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Q & A: Tension of springs when cold

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Most recent answer: 10/22/2007
Q:
Can I increase the tension of a spring by lowering the tempature?
- Roger W. (age 40)
Coral Springs,FL USA
A:
Hi Roger,

Yes, the tension in a spring may go up when it is cold, but it also depends on a few other things.

A spring will have tension in it if it is being pulled on on its sides -- if it is just sitting on a workbench, it will have no tension in it and its length will be its "relaxed" length. This relaxed length will be (typically) shorter when the spring is cold because things usually contract when cooled and expand when warmed. If you pull on the spring, it will get longer, and the tension is related to the difference between the relaxed length of the spring and the actual length of the spring while it is being pulled on.

So, if you hold a spring between two fixed posts that put the spring in tension, then the tension should rise in the spring as it gets colder (the posts shouldn't get closer together as they get colder, too, however).

This is a common feature in engineering. Most objects have some springiness to them. Telephone wires hanging from poles typically have more tension in them in the wintertime because they are shorter, but the poles are the same distance apart (these aren't really springs, but the tension rises for the same reason). Bridges too must have movable sections so that when the road surface contracts in the winter cold, the tension in the concrete doesn't get so high as to crack it (concrete has a very high strength in compression but breaks much more easily under tension).

Cooling a material also may change its spring constant. Most materials get more rigid when cold, and this can make the spring require more force to stretch when cold than when warm. Some materials become very brittle in the cold and may break when stretched when very cold (many Van demos involve immersing normally flexible objects in liquid nitrogen, after which they may be shattered like glass). A metal spring when very cold may fatigue easily and develop lots of little cracks in it, changing both its relaxed length and its spring constant.

One peculiarity that you may find interesting is that rubber bands behave oppositely to most other springs. As they cool, they lengthen a bit.

Tom J.

(published on 10/22/2007)

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