# Calculating the force imparted on an object by a laser [duplicate]

It has recently been mooted that micro-satellites could be propelled to nearby stars through the use of powerful, ground based laser systems. However, given that light has no mass, I don't know how to calculate the force exerted by a laser on an object and Google has been relatively little help.

Consequently, is there an easy way to calculate the force exerted on an object by a laser given the power, frequency, distance, albedo of the impacted material etc.

• The immediate place to go is the Wikipedia page on radiation pressure. Is there some specific part of that which you find confusing? May 2, 2017 at 16:15
• Hi James. The question I've linked is essentially a duplicate of yours since both questions ask about the force exerted by light. May 2, 2017 at 16:32

Relativistic energy is:$$E^2 = (m_0c^2)^2 + (pc)^2,$$ For light, rest mass is obviously $0$, so $E^2 = (pc)^2$ and $E = pc$. You can substitute $E = hf$ here, and that gives you the momentum of light. Combine this with the number of emitted photons per second from a LASER, and Using this and some simple maths you should be able to work out the rest.
• Substituting $E=hf$ will give you the momentum transfer corresponding to a single photon, without saying anything at all about the total force. May 2, 2017 at 16:21