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# Macrostates and microstates

In physics, a microstate is defined as the arrangement of each molecule in the system at a single instant. A macrostate is defined by the macroscopic properties of the system, such as temperature, pressure, volume, etc. For each macrostate, there are many microstates which result in the same macrostate.  Created by Sal Khan.

## Want to join the conversation?

• At , sal said at the Micro state is changing gazillion of a second but at last few minutes sal said "Micro state never changes , I don't get it , please tell me if I am missing something .
• He means microstate is defined every instant, not that it doesn't change. On the other hand, we cannot talk about macrostate in every instant since it's not well defined.
• At , why does the piston oscillates when the rock's mass is halved?

Thanks. :)
• If you're asking why it goes through a bit of harmonic motion (oscillation), it's because the top has momentum after it is pushed up by the pressure of the gas so that when gravity takes over it is a little above the level that it reaches equilibrium. Then gravity brings it down and gives it momentum so that it is a little below the equilibrium level and the gas pressure takes over again. This process of oscillation continues until damping allows the piston to reach equilibrium.
• At about , in discussing microstates, Sal says that we can know the position and the momentum. I thought that, because of the uncertainty principle, we can never know both the position and the momentum of any given particle. Is he just simplifying things so that we understand the difference between microstates and macrostates, or am I missing something?
Thanks.
• According to the Heisenberg Uncertainty Principle, you cant know both the location and momentum of a particle so you are correct. I believe it is a simplification.
• what sal had told at , an ideal gas is always single atomic molecule gas?
• An ideal gas is modelled as a monatomic gas.
• why do we express temperature in Kelvin?,why not in degree celsius?
• Temperatures like Celsius have an arbitrary placement of 0. 0 degrees C was decided to be the freezing point of pure water and 100 is the boiling point of water at standard pressure. The Kelvin scale has 0 set to be the lowest possible temperature. Since temperature is basically the average random kinetic energy by placing the base of the scale at 0 then you have a direct relation between this random kinetic energy and temperature.
• The product of the pressure and volume is equal to the product of the pressure and volume in the second case, right ? Thanks ! :)
• NO:). Its a constant as long as the temperature is constant. But in this case its doing some work (against the rock though its in space and i dont know how it affects the system). That implies that it's going lose some energy beacuse there's nothing else that is going to help the gas. This in turn means that the temperature of the gas drops. If the temperature drops, then the product of pressure and the volume becomes something else. I hope I've been coherent:)
• When Sal says he's using rho for momentum at , he means p, right? I'm pretty sure the momentum formula uses p rather than rho.
• The Greek alphabet and the English alphabet have similarities and differences.
Some examples:
If you look at a written or printed version of the Greek alphabet, you will see that the Greek letter "rho" looks just like the English letter "p." The only way to tell which you have is from context.
We don't have any difficulty recognizing the Greek letter "pi" because no English letter looks like it.
An upper case "Alpha" looks just like a capital "A," but a lower case "alpha" does not look like a lower case "a."
Hope this helps.
• I'm confused as to when the equilibrium took place, was it after the rock's weight was split in half? At that moment, did all the molecules shoot upward? That too and what is ideal gas?

I'm a 7th grader working for SciOly and these parts are rather confusing. I would appreciate any help. :)
• CRUX of the video :
1. macrostates : are the parameters which helps you quantitatively measure the properties of matter. you dont need to know much about atoms while measuring.

2. microstates : are parameters which helps in qualitative study of the properties of the material(gas) inside the cylinder which are in this case atoms / molecules.

3 Equilibrium : it is a state when everything settles means the macrostate & microstate properties do not change at different point of time.

4. the rock put on the pistin was halved . before, it was in equilibrium means pressure exerted by gas was constant . but when rock was halved the force exerted by rock also halved but pressure was contant in the gas so that means the force exerted by pressure of gas will dominate the rock force and move the pistin up. It is same as TUG of WAR game

5.ideal gas is a gas which will show behavior(macrostates) as predicted theoretically . in that case no friction air resistance an other external forces are considered. but it fails on earth to show the predicted values so on earth its called real gases.