At this point, you should be comfortable calculating the work done as an object moves through a displacement by three different types of forces: a constant force, the gravitational force, and the spring force. You should also be comfortable determining whether the work done by a particular force is positive, negative, or zero. As we will see, knowing the sign of the work done by a force on a system indicates how that force is transferring the energy within a system or between a system and its environment.