$4\mathrm{.}1$ Define the term bending moment.

$4\mathrm{.}2$ A light uniform beam ABCDE is $13$ metres long and is supported at A and $D$ as shown below.

Calculate the following:

$4\mathrm{.}2\mathrm{.}1$ The reaction forces at support A and $D$

$4\mathrm{.}2\mathrm{.}2$ The bending moments at points $B,C$ and $D$

$4\mathrm{.}2\mathrm{.}3$ Draw a shearing force and bending moment diagrams and show ALL the principal values or main values in both diagrams. $($NO marks will be allocated if main or principal values are NOT indicated on both diagrams.$)$