Physicists in 18th and 19th centuries, developing the newtonian Mechanics, defined the mechanical energy of a particle (a point body with inertial mass m).
In particular, they stated that, if a particle is at the point P of a conservative field, a scalar function of the position r of P can be defined, usually denoted by V(r), said potential, and the mechanical energy of the particle in position r and with velocity v is given by the sum of two functions:
If we introduce the quantity p, said momentum of the particle, defined as
the (1.1) may be written as
and the (1.3) may be written as
From Newton's laws it follows that the energy of a particle moving in a conservative field is constant.
Because the energy is condensed in the particle, the motion of the particle implies a flow of energy.
For example, the energy of a bullet at the mouth of a gun flows due to the motion of the bullet and when the bullet hits the target, if the collision is anelastic, the energy spreads within the target as heat.
Therefore we can say that the energy can propagate due the motion of one or several particles.