Does Sandpaper Increase Friction?

Short answer: finer grade sandpaper has more points of physical contact than rougher grade sandpaper, and each point of contact is a source of friction.

Does sand increase or decrease friction?

Adding a small amount of water to sand can significantly reduce the sliding friction. Everyone who has been to the beach will know that dry sand doesn't make good sandcastles—the grains slump into a puddle when the bucket is lifted.

Does sandpaper have high friction?

From our experiments, we have concluded that the rougher surfaces have a higher coefficient of friction. The highest was sandpaper which had a average coefficient of friction of 1.666. Next was foil, with an average coefficient of friction 1.665. After that, it was felt with a average coefficient of friction of 1.645.