similar about them.Homogeneity can also mean that something is the same throughout. Plain yogurt has a homogeneity about it - it's white all the way through and it should be the same texture throughout. On the other hand, yogurt with fruit at the bottom can be described as having heterogeneity - different textures and different colors. The Greek root homo-, means "same," and genoa means "race" or "kind" - so homogeneity is the quality of being "the same kind. i·so·tro·pic (ī′sə-trō′pĭk, -trŏp′ĭk) adj.Identical in all directions; invariant with respect to direction."cosmic microwave background Cosmic microwave background (CMB): Isotropy in the cosmic background Apart from the small fluctuations discussed above (one part in 100,000), the observed cosmic microwave background radiation exhibits a high degree of isotropy, a zeroth order fact that presents both satisfaction and difficulty for a comprehensive theory. On the one hand, it provides a strong justification for the assumption of homogeneity and isotropy that is common to most cosmological models....

2 protons + 2 neutrons in a helium nucleus have a lower mass than 2 single protons and 2 single neutrons due to "binding energy".

you are welcome

do what you like

>>>>If temperature remains constant indepent of the height>>>> it doesn't - use google

Mountain tops are generally colder than surrounding land at sea level because air masses use (in part) their internal thermal energy to "climb" to higher elevations. As a result of trading internal thermal energy for gravitational potential energy, the air mass decreases in temperature. The air expands and does work on its surrounding air. As a result, its surroundings do work on it, to lift it to higher elevations. This isn't the only weather factor that comes in to play, as it would predict a temperature as cold as 180 Kelvin for the top of Mt Everest, which would freeze you solid. Heat transfer with the surrounding land heated by sunlight, will also come in to play

Yes. The air in the balls should be what makes it bouncy.

you measure other variables, then calculate the constant

Castor Gemini Yes that is correct, oxygen becomes liquid at 90 K, the liquid nitrogen that I used was 70 K.

Lectures by Walter Lewin. They will make you ♥ Physics. Thank you, Professor!

Lectures by Walter Lewin. They will make you ♥ Physics. Can you upload your edX videos? I remember you saying some really insightful things like "Faraday's law powers 1/3rd of the global economy" and I can't find them anymore. Can you also upload the other edX materials (e.g. problem sets) somewhere?

+Lectures by Walter Lewin. They will make you ♥ Physics. Sir, Could it be also because air in the balloon is at an elevated pressure, and increasing the pressure will raise the boiling point temperature at which the gas can liquify and since air is a mixture hence its liquification occurs at higher temp than Pure N2 ?

How many minutes into the lecture?

As you can see from the phase diagram, at room temperature CO2 starts to become liquid when the pressure is around 60 atm and the pressure stays at 60 atm until all gas is turned into liquid. 300 atm was calculated if CO2 is assumed to stay entirely in gas phase. According to the phase diagram, at 300 atm, CO2 is in liquid phase and ideal gas law does not apply.

I watched at 11:03. I do explain the v^2 cearly; I cannot add to the clarity of my lecture. I suggest you watch it again and LISTEN also to what I said.

@Sarvesh Padav It's the momentum transfer per second that is proportional to v^2, not just the momentum transfer. The explanation is clear on the textbook (Ohanian Physics 2nd edition). The momentum transfer per second is momentum transfer divided by a time interval or simply 2*m*v / t where t is the time needed by a molecule to travel a distance L if it had the average speed v. We know that speed equals distance divided by time or simply v = L / t and solving for time t we gain t = L / v. Now replace that time t into 2*m*v / t and you will see that momentum transfer per second is equal to 2*m*v / (L / v) = 2*m*v^2 / L from which is obvious that momentum transfer per second is proportional to m*v^2 and thus to v^2.

You are welcome!

en.wikipedia.org/wiki/Bernoulli%27s_principle

physics.info/gas-laws/summary.shtml

I did not cover that in 8.01. use google

that is not lit. i guess. it is m cube. 1 lit. = 10e-3 m cube

nope

@@lecturesbywalterlewin.they9259 Please do make lectures on them sir

He actually did it

@@aakashchakraborty3673 where are those lectures can you pls tell

momentum is a vector. It changes from +mv to - mv.

sir i get 2mv...part but mv^2 part i dont get. While multiplying the extra "v",you said it is the no. of particles colliding with wall per second. I did not get this part !!!

Yes that's what I said and I also mention Why I multiply by v.

Actually I didn't get it either in the 1st place , how did the extra "v" came into multiplication but here is my little calculation . Think about a box of length L . assuming each of molecules has an average velocity of v , the molecules starting from the one end of the box and colliding on the other end , it will take them a roundtripping time of 2L/v, so they bounce off the wall v/2L times per sec, each time delivering momentum 2mv, so the wall will pick up momentum from this “gas” at a rate of 2mv multiplied by v/2L per second. So the force from the gas on wall: F = rate of change of momentum =mv^2 /L. An equal opposite force must be supplied from outside to keep the wall at rest.

2mv= total change in momentum F momentum per second F=2mv/t t=distance covered by molecules /average speed of a molecule t =l/v F=2mv×v/l×1/6n 1/6n is the no of molecules moving in one direction F=(1/3l)mv^2 P=F/A P=(1/3V)mv^2

Most welcome

+snipez285 N moles of helium have a mass of 4N grams. That's independent of the pressure.

No.of moles remain constant. Volume changes in such a way that PV/T remains constant, considering the gas to be ideal

I suppose that when you start pressing the gas at 60 atm the gas starts to become liquid and to occupy less space, and finally you get CO2 liquid with 1/5 of the original volume and at 60 atm, so you can put 5 times more liquid than gas if both at 60 atm with 20°C. No sure if that's right.

YES

Thanks Professor.

+Family Father Energy is conserved. If you stretch a spring, over a distance x, the work I have done is 0.5k*x^2. k is the spring constant. We call this potential energy (PE) of the spring. If now I release the spring, this PE is released in the form of kinetic energy (energy is conserved). This picture is adequate to see why atoms when heated store PE (think of them as being springs). The original heat energy is released when the atoms go back to their ground states. The PE becomes zero again.

+Lectures by Walter Lewin. They will make you ♥ Physics. Thank you for the response, but is the cooling of a substance that allow atoms to oscillate near the equilibrium point (Like a SHO when there is low mechanical energy on the system) or is the formation of bonds that take heat of the system? In high school and in basic chemistry material on the web it looks like it's implied that the forming of bonds liberate heat, but it makes more sense to me (while I don't know if that's correct and would appreciate to know for sure) that the refrigeration of a gas is what makes the atoms loose kinetic energy and that allows the forces to be stronger, since it would be oscillating near the lowest potential point and, because of the asymmetry of the PE curve (in relation to the distance in which the forces are zero), the molecules/atoms would be more close to each other, resulting in a liquid or solid. When a magnet is let go next to a metal, the PE goes to kinetic that goes to heat when it collapses with the metal, but I think that the heat generated can be explained in a molecular level as the chaotic movement of the metal molecules, caused by the collision, that increases the average kinetic energy of the total metal molecules (temperature). I've never heard a explanation to really why is heat generated when a bond is created, and how it corresponds to a chaotic motion of molecules that spreads to the outside of the system. I may be a little bit confused with the molecular interpretation of heat and also of PE when dealing with gases (It's due to the electromagnetic forces that act between the molecules/atoms, isn't it?), so I don't know if I was able to clearly put out my doubts, but anyway thank you for your answer, and for all your brilliant and inspiring lectures available for everyone and inspiring a lot of people to love physics!

+Family Father Energy is conserved. If you heat matter you put in energy. Thus if you cool it you get that energy back. If you change ice into water you have to add energy. Thus if water becomes ice, energy is released. There are nice demos to show this. Take an undercooled liquid. Thus its temperature is bellow its "freezing" point. Shake it some and all the liquid becomes solid and you can feel with your hand that its now every warm. Energy is released.

question uncler

Sir when you did an experiment with balloons by dipping them in liquid nitrogen the volume of the balloon contracted more than what was calculated. Is that because of pressure exerted by liquid nitrogen the balloon.

yes liquid!

search online - maybe MIT's OCW

ask google

Avogadro’s number, number of units in one mole of any substance (defined as its molecular weight in grams), equal to 6.022140857 × 1023. tell me how C12 was used?

​@@lecturesbywalterlewin.they9259 Carbon-12, the most abundant and stable isotope of Carbon, is the reference isotope for how the amu and mole are defined (or were defined when I first learned it in the early 2000's). Its atom is by defnition is 12 amu in mass, which would mean a "charcoal briquette" of exactly Avogadro's number of pure C12 would be 12 grams. At one point, Oxygen-16 and Hydrogen-1 were both used in a similar manner. Carbon's most common isotope produced experimental results that allowed for a compromise between these two standards.

At STP (standard pressure and temperature: aka - 0 degrees C and 1 atm) one mole is 22.4 L - at RTP (room temperature) it is 24 L

In talking and during lectures I always say "X degrees Celcius" and "Y degrees Farentheit" and "Z degrees Kelvin". Just Lik I also say N centimeters an M kilograms. What you write is a different matter and it depends on your taste.

@Lectures by Walter Lewin. They will make you ♥ Physics. yes sir..But doesn't that mean the mass of the substance taken will matter ?

mass does matter. READ MY previous msg

it's on a playlist in my channel

I hear no sound so I cannot answer.

@@lecturesbywalterlewin.they9259 sir but you only have asked the question in the end of lecture about the reason for sound of gas from container.

@@lecturesbywalterlewin.they9259 sir he is asking about the questions which you gave to think about at the end of lecture.

I do not know - I suggest you check google - pressure vs temp.

use google

Simrandeep Bahal molecules/atoms always collide in "perfectly elastic" way, because there is no non-conservative force involve during collision. only conservative force (electrostatic force) is involved during molecular collisions.

search try MIT OCW or EdX or Coursera

@@lecturesbywalterlewin.they9259 we can't find Your lectures, is what we' re asking. Btw I bought the book(your book), which you recommended me the other day, i just got it yesterday from Amazon, it seems amazing.

@@shatakshisharma5240 which book

yes the theory is applicable to O2 and N2. Those are as ideal as they come

+Jordi GS Temperature of outer space is 3K (black body radiation). A Nobel Prize was awarded for this discovery.. I suggest you google "microwave background radiation".

I like the way you ask the question . Thanks a lot professor , really you are great.

use google

@@lecturesbywalterlewin.they9259 I found no clear answers in that Professor

I will try to explain using the ideal gas law. We know that P, V, N, and T are the parameters that describe an ideal gas. From the experiments, we find that P and V are inversely proportional when N and T are kept constant, V and T are directly proportional when P and N are kept constant, etc. So one can say (PV)/(NT) always gives you the same number (for example k: Boltzmann constant) as long as you use the same units (for example: SI units) in your calculations. And that number is not always equal to 1. So constants are needed to make the equations numerically correct as well as the units consistent. It is like the following. We know that area area of a circle is proportional to the square of its radius but numerically area is not just equal to radius^2. You need a constant to make it numerically correct. And as you know, that constant is pi. I hope this helps.

This law is derived from gas laws and R=PV/nT =8.3 J/K, you can search the derivation on google, you will found the derivation from gas laws

Think about a box filled with N gas molecules with random velocities. Find the pressure on the walls by considering the frequency of collisions with the sides and the resulting momentum transfer to the sides. The only other thing you need to know is that the kinetic energy for a monoatomic gas is E= 3/2 kT =1/2 m v_rms ^2, with v_rms the root mean square velocity of the gas. This is very straightforward to carry out and requires nothing more than 8.01 level mechanics.

Adiabatic = no heat transfer Isochoric = fixed density, usually constant volume processes as it would be in a closed system Isothermal = constant temperature Isobaric = constant pressure Adiabatic on its own isn't enough to specify the process. The P*V^k = constant relation for adiabatic processes, where k is the specific heat ratio cp/cv, only applies to adiabatic/reversible processes. Also known as adiabatic/isentropic. Think a piston moving slow enough in the cylinder, without friction, that the pressure can equilize at every point along the way. I.e. much slower than the speed of sound in the gas. Joule-Thompson processes are also adiabatic, but they aren't reversible.

pdf file below the video thumbnail

@@lecturesbywalterlewin.they9259 Exactly sir, there is no diagram in the PDF file.....

do not be lazy - use google

how many minutes into the lecture?

Lectures by Walter Lewin. They will make you ♥ Physics. Sir at 10:50

momentum transfer is mv if the particle is absorbed; it's 2 mv if the particle reflects. the higher the speed the less time it takes for the transfer. Thus the momentum transfer per sec (in both cases) is proportional to v^2.

+Roy Velazquez on the web

Thanks!

google Avogadro's number.

*By lowering the pressure on the water you can make water boil at temperatures of only 1-2 degrees Celsius (it's a classic demo in lectures) , but you cannot boil an egg in that water as that boiling water is freezing cold!*

Lectures by Walter Lewin. They will make you ♥ Physics. Ok sir i got it now thank you very much

@@dhaval326 It depends on how you are cooking. If you are frying an egg directly on the skillet surface, elevation will not matter nearly as much (if it does at all). If you are depending on boiling water or steam to transfer heat to your food, elevation will matter a lot. If you can only get your boiling water to 80C, it will not cook nearly as fast as it would at 100C. Take a look at product recipes that give high altitude instructions, and notice that what they have in common is dependence on boiling water. Oatmeal, pasta, rice, etc. Compare this to products with recipes that don't involve boiling water, and you will notice this modification isn't included. An example being pre-made dough for home baked pizza crust.

Dank je! :)

If you place a cup of hot water and one of cold water (same amount of water) in your freezer. the hot water will freeze faster. The reason is that hot water has a much higher vapor pressure than cold water thus the hot water will evaporate much faster than the cold water. For every gram water that evaporates 540 cal are needed and that makes the temperature of the hot water go down much faster than that of the cold water. Thus, by the time that the hot water is as cold as the cold water, there is LESS water in the original "hot cup" than there is cold cup. That's why the hot water wins the race. Convection plays no role.

how many minutes into the lecture?

imagine a airplane. airplane goes with velocity V. particles hit airplane surfaces with velocity V but number of molecules hit the airplane propotional with V. then aerodinamic force propotional with V square.

@@miko_52niko6 why is this force proportional to v in case of water then?

I cannot give you any advice as I do not know you. Talk to your teachers.

You can clear your doubt just mail me I am a chemistry faculty

correct

PLEASE learn how to use google

Mass no =no of Proton +no of neutron While atomic mass is mass of 1 mole of substance

Mass number is a "nameplate" mass of the isotope in question. It counts the nucleons (i.e. protons and neutrons) in the nucleus. It doesn't care whether these particles are exactly 1 amu or not. It is always an integer. Atomic mass of an isotope accounts for other nuclear factors that come in to play. Not every nucleon is exactly 1 amu, and not every proton/electron pair is exactly 1 amu either. They are on average in Carbon-12 by definition, but other nuclear factors affect the overall mass as the nucleons form the atom's nucleus. Atomic mass of an element, accounts for the mix of this element's isotopes at their relative abundance percentages as they are found naturally on Earth. Both the isotope atomic mass and the percent abundance are multiplied for each isotope in question, and then added up to get a sum total.

@@purushottamgupta3155 The mole and the gram are not relevant to the definition of atomic mass. That is molar mass. Atomic mass is at the scale of the individual atom. The mole is set up by definition, so that molar mass is the same number as atomic/molecular mass, except in units of grams per mole, instead of amu/(atom or molecule).

:)

took me 10 sec to find the answer in google

what is P?

I meant 'Pressure'....sir

Pressure exerted is equal from all directions so it's net force & acceleration should be 0. So g might not depend on P

But, the magnitude of Pressure does depend on 'g'. Since, those planets are nothing but ball of gas, the very matter which makes them are compressible and thus makes 'g' vary, unlike on rocky planets such as earth. Again, pressure is responsible for the non-uniform distribution of mass. That's why I stated that.

​@@schattopadhyay1901 Those planets aren't exclusively gas phase. It is just that the gaseous layer of the planet is significantly thicker in proportion to the diameter at the visible edge than it is for any terrestrial planet or moon in the solar system. They all have solid rock cores, and a solid outer core. Jupiter in particular has metallic hydrogen in its core. Indeed it is true that the higher value of g on Jupiter makes the atmosphere's pressure and density gradients a lot higher than that of Earth's atmosphere. Gravity is responsible for the variation in atmospheric pressure, and subsequently the non-uniform distribution of the atmospheric mass.

Well, critical temperature of water is 374°C... You should read the definition of critical point.

Critical temperature is the highest temperature upto which a gas can be liquified by increasing pressure. It does not mean that the gas cannot exists in liquid form below that temperature.

Great!

It's probably a matter of habit. Calling all units of temperature a degree in some form or another.

+Prakash Kamath Look again, the water is boiling.

Density of wall=ρ=M/{Volume of wall} So, ρ=M/{XA}, where A= "total wall area". Now momentum transfer is: ∆p/T=←(2m/MX)mV². =←(2m/ρX²A)mV². Net force from wall is due to the sum of all the particles that hitting cross sections, each of value "δA": Σ∆p/T=←(A/δA)(2m/ρX²A)mV² =←(2m/ρX²δA)mV² Assume particle diameter D is of the order of D~|dX|=|dx| and it's speed is: dx/T=V=½(M/m)v. So, as v=X/½T: dx/T=V=½(M/m)(X/½T) =(M/m)(X/T) So, D~(M/m)X X~mD/M Net force is now: Σ∆p/T= ←(2m/ρX²δA)mV² ~←(2m/ρ(mD/M)²δA)mV² =←(2XA/MD²δA)M²V² =←(2XA/D²δA)MV² Pressure on wall is ←Net Force / ←Area: P~←(2XA/D²δA)MV²/←A =(2X/D²δA)MV²

Number of particles hitting wall=N: N=A/δA So, Pressure on wall is P~(2NX/D²A)MV²

D~10⁻¹⁰{m}. 1/D²~10²⁰ {m⁻²} Number of degrees of freedom is 3, so 2N becomes 6N inside the gas, so there is factor ~6N*10²⁰ {m⁻²} in the formula: P~(6N*10²⁰{m⁻²} )(X/A)MV² XM~mD, so this is also: P~(6N*10²⁰{metres⁻²} )(D/A)mV² A=NδA: P~(6*10²⁰{metres⁻²} )(D/δA)mV² δA~¼πD²: P~(6*4/π)*10²⁰{metres⁻²} )(mV²/D) ~7.639*10²⁰{metres⁻²} (mV²/D) ~7.639*10³⁰{metres⁻³} mV²

22.7 Liters/mole is the value at 0C and 1 bar pressure. 22.4 Liters/mole is the value at 0C and 1 atm pressure. His example uses 293 K (i.e. 20 C) and 1 atm pressure. IUPAC changed the definition in 1982 to use the bar ("the metric atmosphere") instead of the atmosphere as the definition of "standard temperature and pressure".

@@carultch *Thank you carultch for your many very thoughtful and very useful comments. Keep it up!* As a thank you note I'd like to send you a signed copy of my book "For the Love of Physics" if you don't have one yet.

Bhavnao ko samjho

ok shut up

When we compress an ideal gas, we can do so in a variety of ways. If we do the compression very slowly so that the gas is always in thermal equilibrium with its environment, then the temperature stays constant and the compression is isothermal.www.physicspages.com/2015/07/09/isothermal-and-adiabatic-compression-of-an-ideal-gas/

Thank you very much for your reply.. However, my question was about real gases, it wasn't about an ideal gas..

real gasses are a pain in the neck

use google

It was found to be 300 assuming the co2 remained a gas. That's why he could apply the gas law. But as it went liquid after 60 atm, the gas law was not working with a gas now, so it gave the wrong answer.