Unlike many other parts of structures, which experience combinations of compression and tension, cables support loads purely in tension. Thicker cables are not necessarily stronger than thinner cables. The particular material of the cable, as well as how the cable is formed, determine its strength and stretchiness. In this activity, kids will likely find that sewing thread is relatively weak and that fishing line is strong, with yarn and dental floss falling in between. Kids will probably be surprised at how much weight the different cables can support.
Different uses require cables with different degrees of stretchiness.
For example, the non-stretchy wires that support tall radio towers keep the towers from moving too much. On the other hand, because ship mooring cables are stretchy, they can act as shock absorbers during storms. A fishing line's stretchiness allows it to absorb a sharp but short jerk that would snap a non-stretchy cable. Kids may try twisting or braiding several lengths of cable or wrapping different kinds of cable together. Draw comparisons to the actual methods used in suspension bridges and elevator cables.