Gravitational Intensity on Thin Spherical Shell: Is it Ethical?

[neelakash]

Our instructor showed us in class that by applying brute force it is possible to give a value to the gravitational intensity on the surface of a thin spherical shell.

My question is whether it is ethical to do this.After all,the limits at r=R should not exist because,inside the sphere it is 0 and outside the sphere it has got a finite value.Therefore the LHL and RHL do not match.Please confirm.

 

[Danger]

How could it not be ethical?
Ethics only pertains to science if one is falsifying results or stealing someone else's work.

 

[Creator]

Our instructor showed us in class that by applying brute force it is possible to give a value to the gravitational intensity on the surface of a thin spherical shell.

.

Excatly, what did he do to demonstrate?; please be more explicit.

 

[Mentz114]

Do you mean 'correct' rather than 'ethical' ? Ethics is more about morality.

 

[neelakash]

Mentz114,Oh!
That's a wrong choice of word=>please bear with my poor English...It would be "correct" instead "ethical".

He was not demonstrating anything special.One of our friends asked him why it was getting infinite at the surface.He then told that using a limiting process it can be made finite.And showed that.

If you want me to show that,I will have to refer to the copy...I cannot remember more than that it was a limit e--->0 on an integration where the limits involved e.
e=> epsilon

 

[Mentz114]

Neelakash, glad to be of help with the subtleties of English.
Limiting processes are used sometimes in physics, but I'm not a mathematician so I couldn't pronounce on the validity of such procedures.

When Planck was working out the black-body spectrum, he originally intended to take a limit as the quantity h->0, then found it only works if it is a non-zero constant.

 

[neelakash]

You tell me one thing.

When you plotting E against r,
It is 0 at r<R
It is finite at r>R
How can LH limit equal RH limit?

 

[cesiumfrog]

neelakash, this might not be relevant to your specific question, but "at the end of the day" in physics it does not matter whether the techniques we use can be proven mathematically correct, just whether they lead to correct predictions in experiments. (Consequently, physics can sometimes be said to drive advancement in mathematics.)

Ethics only pertains to science if one is falsifying results or stealing someone else's work.

Incorrect. (It's important to acknowledge the incompleteness of that list.)

 

[Chris Hillman]

I am guessing that the idea was this:

1. Examine a spherically symmetric gravitational field consisting of three regions: interior vacuum $0 < r < r1$ with constant potential, solid spherical shell $r1 < r < r2$ with potential increasing in magnitude, exterior vacuum $r2 < r < \infty$ with potential decreasing in magnitude. Find the potential for given mass density in the shell and match to find the interior and exterior vacuum potentials.

2. Try to take a limit in which $r1 \rightarrow r2$, replacing of course the mass density (kg/m^3) with a surface density (kg/m^2).

So the question probably is: is this procedure mathematically legitimate? If not, does it give a physically reasonable result and if so, how can this be?

I'll let you guys mull these!

 

[Danger]

Incorrect. (It's important to acknowledge the incompleteness of that list.)

I'm not denying it, but I don't know what the rest of it might be. Those are the only things that I can think of. Maybe it's a matter of semantics. I can think of a lot of nasty things, such as the Holocaust medical experiments, but I don't consider them a matter of ethics as specifically related to the science itself.

 

[cesiumfrog]

We'd like to think of science as "pure", but scientific research invariably affects other living things.

- If teaching physics, you can not deliberately vary your style and publish statistical results without approval of the university ethics committee.

- As an applied physict, one should consider the implications of doing work for (say) the Department of Defense (versus perhaps a renewable energy company).

- Obviously 'most every experiment needs ethics approval in medical and biological sciences. Similarly the risks (eg. to the populace) from unforeseen outcomes should be assessed in high-energy physics experiments.

- Even publishing theoretical work can have implications for other people. Is it a good idea for (say) a social scientist to begin a data analysis project that is expected specifically to demonstrate a correlation between race and intelligence?