Challenge your students to tie the best knot. Different knots stress the string at different points, either spreading out the stress or centering it on one point. Have your students practice different ones to figure out which ones hold the most weight.
Teachers, you will need a rod/pipe that will not break to tie the strings to. Then you'll need a spool of thread, a ball of yarn, or a spool of very light fishing line. Have students practice knots, then tie them in front of you, and then use a b