Odd that no-one’s answered this. Here’s my guess - If you pull on a straight cable, the force you are applying has pretty well nowhere to go aside from pulling at the socket. The cable is not very elastic - it won’t stretch with the pull.
On the other hand, if you put coils in it, you’ve turned it into a spring with elastic properties. A spring can deform much more easily than a straight cable, so it takes much more force before you get to pulling out the plug.
Other thoughts:
If you put a pulse into a regular cable, it has a small number of ways to distribute that energy. I imagine the main way would be for the pulse to travel as a transverse wave (the cable oscillates perpendicular to its length and the pulse appears as a moving bump). As the pulse hits the end of the cable, it applies the force that knocks it loose.
On the other hand, if you have a coil, you can still have a transverse pulse, but the pulse can manifest longitudinally (coils get closer and farther apart) and torsionally (coil tightens and loosens), and whatever else. Perhaps some of these disturbances in the coil aren’t very effective at loosening it where it’s plugged in, and so it’s a bit more resilient.
I’m sure the designers of the original phone handset cables were just trying to pack a lot of cable into a small space - The plugs clipped in or were permanently attached, so disconnection wasn’t a worry.
Odd that no-one’s answered this. Here’s my guess - If you pull on a straight cable, the force you are applying has pretty well nowhere to go aside from pulling at the socket. The cable is not very elastic - it won’t stretch with the pull.
On the other hand, if you put coils in it, you’ve turned it into a spring with elastic properties. A spring can deform much more easily than a straight cable, so it takes much more force before you get to pulling out the plug.
Other thoughts: If you put a pulse into a regular cable, it has a small number of ways to distribute that energy. I imagine the main way would be for the pulse to travel as a transverse wave (the cable oscillates perpendicular to its length and the pulse appears as a moving bump). As the pulse hits the end of the cable, it applies the force that knocks it loose.
On the other hand, if you have a coil, you can still have a transverse pulse, but the pulse can manifest longitudinally (coils get closer and farther apart) and torsionally (coil tightens and loosens), and whatever else. Perhaps some of these disturbances in the coil aren’t very effective at loosening it where it’s plugged in, and so it’s a bit more resilient.
I’m sure the designers of the original phone handset cables were just trying to pack a lot of cable into a small space - The plugs clipped in or were permanently attached, so disconnection wasn’t a worry.
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