1. Friction: This is a force that opposes motion between two surfaces in contact. It can be static friction (when objects are at rest) or kinetic friction (when objects are in motion). Friction converts kinetic energy into heat energy, slowing down the object and decreasing its momentum.

2. Air resistance: This is a force that opposes the motion of an object through the air. It increases with the speed of the object and the surface area it presents to the air. Air resistance acts in the opposite direction of the object's motion, slowing it down and reducing its momentum.

It's important to note that both friction and air resistance are examples of resistive forces. They work against the motion of an object and therefore decrease its momentum.