Does light have inertia?
When you get into relativity, precisely defining inertia gets a little tricky. Mass is defined not as inertia but as the energy of a particle at rest. Light, which is never at rest, has zero mass. An equation like F=ma can’t really apply to a massless particle. Light does carry momentum, though. So in a conceptual sense at least, light does have inertia. If light runs into something, it’s going to impart an impulse (so what john says above is correct as a practical matter).
