Dear student,
Here are a few differences between square root spiral and number line:
(i) A square root spiral is in the shape of a spiral whereas a number line is a straight line.
(ii) In a square root spiral, the numbers marked are square roots of positive integers. In a number line numbers marked are real numbers, positive as well as negative.
(iii) Only positive numbers are represented on square root spiral whereas in a number line all real numbers can be represented.
Regards.