if photons in motion have mass and energy why don't they knockstuff over

In article ,
Bjoern Feuerbacher wrote:

4B wrote:
What about those small propels that "mysteriously" spin when they are put
close to a source of light. Is not the momentum of the photons that make
them spin?

1) Don't top-post, please.
2) *Lots* of photons are acting there together.
3) You need an apparat with very few friction forces for this to work.
4) It is constructed especially to maximize the effect, by making one
side black and the opposite one light-reflecting.

Bye,
Bjoern



Indeed!

And if the radiometer (the small propeller thingie) has a vacuum inside
the glass bulb, the propeller spins in one direction, but, if the there
is air inside, it spins in the other direction.

--
Rudy Garcia

"jonathan" wrote in message
...

wrote in message
news:4074AA39.32669.141C70C@localhost...

like little things like blades of grass or ants out of a tree

I see from the responses that everyone ...completely... missed
the most important point.

In sci.physics, regardless of the OP's expectations, the point
is always physics, and there's plenty of that in this thread.
Jonathan is requested to peddle his cracked pottery elsewhere.

[Old Man]

[snip diarrhea]

Jonathan

"jonathan" wrote in message
...

"Old Man" wrote in message
...

"jonathan" wrote in message
...

wrote in message
news:4074AA39.32669.141C70C@localhost...

like little things like blades of grass or ants out of a tree

I see from the responses that everyone ...completely... missed
the most important point.

In sci.physics, regardless of the OP's expectations, the point
is always physics, and there's plenty of that in this thread.
Jonathan is requested to peddle his cracked pottery elsewhere.

[Old Man]

[snip diarrhea]


"The aim of science is not things themselves, as the dogmatists
in their simplicity imagine, but the relations among things; outside
these relations there is no reality knowable."

Henri Poincaré, Science and Hypothesis, 1905


I am talking on-topic. You simply can't recognize that fact
since you're so out of date. Tell me, what's it like living at
the turn of the nineteenth century?

Jonathan

Jonathan

At the time of writing, Poincaré probably knew little about
relativistic invariance. He is forgiven. Jonathan isn't. Even
Newton knew that acceleration and rotation rate weren't
relative. Both are absolute and self-referential. Overcast
skys that hide the "fixed stars" aren't an obstacle to their
measurement. Local, self-referential, measurements are
guarantied to reveal Mother Nature. Global concoctions
are the fairy tales of metaphysics. The local speed of light
is absolute. E(dot)B and E^2 - B^2 are local relativistic
invarients. For electromagnetic plane waves, they are both
absolutely zero, no matter the observer's relative velocity.
[Old Man]

Well, that's a common misconception: actually, photons are knocking things over
all the time.

Richard Schumacher wrote:

Well, that's a common misconception: actually, photons are knocking things over
all the time.

The rhodopsin molecules in the cones take quite a beating.

Bob Kolker

"Old Man" wrote in message ...
"The aim of science is not things themselves, as the dogmatists
in their simplicity imagine, but the relations among things; outside
these relations there is no reality knowable."

Henri Poincaré, Science and Hypothesis, 1905


I am talking on-topic. You simply can't recognize that fact
since you're so out of date. Tell me, what's it like living at
the turn of the nineteenth century?

Jonathan

Jonathan

At the time of writing, Poincaré probably knew little about
relativistic invariance. He is forgiven. Jonathan isn't. Even
Newton knew that acceleration and rotation rate weren't
relative. Both are absolute and self-referential. Overcast
skys that hide the "fixed stars" aren't an obstacle to their
measurement. Local, self-referential, measurements are
guarantied to reveal Mother Nature. Global concoctions
are the fairy tales of metaphysics. The local speed of light
is absolute. E(dot)B and E^2 - B^2 are local relativistic
invarients. For electromagnetic plane waves, they are both
absolutely zero, no matter the observer's relative velocity.
[Old Man]

This is when you think that a photon is "electromagnetic plane waves"...

However, when you realise that we describe the photon - the two
collision system which self-regenerate itself - by their projections
into electrical and magnetic properties - indeed you will realize
that they do knock stuff over...

The Poincaré quote repeats the Lucretius and Newton understanding
of 'first beginnings' and of 'substance'... I call the same no-things
elementary units of existence. There is nothing knowable about them,
but only about their collision events, 'relations' (blows for Lucretius,
'constituting space and time' for Newton, for me, the self-regenerating
collision sytems are the 'relations', knowable).

Cheers!
Aladar
http://stolmarphysics.com

wrote:

if photons in motion have mass and energy why don't they knock stuff
over like little things like blades of grass or ants out of a tree

They do. A recent ( last year? ) NOVA had a segment about a guy
in New Mexico who blasted aluminum disks about 20 meters straight
up using a laser DOE had left over from fusion research. He could
keep them up as long as the laser was on and the disk was in the
laser beam.

Because of the inefficencies of the process it takes a lot more
than a few mW laser to do this.

Also simple glass-bulb radiometers demonstrate photon momentum.

tom

--
We have discovered a therapy ( NOT a cure )
for the common cold. Play tuba for an hour.

In article , (Tom Kirke) writes:
wrote:

if photons in motion have mass and energy why don't they knock stuff
over like little things like blades of grass or ants out of a tree

They do. A recent ( last year? ) NOVA had a segment about a guy
in New Mexico who blasted aluminum disks about 20 meters straight
up using a laser DOE had left over from fusion research. He could
keep them up as long as the laser was on and the disk was in the
laser beam.

If he was doing that in air, he wasn't using photon pressure.

Assume photon pressure is responsible.

Assume a 1kg aluminum disk. That's 1 kg * 9.8 m/sec of momentum
per second. Divide by 2 because that aluminum better be a damned
good reflector. E = pc. So you have 1 kg * 9.8 m/sec / 2 * 3 * 10^8
meters /sec ~= 7*10^8 joules every second = 700 megawatts of light power
hitting an aluminum disk massing 1 kg.

Assume 99.99 reflectivity. That's 70 kilowatts of heating power.
Divide by 4.2 to get calories/sec, multiply by 10 because the
specific heat of aluminum must be pathetic, divide by 1000 because
it's one kilogram and you have around 150 degrees Celsius per
second temperature rise, back-of-the-envelope.

Note that disk mass factors out of the result. The bigger the
disk, the bigger the mass, the more power you need and dividing
out the thermal mass leaves you back where you started.

Poof goes the aluminum disk, inside of ten seconds.

I imagine you could pull the trick off by ablating aluminum. That'd
cut your power requirements quite a bit and take care of the cooling
concerns at the same time.

Because of the inefficencies of the process it takes a lot more
than a few mW laser to do this.

Also simple glass-bulb radiometers demonstrate photon momentum.

Actually, they demonstrate the opposite. They demonstrate that
whatever photon pressure there might be is inadequate to offset
the temperature and pressure effects induced by those same photons.
They spin the wrong way.

John Briggs

"jonathan" wrote in message
...

wrote in message
news:4074AA39.32669.141C70C@localhost...

like little things like blades of grass or ants out of a tree


I see from the responses that everyone ...completely... missed
the most important point.


They talk of forces and equations, fields and quantities. Yet
a single pedestrian aspect of photons, such as one
striking the eye and causing it to move, effects almost
every moment of all our days.

What is important is not what things are, their weight, size
or speed, but what they ....do. What their effects and
relationships are to other things. It is the connections
between things that matter most, not what they ...are.

Behavior matters most.

We must unlearn our backwards methods of objective reductionism and
embrace subjectivity and holism. We must strive to expand our
scales of observation first, while turning subjective judgments
into a science.

We must embrace the future and dispense with the Dark Age
mentality that still infects every corner of this world and even
this ng.



Jonathan


Indeed, the real philosophy we should strive toward is the 'nothingness of
all'. In it, all aspects of the universe are one-ness, and each element of
the universe is but a projection of all other elements into that particular
space of nothing-ness and relative nothing-ness.

Let me tutor you a little bit on Buddhist philosophical thought.

Existence then is a function of the fourfold states of matter's "existance",
JO-JU-E-KU, JO (pronounced "Joe") being birth and increase, JU (pronounced
"Joo") being stability, E (prounouced "eh") being decrease and KU
(pronounced "Koo") being nothingness or the rest state.

Every "thing" in the corporeal universe then is merely a transcient
projection of KU (nothingness) which in fact is actually the realm of "true
potential existance" possessing all aspects of everything, and since is KU
is nothingness, it is everywhere "things" are not. It is all potential.
Read a little bit about the probability event wave and quantum universes.
Then you 'might' understand why photons don't poke your eye out as
effectively as a RedRyder BB rifle will.

And so, I guess your little philosophical point is then lost in the face of
Nothingness, since all points are made when nothing is said. Get the point?

O'

"jonathan" wrote in message
...

"Old Man" wrote in message
...

"jonathan" wrote in message
...

wrote in message
news:4074AA39.32669.141C70C@localhost...

like little things like blades of grass or ants out of a tree

I see from the responses that everyone ...completely... missed
the most important point.

In sci.physics, regardless of the OP's expectations, the point
is always physics, and there's plenty of that in this thread.
Jonathan is requested to peddle his cracked pottery elsewhere.

[Old Man]

[snip diarrhea]


"The aim of science is not things themselves, as the dogmatists
in their simplicity imagine, but the relations among things; outside
these relations there is no reality knowable."

Henri Poincaré, Science and Hypothesis, 1905


I am talking on-topic. You simply can't recognize that fact
since you're so out of date. Tell me, what's it like living at
the turn of the nineteenth century?

Jonathan


When I was younger and thought I knew everything, I felt that anything that
didn't reek of contemporary thought was obsolete and of no value.

Many years later, and a lot of ass-kickings by life, it dawned on me that
the problem was one of perspective. If you strap shot glasses on your eyes,
the view you get is 'new', and it also gives you lots of 'interesting
images'. Nevertheless, like any other mind-set, it is limiting. The
greater secrets are in the quieter truths.

After reading a lot of what you've written Jonathan, I think it's time to
take the shot glasses off your eyes and recognize your own myopia. Any
mind-set which requires the wearer to twist and distort things to fit it's
suppositions, may not be a tool, but in fact may be that wearers rider.

Lot's of better souls than yourself have wrested our current levels of
'wisdom' from chaos, so I wouldn't be too quick to abandon them with only
the thin garments of your 'philosophikal' constructions.

O'