摘要
A gun, with its explosive energy, can accelerate a bullet, with mass m, from zero velocity. After a bullet is shot into a wall, the wall receives energy, which is converted from explosive to kinetic energy of the ball, and then, to heat and/or deformation energy of the wall. When a person carries this gun in a moving vehicle, and shoots at a wall, the observer witnesses the bullet gain kinetic energy compared with the original scenario. From where is the additional energy derived？ Is the explosive energy of the gunpowder a frame-of-reference-dependent quantity？ Does it concern the theory of relativity by Albert Einstein？ In this article, the additional energy e is defined as the mutual energy of relative motion, which is a flame-of-reference-dependent energy, and thus, may be transferred from one reference frame to another.
