Final answer:
The work done against friction involves overcoming resistive forces during motion, and can be zero, positive, or negative depending on movement direction. Work done against gravity involves lifting objects against Earth's gravitational pull, leading to increased potential energy that is 'given back' when objects come down.
Step-by-step explanation:
Work done against friction refers to the work necessary to overcome the resistive force that opposes the motion of an object. For example, pushing a crate up a ramp involves doing work against friction as you are moving against a force that resists motion. This process typically involves kinetic or static friction, which can do zero, positive, or negative work, depending on the specific situation and direction of movement.
On the other hand, work done against gravity is the work performed when lifting objects or climbing stairs against Earth's gravitational force, which is a conservative force. This work leads to a transformation of energy, with the potential energy of the object increasing as it is elevated. When the object is lowered, gravity does negative work, and the potential energy is converted back, often to kinetic energy if the object is falling freely.