In quantum mechanics, there is a phenomenon called the 'Casimir effect'. As two metal plates have a very small distance, the plates work as a potential well, causing limited wave function between the plates while outside doesn't. As a result, two plates have a attraction force. (In some case it could be repulsive but that another story.) In this case we can assume that the plate works as infinite potential. But what if one of the plates are not infinite potential wall? Would sum of Casimir force be non-zero quantity?
For example, let's assume that potential is as follows.