Will grains of sand or pebbles move quickest?

Grains of sand will generally move quicker than pebbles when subjected to wind or water flow. This is because sand is smaller and lighter, allowing it to be easily lifted and transported by moving air or water. Pebbles, being larger and heavier, require greater force to move and are more likely to remain in place. Thus, in most natural conditions, sand will travel faster than pebbles.