Question

A student is investigating how the extension of spring varied when she changed the force stretching it.

Her ruler is marked only in cm and each mass 100g

She writes the following design for her investigation.
>I will hang 100g on the string
>I will hold the ruler next to the spring
>I will add another mass and measure the length again.
>I will repeat this process until I have enough measurements.

What is the dependant variable?
One important control variable that should be kept same?
Suitably safety precaution along with reason?
How should she convert her measurement of mass into fo