They both refer to a reason (or reasons) for acting. However, "motive" refers to a specific reason for doing a specific thing. It is also more often used in a negative light (as in Law). "Motivation", on the other hand, is used to refer to the general concept of having a reason to do something, and is used more positively. For example: "What was her motive for killing her husband? The jury can't make a decision without knowing her motive." "Do you have ulterior motives?" "What's your motivation to wake up every morning?" "You need a good personal trainer. They'll give you motivation to exercise and stay healthy."