would a researcher ever deceive a participant in a way that could possibly cause harm to them if they're not completely aware of what is going on in this study?

I know forensics has a lot to do with psychology as well as science, in this case its utilizing both concepts.

so in terms of science and psychology studying and observing behavior, like emotions can be viewed as scientific because it's a natural occurrence that can be written down and described.

how is systematic observation used in psychology?