Exercise 1: Paper Clip

Description Case 1:  Paper Clip

     Description

A "Gem-style" paper clip is a            FEATURE:
length of stiff steel wire bent
into three flat, nested loops            WHY:
(Fig. 1) to hold sheets of paper
together when they are inserted
between the loops.

The wire is a 1-mm-diameter
steel cylinder that is 10 cm             FEATURE:
long.  It is bendable in the             WHY:
fingers but stiff.

The first loop (a) is a smooth,
U-shaped turn to the right
that starts 2 cm from the
outermost end of the wire.

The second loop (b) is a                 FEATURE:
U-shaped turn to the left                WHY:
that starts 3 cm farther
along the wire and has a                 FEATURE:
diameter just small enough               WHY:
to fit snugly within the
first loop.

The third loop (c) is another
U-shaped turn to the right
that starts 2 cm beyond (b)
and has a diameter just small
enough to fit snugly within
the second loop (as well as
the first).

The wire in each inner loop              FEATURE:
touches and runs parallel to             WHY:
the outer loop that wraps
around it.  All three loops
lie in the same plane, and
pushing them out of that
plane just enough to slide
several sheets of paper
between them makes the paper             FEATURE:
clip act like a spring and               WHY:
squeeze the sheets together.