Concrete sidewalks are always laid in sections, with gaps between each section. For example, the drawing shows three identical 2.4 m sections, the outer two of which are against immovable walls. The two identical gaps between the sections are provided so that thermal expansion will not create the thermal stress that could lead to cracks. What is the minimum gap width necessary to account for an increase in temperature of 27 C°? http://www.webassign.net/CJ/p12-20.gif (here is a picture) I used the equation (deltaL=alpha*Lo*deltaT). So I knew alpha was 12*10^-6 and Lo was 2.4m and deltaT was 27 C°. I got deltaL to be 7.776*10^-4 m. So the concrete expanded and how has a length of 2.4007776 m. After that I wasn't sure what to do. I thought it would be 3 times 7.776*10^-4 but it wasn't. Could you please help? Thanks so much!!!