Fill in the blanks:
$1.$ The ratio of displacement at any position and ....... remains constant for a particle executing $SHM$.
$2.$ The radius of the reference circle is equal to the .......... of the oscillator.
$3.$ Increase in phase per second of $SHO =$ ......... .
$4.$ $SHO$ covers ......... distance in one periodic time.

(A) $1.$ The ratio of displacement $x$ to acceleration $a$ in $SHM$ is given by $x/a = -1/\omega^2$,which is constant. Thus,the ratio of displacement to acceleration is constant.
$2.$ The radius of the reference circle represents the maximum displacement from the mean position,which is the amplitude $(A)$.
$3.$ The phase of $SHO$ is $\phi = \omega t + \phi_0$. The rate of change of phase with respect to time is $d\phi/dt = \omega$,which is the angular frequency.
$4.$ In one complete oscillation (periodic time $T$),the particle moves from mean to extreme $(A)$,extreme to mean $(A)$,mean to other extreme $(A)$,and back to mean $(A)$. Total distance $= 4A$ (four times the amplitude).