Chapter 8, Problem 56GP

* Eiichi has purchased an adjustable hand grip to use for strengthening hands, fingers, and wrists. The hand grip consists of two handles that can rotate around a common axis and a spring that connects the handles (see Figure P8.56 ). The force needed to squeeze the hand grip can be adjusted from small (Figure P8.56a ) to large (Figure P8.56b ) by changing the position at which the lower end of the spring is hooked to the left handle. Eiichi, Yuko, and Lars have different explanations for why it is harder to squeeze the hand grip in case (b) compared to (a).

Eiichi: It is harder to squeeze the hand grip because the distance between the axis of rotation and the point where the force is exerted on the left handle by the spring is larger in case (b) than in case (a).

Yuko: It is harder to squeeze the hand grip because the extension of the spring in case (b) is larger than in case (a).

Lars: It is harder to squeeze the hand grip because the angle $\theta$ in case (b) is smaller than in case (a).

First, comment on the students’ explanations and decide whose ideas are correct and whose aren’t. Then construct a complete correct explanation. Indicate any assumptions that you made.