Why Do Some Materials Feel Slippery?

Imagine you're trying to hold a smooth rock in your hand, but it feels like it's sliding away, that's what happens when a material is slippery. Some things are smoother than others because of how tiny they look up close. Like a piece of glass has no little bumps or ridges, so it feels really easy to slide across. On the other hand, if you touch something rough like sandpaper, your fingers feel all bumpy and stuck. Slippery materials help us do things like write on paper easily, or make ice skating fun!