Problem Solving Strategies

3:40 AM

@Malavika What's the problem? I'll try to help if I can :-)

@Malavika yeah I'll try to help...don't worry...JR Sir is also there :-)

@Malavika Well...don't worry...we're there... :-) All of us can make it better....Don't be so upset :-)

@Malavika okay, do you use Google chrome :-)

@Malavika I agree...Internet can teach you a lot of things....I'd say the best thing I found on the web is well....this SE chatroom :-)

@Malavika Are you confused between momentum and KE

@Malavika FB is not that great...Even I don't...However...Whatsapp is more private and safe :-)

@Malavika and are you browsing on Google Chrome?

@Malavika okay so often we'll need to write mathematical equations...so install this app

@Malavika chrome.google.com/webstore/detail/se-chat-mathjax/…

@Malavika okay now this will help us to write fractions and other math equations ;-)

@Malavika we're there ;-) Don't worry

@Malavika Momentum shows us how difficult it is to stop something

yuvraj singh

4:09 AM

15

Q: Difference between momentum and kinetic energy

From a mathematical point of view it seems to be clear what's the difference between momentum and $mv$ and kinetic energy $\frac{1}{2} m v^2$. Now my problem is the following: Suppose you want to explain someone without mentioning the formulas what's momentum and what's kinetic energy. How to do ...

Hi morning to all:)

user8718165

@Malavika hii

@Malavika Good Morning :)

@Malavika yeah I had... What 'bout you?

@Malavika Have it quickly :-)

@Malavika which language are you trying to learn?

@Malavika Kinetic energy tells us how much energy has been given (stored) in that object to get it moving with some velocity $v$

@Malavika It can be shown (you may be knowing it) that $$K.E\propto p^2$$

user8718165

4:47 AM

@Malavika That's a scripting language used for web dev. Do you know HTML and CSS

@Malavika Great :-)

@Malavika All the best:-)

@Malavika Did you now understand KE and momentum?

user8718165

5:16 AM

@Malavika yeah I used to watch it previously....That's very good for basics

yuvraj singh

8:13 AM

@JohnRennie morning , party hangover. Lol

John Rennie

@yuvrajsingh we didn't drink very much, but I was out late and I'm tired now :-)

yuvraj singh

I mean that only, sir I know you don't, t drink much, it is about fun and then tiredness.

John Rennie

@yuvrajsingh yes :-)

yuvraj singh

I was awake whole night, @JohnRennie

John Rennie

@yuvrajsingh Partying? Or are you having difficulty sleeping?

John Rennie

8:36 AM

@Malavika hi :-)

user8718165

@Malavika please ask JR Sir.... I don't know the reason why it's constant :)

@Malavika hello Malavika :)

Hello @JohnRennie sir :-)

John Rennie

All conservation laws are related to symmetries. The name for this is Noether's theorem, though to understand this requires more maths than you have unless you go on to do a physics degree.

Noether's theorem

Noether's theorem states that every differentiable symmetry of the action of a physical system has a corresponding conservation law. The theorem was proven by mathematician Emmy Noether in 1915 and published in 1918, after a special case was proven by E. Cosserat and F. Cosserat in 1909. The action of a physical system is the integral over time of a Lagrangian function (which may or may not be an integral over space of a Lagrangian density function), from which the system's behavior can be determined by the principle of least action. This theorem only applies to continuous and smooth symmetries...

So conservation of momentum happens because there is a fundamental symmetry of the universe that is related to it.

user8718165

@Malavika How difficult it is to stop a given moving object.... That's it I think....:-)

@JohnRennie does that make sense Sir?

I've to leave for a 4 hr class soon :-(

John Rennie

And that symmetry is basically that the laws of physics are the same everywhere in the universe. That is, if I do an experiment in one place in the universe I will get the same result as if I do it in another place in the universe.

The symmetry is called translational symmetry:

Translational symmetry

In geometry, to translate a geometric figure is to move it from one place to another without rotating it. A translation "slides" a thing by a: Ta(p) = p + a. In physics and mathematics, continuous translational symmetry is the invariance of a system of equations under any translation. Discrete translational symmetry is invariant under discrete translation. Analogously an operator A on functions is said to be translationally invariant with respect to a translation operator T δ {\displaystyle T_{\delta...

@Malavika what is it about light that you're asking?

Are you asking how light can have momentum when it has no mass?

@Malavika I'm just answering a question on NMR in another room. I shouldn't be too long.

164

Q: If photons have no mass, how can they have momentum?

As an explanation of why a large gravitational field (such as a black hole) can bend light, I have heard that light has momentum. This is given as a solution to the problem of only massive objects being affected by gravity. However, momentum is the product of mass and velocity, so, by this defini...

special-relativity electromagnetic-radiation photons mass momentum

yuvraj singh

9:05 AM

Sir I think I discussed with you somewhere we see, that momentum is not always conserved. @JohnRennie

John Rennie

@yuvrajsingh momentum is always conserved if no external force is acting.

yuvraj singh

Let me search.

Aah I got it.

It's because you are assuming that the wall is fixed and cannot move.
So you have an external force keeping the wall in place.
That external force acts where the wall is attached to the Earth i.e. at the base of the wall.
In principle when you bounce a ball off the Earth both the ball and the Earth move after the collision, and this conserves the momentum. But in practice the Earth is so much heavier than the ball that we consider it fixed.
The price we pay for this is that with this assumption momentum is no longer conserved.

@JohnRennie

John Rennie

Yes

yuvraj singh

Sir do you remember I discussed with about inertia I discuss with my professor can you confirm what he actually mean please sir @JohnRennie

John Rennie

@yuvrajsingh my problem with this is that inertia is such a vaguely defined word.

yuvraj singh

9:17 AM

I understand but, this is the question I asked him.

how would you define inertia in space where, I assume body experience no force.

This what he said :) If you see the definition of a nertia it fits space :with no forces acting it will keep at rest in this inertial frame or move with constant velocity. Forces are defined to show the difference between inertial frames., to have a model to calculate when there is acceleration, i.e. change in velocity.

@JohnRennie

John Rennie

If you have a body floating alone in space then there's no way to measure its mass, because you need some form of interaction with it to get its mass.

But just because you can't measure its mass doesn't mean the mass is undefined.

yuvraj singh

Do you satisfied with answer. @JohnRennie

John Rennie

@yuvrajsingh yes. What he is saying is that the way to measure the mass is to apply a force to the object and measure its acceleration.

Newton's second law tells us $F = ma$, so if we apply a force $F$ and measure an acceleration $a$ the mass is $m = F/a$.

yuvraj singh

Ok

John Rennie

9:32 AM

@Malavika yes, and in fact that is basically how mass is measured.

You apply a know force and see how much the object moves.

Light objects move a lot while heavy objects don't move much.

Just to be confusing there are two types of mass. We have been talking about inertial mass. That's the type of mass that affects how much objects move when we push them.

There is also gravitational mass, which is determines how heavy an object is when it's in a gravitational field like Earth's gravity.

Though it's a fundamental principle in physics that these two masses are actually the same thing, just measured in different ways.

Suppose you and some mass are floating space. You can apply a force to the mass by pushing it. Then you and the mass will both move away from your oriignal position.

@Malavika yes

So you could measure the gravitational force between the two masses and use that that to calculate the product m1m2.

:-)

user8718165

10:17 AM

@Malavika hello :-) actually it's a break during class so I'm here :-)

@JohnRennie hello sir @JohnRennie

@JohnRennie are you working now Sir?

@Malavika yeah..... :-)

@Malavika yeah I go sometimes :) what about you?

@JohnRennie :( :(

@Malavika see you later ;)

yuvraj singh

10:53 AM

@JohnRennie hi can you come in this chat room.

A General Chat Room

This is a general discussion room. Here we chat about random ...

yuvraj singh

12:15 PM

Yes,

Stage is set,.

Aman

any good books for problem solving strategies

yuvraj singh

In which subject, what kind of course.

Hello.

Here market and house full of lightening

user8718165

1:53 PM

@30772 you changed your name ? :-)

yuvraj singh

3:04 PM

I will upload photos day after tomorrow but I have a pic which I clicked yesterday, while i was coming from chandpole, it is a pic of Albert Hall. Lightening is so good but the camera is not so hope you understand

@user8718165 @JohnRennie @malavika i.stack.imgur.com/Wtjt0.jpg

You won, t believe when I show you pic of johri bazar what a decoration with a theme of Chandrayaan

I have but is in my cam,