Re: Can inverse gravity waves cancel out Earth's gravity in selected areas?

Hello Sal and Sue,

Are you both telling me that radiation pressure can be caused by
massless photons? Because energy reacts with matter? Has anyone ever
heard that light sometimes acts as a wave and sometimes acts as a
particle? I have a hard time understanding how energy can apply a force
if it has no mass. I apologize for my ignorance, but I would like to
learn. In my simple mind, the reaction in matter to light is heat. Is
that heat from the matter or from the light? I am not good in math
either and Sue sent me to a link that used variations on E=mc(squared).
http://farside.ph.utexas.edu/teaching/em/lectures/node90.html In my
mind m is mass which can be converted to E (energy) and back again. How
does that relate to radiation pressure?
sal wrote:
On Wed, 18 Oct 2006 08:59:19 -0700, Mike wrote:


Igor wrote:
Mike wrote:
TrekJunky wrote:
Hello Sue,

I would like to answer you question about how I would measure the
mass of light. I would like to approach it by stating a few facts to
see if you agree with them:

Light has no mass, or if it has some it is beyond any measurement
accuracy.

1) Solar Sail space ships are propelled by the pressure of light on
the "sails" not solar wind(subatomic particles) as some might think.

That is not your usual notion of pressure.

Why not? Light has momentum. Momentum changing direction exerts force.
And force per unit area is pressure. It's that simple.


Idiot. Are you the sam eposter asking these stupid questions? How do you
make light change direction other than making it pass through a gravity
field?

Well, as one example, a mirror works pretty well.

And by the way, that's what a solar sail is. In the simplest case of the
sail perpendicular to the incoming light, the photons reverse direction
when they hit the sail, their momentum flips sign as a result, and the
sail gains twice the momentum of each photon in the process.

The sail feels a force as a result of reflecting the light, and if someone
on the ship measures the force on the sail as a whole and divides by the
area of the sail, they find the radiation pressure which is being exerted
on the sail.


--
Nospam becomes physicsinsights to fix the email

.

Relevant Pages
Loading