Posted: November 11, 2012 by Wildcat in Uncategorized
Tags: , , ,

You’re not just imagining it, objects really are harder to shift the longer they sit there. A pair of scientists think they have discovered why. 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? A paper by two materials scientists at the University of Wisconsin in Madison, USA, suggests that the surfaces could actually be slowly chemically bonding together. There are already several other explanations for this so-called “frictional ageing” effect. One is simply that two surfaces get squashed closer together. But a curious thing about friction is that the frictional force opposing sliding doesn’t depend on the area of the contacting surfaces. You’d expect the opposite to be the case: more contact should create more friction. But in fact two surfaces in apparent contact are mostly not touching at all, because little bumps and irregularities, called asperities, prop them apart. That’s true even for apparently smooth surfaces like glass, which are still rough at the microscopic scale. It’s only the contacts between these asperities that cause friction. (via BBC – Future – Science & Environment – The power of science friction)

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s