I weep over Newton's grave ...

[ChrisGreaves]

NASA probe enters orbit around asteroid
"But in space, where there is no counteracting gravitational force ..."

[HansV]

Simplified a bit too far...

[Don Wells]

Nice to know that you think while you read Chris.    

[John Gray]

It seems unlikely that they were thinking about a Lagrangian point...

Nor that the namers knew anything about the Thomas Weelkes' madrigal "As Vesta was from Latmos Hill descending". (I would have posted a link to a YouTube video, but the recordings are truly awful in all those I found.)

[stuckling1]

It seems unlikely that they were thinking about a Lagrangian point

My understanding of the Lagrangian point is that it requires the net gravitational force of two bodies.

From reading the ABC article, I think it would make more sense to say "no air resistance" , so no force to oppose the gas thrust. So the acceleration can be constant, albeit very small, and then the momentum can indeed build up over time

Physics is great!

[ChrisGreaves]

Simplified a bit too far...

OK, so here's the complete sentence
But in space, where there is no counteracting gravitational force, momentum builds up over time.

I object to a report in a news(paper) aimed at the general public that simplifies a statement to the extent of suggesting that there is any place in the universe, where there is no gravitational force. The Big Bang theory, Oscillating Universe Edition, depends on gravitational force reaching out to the farthest particles and bringing them back into the fold.

I agree with the post below that the science writer/editor probably wasn't thinking of LaGrange in writing this, the more so because the w/e is describing a body in motion rather than a body at rest with respect to an orbited body (which I think is what we have at a LaGrangian point⁽¹⁾)

Indeed the phrase "counteracting gravitational force" suggests a force (in this case the ion-drive) that acts counter to a gravitational force, which to my simple mind seems to suggest that there is, in deed, a gravitational force which needs to be acted against by the ion drive (I think I'm spiralling into a circular argument here).

I am also struggling, even with my fertile imagination, to see how else momentum can be built up if not over time, since a build-up of momentum implies either a change in velocity or in mass ("OK guys, they're the same thing ...") and a change in velocity is acceleration, which is, I thought, a rate of change of velocity, and a rate of something is measured over time.


But most of all I object to this pap being emitted under the banner of Reuters.
I can only guess that while I wasn't looking that brash Aussie bought out Reuters and just can't hack it.

⁽¹⁾ There's a good pop song in there somewhere, along the lines of "Home, Home at La Grange, ..."

P.S. I recommend "Marcus Chown of New Scientist Magazine on his Top 10 Bonkers Things About the Universe", which I've not viewed but have enjoyed listening to while walking these streets. (sample quote: "Today's sunlight is about thirty thousand years old")

[ChrisGreaves]

Nice to know that you think while you read Chris.    

Hi Don.
Is there any other way of reading?
Is there any better way of stimulating thinking than by reading

[ChrisGreaves]

It seems unlikely that they were thinking about a Lagrangian point...

I'd simplify this to read "It seems unlikely that they were thinking."

[ChrisGreaves]

"The motion, which is about equal to the pressure of a sheet of notebook paper on the palm of your hand, is so gentle it would be useless on Earth. But in space, where there is no counteracting gravitational force, momentum builds up over time."

... I think it would make more sense to say "no air resistance" , so no force to oppose the gas thrust. So the acceleration can be constant, albeit very small, and then the momentum can indeed build up over time

Almost anything would make more sense.
I suspect that, coupled with the preceding sentence, what they wanted to say was something along the lines of "Close to the earth, an ion drive's force is overwhelmed by earth's gravitational field, but away from such a massive body, the ion drive's power can have a significant effect".

Of course, I'm no science writer

Physics is great!

I agree!

P.S. Actually, now that I think about it, I'm not so sure that " ... it would be useless on Earth". There must be a great many experiments on earth where an ion drive, weak as it is, would serve as a very finely-tuned force on small amounts of matter.
The old charged-oil-drop experiment might be improved by being able to tap a small oil droplet with an ion drive.
if the ion drive is fueled by an electric current, a near-infinitely variable current would provide a great degree of variability of power from the ion drive, no?

[stuckling1]

There must be a great many experiments on earth where an ion drive, weak as it is, would serve as a very finely-tuned force on small amounts of matter.

Particle accelerators use electrostatic forces to create a beam of high-speed ions;
the mass spectrometer also uses a beam of ions, which are accelerated before being deflected to differing degrees by a maganetic feild.

The old charged-oil-drop experiment might be improved by being able to tap a small oil droplet with an ion drive.
if the ion drive is fueled by an electric current, a near-infinitely variable current would provide a great degree of variability of power from the ion drive, no?

charged-oil-drop experiments I've seen have been to demo the effects of electric- or magnetic- feilds on point charges - so a good demo of the ion-beam propeller would be to suspend an oil-drop in equilibrium in an electric or magnetic feild, before blasting it with a shot from the ion beam, at right angles to the inital feild. The curvature of the subsquent path of the particle would the depend on the feild - magnetic feild would give a circular curve, whereas electric would give a parabola.

Then lots of exciting equations, like F = mv/BQ and F = 1/4piE0 . Q1Q2 / r2 can be brought into the mix. Fun fun fun!

(just a spot of revision for my a-level physics exam that I did weeks ago! )

[ChrisGreaves]

Physics is great!

Not at The Toronto Star.
"Beating the Heat for $20"
The Star's Randy Risling ... demonstrates how to pump more heat energy into an already hot room by channeling electrical energy!

But please see also Fallacious Energy

[ChrisGreaves]

charged-oil-drop experiments I've seen ... (just a spot of revision for my a-level physics exam that I did weeks ago! )

Out with the Old, in with the New!

A simulation of a charged-oil-drop was the first real computer program i wrote, after working out how to calculate determinants of a square matrix!

[stuckling1]

how to calculate determinants of a square matrix!

So that would be revision for the Further Maths exam I did weeks ago then! :P

(Just out of geeky curiosity, did you use 2x2 matrices to simulate in 2dimensions or were you adventurous with 3 or even higher d matrices? And did you use a matrix to represent the transformation of the position of the drop, in which case the determinant would be the displacement? What did you write the simulation in? Matlab? Mathematica? Java? )

</barrageofquestions> I'm looking forward to being taught to program properly, when I've learnt how I might try tackling this myself.

[ChrisGreaves]

(Just out of geeky curiosity, did you use 2x2 matrices to simulate in 2dimensions or were you adventurous with 3 or even higher d matrices? And did you use a matrix to represent the transformation of the position of the drop, in which case the determinant would be the displacement? What did you write the simulation in? Matlab? Mathematica? Java? )

I started off with a brain-dead exercise. "Simulate a random walk", as in a coin-toss.
I had refused to write a program to calculate e-to-the-x on the grounds that I had a table of logs, tans, sines etc and it was pointless (as I thought at the time) to lug 2,000 punched cards around (The FORTRAN II compiler!) when I could just carry this slim book in one of my geeky shirt pockets.

The random-walk took me only a few days to write.
FORTRAN II on an IBM 1620, 80-column cards in, and out. No printed output; no printing on the cards. Hold the little blighters up to the lights and read the Hollerith codes.
I just added dimensions, so in the end I think I had nine vector arrays, each representing a variable in the oil-drop's environment.
3 for spatial, one for mass, one for charge, three for orientation, ... forget the rest.

I thought I was quite brave, at the time.
All of this done between 2am-6am, the only time I could get to use the computer.

Sigh.

The Good old days.

The determinants were a separate exercise, and are the cause for my ending up on Eileen's Lounge and spreading so much gloom, alarum and despondency across the planet.
I used to calculate determinants by hand, late at night, and I'd do each calculation twice, getting two separate results (probably Heisenberg's fault, but I didn't know that at the time), so then I'd do "best out of three", and on weekends "best out of five".

Then I learned that one could write a program ONCE and run it as often as one wanted, and it always gave the same result.

I remember one night I ran my little determinant program 20 times, and lined up all 20 output decks to check that light, glorious light, shone out of each tiny chad-hole.

THAT is what got me hooked on computers - get rid of all the boring and repetitive work.
From there it was a small step to a position as trainee programmer at AIS, then ICL, then WARCC, then the UK, Paris, Singapore, and finally Toronto where I met my canoing buddy, Fred, who, lent me a copy of The Underground Guide to Windows", and hence Woody's Lounge and ... here I am.

It's all Heisenberg's fault, I'm ceratin of that.
Or there again, maybe I'm certain of that.

[Becks]

While it obvious that there is an "escape velocity" for leaving the Earth's gravitation field, there is also an escape velocity for leaving the solar system (I'm too lazy to calculate either). I suspect an ion engine would not provide sufficient thrust (a force in opposition to a gravitational field) to escape if starting from rest.

From memory, Voyager 1 used the the gravitational fields of Jupiter and Saturn in order to attain sufficient velocity to "escape" (It should escape the heliopause sometime in next couple of years, but will not truly escape for a very long time ~16,000 years to reach outer extent of Oort cloud )

From there it was a small step to a position as trainee programmer at AIS, then ICL, then WARCC, then

I probably submitted programs to the WARCC while you were there...

Kevin

[ChrisGreaves]

I probably submitted programs to the WARCC while you were there...

Really?
On the 1620 they ran the water and electricity board stuff, as I recall.
Since it was a government-funded installation (my details are sketchy; i had no real idea), I think the deal was that both the government and the Uni shared the device in blocks of time.
ICL-SDC and the SA government had the same sort of arrangement at S.A.I.T in the early 70s.

What programs did you submit, and were they to the IBM 1620 or to the DEC PDP-6?

[Becks]

It was probably the PDP-6. Much too long ago to remember. Jobs were submitted for my Applied Maths unit (I think) I still have my copy of "Numerical Methods & Fortran Programming" by McCracken & Dorn
When I started doing Honours, the Chemistry Department installed a teletyper so I no longer had to submit the boxes of cards (joy of joys!)

Kevin