Engineering Explained!! There is a decent chance that during an interview, your interviewer may have a coffee cup within eyesight. Engineers love to take inspiration from what already exists around them and in the case of mechanical engineering interview questions, this means you may end up with a question like the following…
Why are coffee mugs made from ceramics?
There is no trick question here, and a straightforward answer is all that is necessary. This question both confirms your basic understanding of heat transfer and materials, and also ensures that you can suitably apply those concepts to real world applications.
An answer to common “explain this” mechanical engineering technical interview questions should be 30 seconds to a minute long and concise in wording. The answer to this question first requires a bit of subject matter knowledge in that coffee mugs often hold hot liquid (coffee) for consumption. Knowing that baseline detail, a proper response would first highlight your understanding of conductive heat transfer and note that a primary method in which coffee cools down is through conduction of the liquid coffee against the solid coffee mug. Ceramics have relatively low thermal conductivities when compared to say, metals, which means that heat transfer across ceramic materials are relatively slow. This results in a warmer cup of coffee for longer. Additionally, ceramics have micro pockets of air in their structure and because fluids, such as air, generally have lower thermal conductivities than solids, these air pockets in the coffee mug further slow down the heat transfer rate.
Although the above is all that is especially critical to say in a response to the question, it is always best to go the extra step and briefly demonstrate the scope of your technical chops when possible. In this case, you could then note how although the mug will keep your coffee warm, ceramics are relatively brittle, which makes them easier to crack and chip when compared to say, ductile metals. Alternatively, you could draw points to reusable water bottles, which are often made from stainless steel, but perform well in keeping drinks cold because they often have an air or vacuum pocket between an outer and inner wall. This allows the metal water bottle to hold temperatures like that of a ceramic coffee mug but without the associated fracture risks.
