Is there any way to use light as a motive force ?

Photons don't have rest mass, but they absolutely carry momentum and energy. So if you shine a light one way, you are propelled the other way. What's more, because they travel at the highest possible speed, light gives you a better momentum per energy ratio than any other kind of rocket. Photon drives may soon be practical for lots of space applications that need to maximize this efficiency.

Light Sails. This is an old science fiction means of space propulsion. I remember one story I read about aliens that relied on this technology for space travel, and judged planets as animals or not by whether they had the ability to produce a technology for producing a propulsion system to move the alien ship. If the encountered planet couldn't provide the energy required (create a light gun), the aliens would zap the sun and cause it to go nova to give them the energy they needed. Probably a Larry Niven story but I really don't remember. Basically it isn't a new idea, is all I am trying to say.

Solar sails use light for propulsion, and they are the subject of serious research. Look at:

http://solarsails.jpl.nasa.gov/introduction/index....

Though, as others have said, you're not going to the speed of light.

The device that P was thinking about that demonstrates the propulsive qualities of light is the radiometer. Should be easy enough to find on the web.

Light or Photon, being energy(MASS) exerts pressure known as pondermotive force. It is basically dependent on the Energy densitity of the photon. When a photon leaves the source, it exerts pressure/thurst on the source or any particle lying in its field. This phenomenon is well known to atomic physicist and plasma physicsist as well.

Lasers are used for such experiments. Laser based propulsions are experimented and although the experiments are not so successful but in the coming future, there can be a progress.

Further, Photon Drag effect for example(Electrons(charged particles) are dragged by photons(Especially those photons fall in far infra red or Carbon di oxide laser wavelength 10.6microns) is another example of photon thurst.

they have a momentum = h/wavelength

so in principle you could build a great big sail and sail off into the stars.

http://en.wikipedia.org/wiki/Solar_sail

there's a cool device that i forget the name of... it basically is like an Anemometer, except with flat cups. one side of the 'cup' is silver, the other one black, and sits in a vacuum (in a glass orb) and gets pushed around by this pressure (silver side reflects the light, so it gets pushed...). though a cheap one will not work this way, it uses the different gas temperature to push it round (so black side is being pushed by the gas)

can this get you to light speed? no

the pressure also stops the sun from collapsing

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if object A hits object B, it imparts some of its momentum upon B. doesnt matter if A is a photon, electron, atom or a flying turd. a sail should work for all 4.

microwaves and radiowaves are both photons

Yes, in principle you can use light waves as a form of thrust, but it had better be a heck of a lot of light. Pressure from light waves is important in the structure of stars, and causes very small dust particles to spiral into the Sun, but you're unlikely to want to fly a spaceship with it. Under no circumstances will this, or any other force, accelerate a mass to c.

Do photons have thrust? If so, how many would you need to move an object.?

Saw a programme once where a gas (I can't recall it's name) ignited when subjected to Sodium light. That caused an explosion. Maybe you could use that Idea?

You are talking about solar sails.

Have a look at this website which tells you the current facts about this topic.

http://planetary.org/programs/projects/solar_saili...

Light is the emission of photons, as photons don't have any mass you can't get much energy out of them. Which is probably why they can travel so fast. E=MC2 holds good.

In short, no.