Question by : Reopening: Can light potentially move an object physically?
“Tristan”
“for example in space, objects are virtually weightless
i am wondering if light, cud transfer its energy into
another object and move it”
“Zeraphin”
“Yes Radiation Pressure of Light can be used to move
Objects, According to Einstein Relation E = pc Photons
Have a Momentum so Light Reflecting off a Surface
Generate a Small amount of Radiation Pressure, This
Method is Proposed to use on Solar Sails.”
However if solar wind and radiation pressure can be used
to propel an object through space, then how do we account
for those forces which are coming from all directions.
If a sail were postioned to recived these forces from
our sun, how can we overcome the “headwind”. Also, if we
were to overcome the “headwind” then how do we account
for the light coming at us, would this not create a red
shift? and if it were to create this redshift what would
the result be, could it produce gammarays on the object
flying through space?
Aslo, from this how could we specify a direct path? as the light would be transfering its enegery on any surface.
i would like to add that im not only talking about our system. because if we were moving at a high enough rate to increase the frequence of the light waves, im sure we would find a point where the force from the lightwaves behind us and the lightwaves infront of us would be equal,
Best answer:
Answer by David
When I was 8 years old I had a gadget. It was a glass globe (about the size of a baseball) that was sealed so it contained a vacuum. Inside of the globe was a shaft pointing up from the bottom and on top of the shaft was balanced a paddle wheel (for lack of a better description) on top of a pin point. The paddle wheel had 4 fins that were white on one side and black on the other and when you put this device under a desk lamp the wheel would spin and keep on spinning.
My understanding of how it worked was that the light (or heat?) from the light absorbed into the black side of the fins and would push the wheel around and around. There was very little resistance in the system (since it was in a vacuum no wind resistance, and since it balanced on a pin very little friction) because the pressure from the light would not be strong enough to overcome these forces.
So my answer is yes, but I cannot give you the scientific formulas to quantify the effect.
Give your answer to this question below!
2 Responses
A solar sail is only going to work if there is more radiation pressure from a star or a laser on one side than on the other. There are not “forces coming from all directions”, at least, not around here – the light and particles are almost all coming from the sun.
I guess there is a speed limit since as you say the faster the sail goes the more particles and radiation will impact the leading side at high energy, slowing it down. I presume that light reflected from an oncoming sail would be blue-shifted and at relativistic speed be blue-shifted into the gamma – although, now that I think about it, it would hit the sail as gammas and probably go right through, and certainly present a radiation hazard to any crew. Yes, the light from behind would be red-shifted, e.g. as you move away from the sun.
Photons have momentum P = h/L; where h is Planck’s constant and L is wavelength. [See source.]
When photons reflect off, say, a solar sail, as suggested above, we have a change in direction so we have dP = F dT and dP/dT = F which is the force of the impact of those photons on the sail. And that’s what pushes the solar sail forward.
We assume that the photon density over space coming from the Sun is greater than from any other sources, like stars or the Moon.
As you might guess, the force per photon F is very very tiny. But when billions of photons per unit time are striking the wide area A of a solar sail, that adds up to a measurable amount of force over the area of the sail. Solar sail has been suggested as a motive means for interstellar space travel for decades now, reaching way back to the 1940s at least.