Final answer:
Sliding friction acts in the direction opposite the motion of the cereal box you are pushing across a tabletop. This force is known as kinetic friction and is typically lower than static friction, which you need to overcome to start the motion.
Step-by-step explanation:
As you push a cereal box across a tabletop, the sliding friction acting on the cereal box acts in the direction opposite of motion. This is because sliding friction is a force that opposes the movement of objects sliding against each other. While pushing on the box, you may initially encounter static friction, which must be overcome to start moving the box. Static friction increases to equal your push but in the opposite direction. Once the box starts moving, the friction you experience is kinetic friction, which is generally less than static friction.
The force of friction depends on the materials in contact and the normal force, which is the force exerted by a surface that pushes on an object in response to its weight. The coefficient of friction is a measure of how much frictional force exists between two objects. If you were to add mass to the box or change the surface by lubricating it, the amount of force required to overcome friction and keep the box moving would change accordingly.