A<unk><unk>  can be of any size in which case its 'strength' A is defined by duration multiplied by amplitude. The graph of the<unk><unk>  is usually thought of as following the whole x-axis and the positive y-axis. (This informal picture can sometimes be misleading, for example in the limiting case of the sinc<unk> .)
Despite its name, the<unk><unk>  is not truly a<unk> . One reason for this is because the<unk> s f(x) = δ(x) and g(x) = 0 are equal everywhere except at x = 0 yet have integrals that are different.  According to Lebesgue integration theory, if f and g are<unk> s such that f = g almost everywhere, then f is integrable if and only if g is integrable and the integrals of f and g are identical.  Rigorous treatment of the<unk><unk>  requires measure theory or the theory of distributions.
The<unk><unk>  is very useful as an approximation for a tall narrow spike<unk>  (an impulse). It is the same type of abstraction as a point charge, point mass or electron point. For example, in calculating the dynamics of a baseball being hit by a bat, approximating the force of the bat hitting the baseball by a<unk><unk>  is a helpful trick. In doing so, one not only simplifies the equations, but one also is able to calculate the motion of the baseball by only considering the total impulse of the bat against the ball rather than requiring knowledge of the<unk> ils of how the bat transferred energy to the ball.
The<unk>  was named after the Kronecker<unk> [citation needed], since it can be used as a continuous analogue of the discrete Kronecker<unk> .
Dirac delta function
Trigonometric functions
Moro reflex
Otalgia classification
Bezold-Jarisch reflex
Optokinetic reflex
Dizziness classification
Acoustic reflex