Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: neilep on 05/07/2025 13:38:00
-
Dearest Photonologists,
As a sheepy I of course propel myself through space all the time with my TEMU purchased solar sail
Look here I am in this bona-fide non doctored true picture.
(https://lh3.googleusercontent.com/pw/AP1GczOiuq2p0CclYeG_ntx_c8NoO53XO65cYlCm4yJexjphFZdw-VEstaMbwYmB46yeRIE7OcyakXpmtxTN2NriVet3vi4IJIxaGMUFnqeOn1vDgXfFV3j3=w2400)
Me being propelled by my TEMU solar sail just moments ago !
If photons are massless, how do solar sails still manage to generate propulsion? What fundamental physics allows light, without mass, to exert a continuous propulsive force on a spacecraft?
I reached out to Rod Stewart but he was too busy sailing !
do ewe know ?
whajafink ?
Hugs et les shmishes
mwah mwah mwah
neil
xxxxx
-
If photons are massless, how do solar sails still manage to generate propulsion? What fundamental physics allows light, without mass, to exert a continuous propulsive force on a spacecraft?
Because photons, despite lack of rest mass, have momentum, and it's exchange of momentum that gives thrust to a solar sail.
-
If photons are massless, how do solar sails still manage to generate propulsion? What fundamental physics allows light, without mass, to exert a continuous propulsive force on a spacecraft?
Because photons, despite lack of rest mass, have momentum, and it's exchange of momentum that gives thrust to a solar sail.
Thank you Halcy....still confused a little....if the photon has no mass then where does the momentum come from ?
-
Thank you Halcy....still confused a little....if the photon has no mass then where does the momentum come from ?
My very non-technical way of looking at it, light has no mass but overall energy is mass+momentum so in the case of photons just momentum. When they hit the sail they stop moving so the energy is transferred to the sail.
-
Thank you Halcy....still confused a little....if the photon has no mass then where does the momentum come from ?
Momentum is γmv which is singular (∞ * 0, which is undefined) for a photon, so inapplicable.
The momentum of a photon is h/λ (Planck constant / wavelength), which is not singular.
light has no mass but overall energy is mass+momentum so ...
Adding zero (mass) to anything is pointless, and energy and momentum are different things with different units, but yes, energy can be expressed as hc/λ. That says that energy is proportional to momentum for massless things like photons, and is the same numeric value if using natural units where c is 1.
-
If photons are massless, how do solar sails still manage to generate propulsion? What fundamental physics allows light, without mass, to exert a continuous propulsive force on a spacecraft?
Because photons, despite lack of rest mass, have momentum, and it's exchange of momentum that gives thrust to a solar sail.
Thank you Halcy....still confused a little....if the photon has no mass then where does the momentum come from ?
Its energy. The idea that momentum can only be associated with mass was found to be incorrect over a hundred years ago.
-
One derivation is ascribed to Einstein. Essentially a matter of dimensional analysis, which shows that a change in energy density is equivalent to a transfer of momentum.