If I had a flashlight in a zero-G vacuum environment, infinite battery and switched i

To clarify, this would be the galaxy's crappiest ion drive equivalent. Since ion drives eject ions to generate thrust, the force generated is tiny, but will continuously accelerate an object in the vacuum, I want to know how long a flashlight ejecting photons would do the same, since it does have a tiny amount of force that's exerted onto the flashlight when the photons are ejected, being Newton's Laws and somesuch.

To make it simpler - Any weight of flashlight and luminosity can be used, but I'd rather not have some kind of super light flashlight with ultra-luminosity. Just a flashlight that you can pull off of a shelf in a store.

The batter weighs as much whatever batteries are used in the model of flashlight, but do not change in mass as they run and do not run out.

The environment is a perfect vacuum with as little gravitational influence as possible.

How long would it take to accelerate this flashlight to 350m/s? (approx. the speed of sound in dry air)

How long will it take to accelerate the flashlight to near-lightspeed?

How long will it take to accelerate to 120km/h? (highway speed)

I read about it somewhere that no matter how heavy a spacecraft is, if there is no outside influence heavier than a flashlight, then pointing a flashlight out the *** end will eventually cause acceleration, even if it's millenia from now. It's not meant to be practical. Just to make people go "Cool" that a flashlight could theoretically propel a spacecraft.

I'd do this myself, but I flunked math.

It's actually a photon drive. photon at project Rho

A 3W LED is about 30% efficient at turning electricity into photons, so you get 1W of photon exhaust, or 1/300000000 Newtons. This is a very small force.

Two posts because tablet. What is a Newton? It's force that would accelerate 1kg by 1 m/s. If you hold a small Apple (0.11kg or 3 oz) against Earth gravity, that's 1 Newton force upwards. Not much!


My Quark Mini weighs about 80g with a battery. So 1/300000000 N accelerates my flashlight at four ten millionths of gravity. Wow.

Pluggging those numbers without questioning them into Calctool gives an answer of 0.00000000416666 m/s^2 or 0.00000000000416666 km/s^2 (4.16666 E-12 km/s^2)

4.16666 e-12 multiplied by the number of seconds in a year (365X24X60X60) = 1.313997898 e-4, still a thousandth of a kilometer per hour after one year of acceleration.