Forces can be categorized into different types:
1) Gravity (Fg) is the force of attraction between objects with mass, directing objects on Earth downward.
2) Friction (Ff) resists the sliding of objects in contact and opposes their motion.
3) Air resistance (Ff) is a type of friction that opposes the motion of objects through the air.
4) Normal force (Fn) supports objects in contact with stable surfaces.