I know the speed of light is 3*10^8m/sec. And its acceleration is Zero. 1. I think we can take photon as light. Its mass=0, acceleration=0, charge=0. By eqn F=ma=0*0=0 i.e any particle with or without mass cannot impel force on a photon. From Newtons third law vice versa is also true. I think force between particles (attraction or repulsion) represents their interaction with each other. Then what is this absorption of photon i.e interaction by jumping electrons(containing mass) actually mean. 2. When a photon is released, is its speed is instantaneous with a speed of light?? If it is instantaneous could you tell me, how does it attain that speed from the start i.e at t=0. If its not instantaneous, Is photon accelerating for its first second to attain the speed of light, since speed is 3*10^8 m for each second , and then it continued to travel with no acceleration after t=1. I dont know the physics too deep. I just know the basics. I am trying to learn into its depths. So please notify me if there are any wrong in my questions.