I plan to drop a torch out of the space shuttle. This torch will have a light-sail out the front, anchored to the torch. When I turn the torch on, it will push itself along with the sail. PS: I am not Abhi, I'm just a very bored boy!
I assume this is a british torch and not an american one. British torches run on batteries, and american torches run on fire Please Register or Log in to view the hidden image! -IggDawg
'fraid not! As the light hits the light sail, the light sail will accelarate in the direction of the light-beam. However, as every action has an equal and opposite reaction (and all that), the torch will accelarate away from the light sail by the same amount. There is no resultant accelaration. Newton said mass (in this case the torch and sail together) will not change their momentum unless acted on by an external force. Think of it as a boat in calm waters with a fire hose and a wall on top. As the water is pumped out of the hose, it pushes the boat backwards but as it hits the wall it pushes the boat forwards. PS Well done USA in the World Cup! Now it's England's turnPlease Register or Log in to view the hidden image!
Actually, guess what: it will work! Please Register or Log in to view the hidden image! The flashlight emits a photon. The sail (1) stops the photon, and (2) re-emits or reflects the photon in the opposite direction. The (1) action would cancel out with the flashlight, but the (2) action will actually have a propulsive effect. Though the most straightforward way would be to just dispense with the sail and just emit the photons out of the flashlight. That way, the photons move in one direction, while the flashlight in the opposite. Kinda like a "light rocket", except the impulse you'll get would be so tiny it'd take you forever to achieve any significant velocity.
But you could get close to light speed in a few billion years if your battery and bulb (all the stuff) holds up that long....
