Temperature and stress question

[pinky2468]

Last question for the semester, but Physics II is right around the corner!
This is an easy question but I am not sure how to answer it!
A steel ruler is accurate when the temperature is 25 degrees celsius. When the temperature drops to -15 degrees celsisus the ruler no longer reads correctly, but it can be made to read correctly if a stress is applied to each end of the ruler . Should the stress be compression or a tension? Why?

I think the answer is tension, but I really have no idea why! Thanks!

 

[dextercioby]

Last question for the semester, but Physics II is right around the corner!
This is an easy question but I am not sure how to answer it!
A steel ruler is accurate when the temperature is 25 degrees celsius. When the temperature drops to -15 degrees celsisus the ruler no longer reads correctly, but it can be made to read correctly if a stress is applied to each end of the ruler . Should the stress be compression or a tension? Why?

I think the answer is tension, but I really have no idea why! Thanks!

The answer is right,and the explanation is simple.Cooling the ruler makes it shorter (experiments show that dilation/contraction is linearly dependent on the temperature,but for reasonably small chages in temperature (i guess your 40 would fit the linear approx.)),so you'd have to pull (very hard actually) both ends to lengthen it back again.That "pulling" is force which tensions the ruler.

Daniel;

 

[wais]

You are correct, the stress should be tension. This is because when the temperature drops, the steel ruler contracts and becomes shorter, causing it to read incorrectly. By applying tension to the ends of the ruler, it will stretch and become longer, compensating for the contraction due to temperature change. This will allow the ruler to read accurately again. Compression, on the other hand, would only make the ruler shorter and worsen the reading error. This concept is known as thermal expansion and is an important factor to consider in many real-world applications, such as building bridges and railways. Hope this helps and good luck in Physics II!