Why do some materials feel smooth while others feel rough?

🧠 Detailed Explanation (For Older Kids)

The way a material feels, smooth or rough, depends on its surface texture. Smooth materials, like glass, have fewer bumps and allow your fingers to glide over them easily. On the other hand, rough materials, like sandpaper, have lots of little bumps that make it hard to slide your fingers across. This is why you can tell the difference just by touching them!