Hooke's Law states that the restoring force of a spring is directly proportional to a small displacement. Students in physics class were conducting an experiment to determine the difference in displacement among various springs. They wanted to determine if displacement not only varied with mass but also with the type of spring used. The class tested twenty springs; they varied in length, circumference, and material. They used an assortment of masses as well.

On some springs they used masses of 5g increments; on others, masses of 10g increments. After hanging the masses from each spring, they measured how far the springs streched. The students concluded that thin, aluminum springs had greater displacement than short, thick, iron springs.
As a last experiment, the students decide to compare a short, thick, aluminum spring to a thin, iron spring. Which of these will have a stronger restoring force?

A) The thin, iron spring.
B) The thick, aluminum spring.
C) The restoring force for each spring will depend on the mass used.
D) It is impossible to say because they are adjusting multiple variables.