How do solar sails work?

Question

I know what you are going to say, “google it”. But according to google, solar sails work by harnessing the light. each particle of light has momentum, and it uses these to accelerate. but i thought that momentum was equal to mass times velocity, and according to the laws of physics and einstein’s law of relativity, photons have no mass? therefore their momentum is 0 because 0 times the speed of light is 0? i am confused, am i missing something?

Answer 1

God does it.

Answer 2

Physics says light has 0 rest mass.



Rest mass is the mass of an object when not moving relative to something else...



Since light always moves relative to something else moving at less than light speed it has NO REST MASS



it does have RELATIVISTIC MASS that is the mass an object has from moving very fast..



So you get an A for effort but D on comprehension

Answer 3

Very similar to a wind which consists of massive atoms of gas colliding with the atoms in the Sail.

Hence its a radiation wind of massive particles of light(not photons because they don't exist since they have no mass or volume). The idea of the photon being light with no mass or volume has been the most misconstrued in science.Even though" photon" is the Greek word for light. It could have been called LUZ.



Linear Momentum can be defined as Energy per unit velocity. Hence if at rest a mass has no velocity ,then it would have no kinetic energy,no kinetic energy =no momentum.



To assume that Light particle without energy has momentum is simply absurd.

Answer 4

Sun light has a momentum. It falls on the sail and gets absorbed. Its velocity becomes 0. The momentum from the sunlight is tranferred to sail. h nu/c² is the kinetic mass. This gives

h nu /c as the momentum. This much momentum is given to the sail. it has move backward. Her nu is the frequency and c is the velocity of light.

Answer 5

p = mv is classical mechanics.

Relativity says that actually, p = γmv. Since γ is infinite for an object traveling at the speed of light, this expression becomes the useless "infinity times zero," which could equal any number.



(Note: I am using "m" for rest mass because I can't write subscripts here. And because the concept of relativistic mass m = γ m0 just so you can still say p = mv is stupid, even if it does make the following equation pithier.)



Other relativistic equations helpfully inform us that momentum is related to energy.

E^2 = (pc)^2 + (mc^2)^2

So when m=0, p = E/c.

Photons do have nonzero energy, so they must also have momentum.

Answer 6

Photons have momentum.

There have been different explanations over the years,,,, Rest mass plus relativistic mass is one of them.

In which the rest mass of a photon is zero but it has a relativistic mass.



A different one is that momentum is NOT mv. That is an approximation used for low velocities.

The momentum of a photon is p = h/lambda



However the one thing that is not in doubt is that each photon contains momentum.

Therefore a force is created. Number of photons * momentum per photon/ time elapsed.

Answer 7

Solar sails absorb light (sunlight) and the transfer of heat exerts pressure on them. This can be understood by studying radiometers. There are at least three types of radiometers (Nichols vacuum, Crookes imperfect vacuum, and MEMS electrostatic charges, magnetic moments, surface tension, and viscosity). Don't confuse MEMs nanotechnology with molecular nanotechnology devices that use surface chemistry. Assuming that the solar sails, in question, exist in the vacuum of space, they operate on the principles of a Nichols radiometer (which uses the principle of dispersed heat, rather than absorption of photons). The common myth is that photons turn a Nichols radiometer. If this was so, it would turn the opposite direction, since photons would be absorbed by the dark side and reflected off the light side of the metal. Instead, the Nichols and Crookes radiometer work by the transfer of heat. They turn in opposite directions due to the amount of vacuum.//////PHOTONS HAVE MASS, BUT NO REST MASS. Photons can't stand still, and must travel at the speed of light. Photons also have momentum.

Answer 8

So that's the point when you're supposed to google "why do photons have momentum" to continue with your quest??



To spare you the trouble of going face-to-face with Google



Einstein's expanded energy-momentum relation says E^2 = (mc^2)^2 + (pc)^2

When m=0 as in the case of a photon, E = pc

And since E = h*f = h * c / lambda for light

hc/lambda = pc

p = h / lambda

i.e. photons with higher frequency (and more energy) carry more momentum

Answer 9

Your confused. If the speed of light was 0 then we wouldn't be able to see the sun and the stars.

Answer 10

Photons do not have zero mass, they have zero Rest Mass. Since photons are never at rest, light sails might work, if someone makes one someday.

Answer 11

Light has energy that can be converted into inertia. Albert Einstein said energy is mass

Answer 12

With all the other answers it is worth pointing out that the amount of momentum carried by light is very small, so not much surprise that it was missed by classical physics. The only reason it can work is that in space there is no air resistance and so a small but continuous input of momentum eventually builds up to a worthwhile velocity.

Answer 13

Allow for relativity.



E = mc² tells us energy and mass are equivalent in some way.



Think of the 'equivalent' mass of a photon as: m = E/c²



Momentum = equivalent mass x velocity = (E/c²) x c = E/c



This is the correct formula for the momentum of a photon, though I've 'fudged' the physics!