Have you ever had the impression that heavy items of furniture start to take root – that after years standing in the same place, they’re harder to slide to a new position? Do your best wine glasses, after standing many months unused in the cabinet, seem slightly stuck to the shelf? Has the fine sand in the kids’ play tray set into a lump?
If so, you’re not just imagining it. The friction between two surfaces in contact with each other does slowly increase over time. But why?