Page may contain affiliate links. Please see terms for details.
vickster
Legendary Member
Yes that could have been a solution, but then the QRs would have been on opposite sides, an aesthetic no for me!
raleighnut
Legendary Member
Take the QR out and turn it round before re-inserting?
Yellow Saddle
Guru
It depends on what you mean by "chemistry" and I don't want to get into a semantic war on this. It won't be helpful.
The branch of science concerned with friction (there are of course overlaps) is physical chemistry and when it leans over to the engineering side, tribology. Very very simplistically, this differs from pure chemistry where molecules bond by sharing electrons. In physical chemistry we are concerned with the interaction of molecules at close quarters rather than chemical reactions and bonds. "Close quarters" being in the nanometer range.
At this level a very weak force, Van der Waals comes to play. This weak force is caused by a temporary polarity within a molecule that attracts another temporary polarity in another molecule.
I'll attempt with a (obviously silly) example. If you represent molecules with tennis balls and assume that inside the tennis ball there is a bunch of positive and negative charges floating around in a fluid, you can imagine that if you bring a "magnet" close to the tennis ball, the charged particles inside will polarise. In other words, more positive charges will move towards the magnet than negative charges and the charge balance within the ball changes. The charge becomes lopsided inside the ball but no charges escape the ball (as it does in chemical reactions). If you take the magnet away, the charges inside the ball normalise again. When you press two substances together so that close contact (5 or so nanometer distance between molecules) is made, then adjacent molecules from the two camps temporarily re-arrange themselves and attract each other.
That is friction. It is very easily destroyed by distance. All you have to do to release the two adhering/cohering objects is to increase the distance between them slightly. This is usually done in friction examples most people understand, by reducing the Normal Force (downforce, if you like) on the two objects.
Although Van der Waal's is a very weak force, it accumulates nicely to amplify. To amplify it (get more molecules to attract each other) you just have to press them together so that at the micro structure more molecules meet and greet.
Back to your steel blocks. Friction is the only force that resists the sliding of the two over each other. By generating enough Normal Force between the two, friction is powerful enough to weld the two blocks together (galling of bearings).
winjim
Smash the cistern
NO.
winjim
Smash the cistern
I mean I don't expect that VdW forces are the sole contributor to frictional forces in the case of a tyre gripping the road.
Smokin Joe
Legendary Member
Next week's hot topic:
Tea, does the milk go in the cup first or last?
And does it matter which way you stir?
Tea, does the milk go in the cup first or last?
And does it matter which way you stir?
Alan O
Über Member
It depends on which end you eat your boiled egg from.
Dirk
If 6 Was 9
Milk?!
Racing roadkill
Guru
Now I've put the trolls back in the box, lets see if anyone who actually has a clue wants to contribute.
Racing roadkill
Guru
Possibly, but it would require something else to be there as well, bi metallics can react, and similar metals can react in the presence of a suitable antagonist, but your scenario is most likely to be purely mechanical in nature.
Racing roadkill
Guru
Or indeed, 'how do you peel your banana'
