Periodic Signal
Above is an example of a periodic signal: $ y(t) = \sin(\pi t) $
The function is periodic because as can be seen from the graph $ y(t+T)=y(t) $ where T=2 seconds.
Non-Periodic Signal
Represented above is an example of a non-periodic function: $ y(t)=sin(10 \pi \ln(t)) $. This function is clearly not periodic because the frequency changes with time and therefore $ y(t+T)\notequal y(t) $.
