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July 28, 2014

Homework Help: Physics please check

Posted by Mary on Tuesday, April 24, 2007 at 5:44pm.

For the highest accuracy, would you choose an aluminum or a steel tape rule for year-round outdoor use?

a. steel tape rule

b. either of the two

c. aluminum tape rule

Why?

I am not quite sure what this question is asking.

I took an educated guess of steel because all the number are less based on the following information. The less something expans the more accurate its graduations for its reading will be.

Steel Aluminum
thermal cond. 14J/(s.m.C) 240J/(s.m.C)

specific heat 452 900

coeff therm.exp .000023 .000012


I agree. The question is asking what material will be least affected by outdoor temperature variations

I am reminded of a lab I had all my Physics classes do: To try to determine the linear expansion of a concrete sidewalk (no expansion joints were in it, non-professionals laid it), it was about 300 feet long. I had the students measure it with a steel rule in August, when the temp was near 100F, and measure it again in Jan, when the temp was near 30F with the same steel rule. So the question is, what was the change in the rule, and in the concrete. You may want just do the rule changes for an exercise,,,,it is enlighting as to what just is a measurement, and what does it mean?

I think this answer was wrong although I didnt see the correct answer. The question is asking for the material leasr affected,thus, based on the coefficients of linear expansion, we can say that aluminium is more prone to expanding more compared to steel. The coefficient of linear expansion for steel is 12x10^-6 ,hich less than 23 x10^-6 for steel.

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