I'm trying to understand the concept of work. I understand that no work can be done by a force if there is no displacement, but I have got confused about whether a force has to cause the displacement. The site physicsclassroom.com says this: But a mentor on this site says this: This latter point seems reasonable to me since, if I raise a body with my hand then it is said that gravity has done negative work on that body; and gravity certainly hasn't caused the displacement. Could anyone clarify please? Thank you.