Solving a Convolution Problem
When you slide a rectangular signal over another rectangular signal and take the area under the curve, i.e., perform convolution, at first there is no overlap. Then, the overlap gradually starts increasing in a linear fashion. When the two rectangular signals are exactly on top of each other, that is the point of maximum overlap. After than, there is a gradual decrease until there is no overlap. The resulting convolution signal is then a triangular signal.

Update: A rectangular signal is given by
\begin{equation*}
\prod (t) =
            \begin{cases}
1 &amp;  0 \le t \le 1 \\
0 &amp; otherwise
            \end{cases}
    \end{equation*}
Its convolution is given by
$$z(t) = \int _{\tau=-\infty}^{\infty} \prod(\tau) * \prod(t-\tau) d\tau$$
which turns out to be
\begin{equation}
z(t) = \begin{cases}
0 &amp; -\infty \le t \le 0 \\
t &amp; 0 \le t \le 1 \\
2 - t &amp; 1 \le t \le 2 \\
0 &amp; 2 \le t \le \infty
\end{cases}
= \Lambda(t)
\end{equation}