California Science Test (CAST) 8th Grade Practice Exam

When an object moves by sliding across a surface, the force that opposes that motion is friction between the surfaces. Sliding friction acts opposite to the direction of travel, and as the object slides, it converts some of its kinetic energy into heat, causing it to slow down. This is the typical decelerating force for objects in contact while sliding.

Air resistance can slow objects moving through air, but it’s different from the friction you feel when two surfaces rub together. Mass isn’t a force itself; heavier objects have more inertia, which affects how hard it is to change speed, but mass doesn’t by itself slow a sliding object. Tension is a pulling force and isn’t the general force that slows sliding motion.