If you ever get stranded on the road without your favorite theoretical mechanical engineering resources you may want to use the following website. It is full of information that will allow you to evaluate whether a particular equation or theory applies and a number of other subjects which are germane to mechanical engineering design. It includes information on a wide range of materials, design, processes, unit conversion, formulas and engineering mathematics. All the content is created by experienced academic and professional engineers. I was impressed and I think you will be too.