# Linear expansion coefficient of glass

Given: The linear expansion coefficient of glass is 9 × 10−6 (◦C)−1. An automobile windshield has dimensions of 60 cm by 400 cm. What minimum spacing around the wind-shield is needed to prevent the windshield from breaking if the temperature changes by 150◦F? Answer in units of mm.

I understand I use the equation alpha*Length*delta(t) but it won't pop out the right answer and I think the dimensions are what is throwing me off. Any advice is appreciated!

Doc Al
Mentor
Show what you did. I would have chosen the 400 cm dimension to work with, as it will change the most. Did you convert the temp change to degrees C?

I did not change to degrees Celsius. The conversion is (5/9)*(150-32) so my new temp is 65.556. Also, I have to change cm -> mm. so the dimension would be 4000 mm. So, my final equation would be (9e-6)(4000)(65.556) ??

Doc Al
Mentor
So, my final equation would be (9e-6)(4000)(65.556) ??
Yes, but don't forget that that's the total increase in that dimension. So what minimum spacing would you need at each end?

My answer from that comes out to be 2.36 but I don't know how to find the minimum spacing piece that you're talking about.

Doc Al
Mentor
If the entire glass expands by 2.36, how much space do you have to allow at each end?

the given dimensions + expansion value.

so i dont know if you allready figured out your problem.... but i just did that exact problem. the error that you made was that the temp that is given is a (delta t). to convert from F to C it is just (delta t)*(5/9).... you dont subtract 32. that should fix it! after that it is just: