IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Objective

To get a feeling of the phenomenon of weightlessness.

Introduction

An effect of the weight is extension in a slinky. As you must have experienced, a slinky is like a spring but the turns are very flexible and even without a load, it can extend to several times of its natural length under its own weight. If you hold few turns of a slinky in your hand and let the rest of it hang from there, the hanging part also extends through large distances. This extension again is because of its weight. If the effect of weight can be reduced to zero, the slinky in a vertical position will not extend.

Procedure

1. Hold few turns of a slinky in one hand. Let rest of it hang vertically. The hanging part will be extended. By holding appropriate number of turns make this part about 10 cm.
2. Now leave the slinky and let it fall. You may catch the falling slinky at some lower level. The extended turns all shrink.
3. You may do it several times to show the effect clearly. The slinky shrinks because in the frame of the falling slinky, there is no effect of gravity.

Discussion

We say the slinky has become weightless as measurable effects (i.e., extension of the slinky) of the weight have vanished.

Note

You can also perform this demo with a spring-mass system. The spring should have small spring constant so that there is a large visible extension when you hang a load. Dropping it will shrink the spring.