The Natural Philosopher wrote:
Grimly Curmudgeon wrote:
On Sun, 09 Sep 2012 17:34:49 +0100, The Natural Philosopher
wrote:

but if it wasn't for friction, the wheels would simply spin on the
ground.

that's not what slows you down. Friction between surfaces that are
not moving relative to one another wastes no power.

But they are moving relative to one another, all the time.

not at the pint of contact. That's the whole point

Unless you are in a wheelspin mode

hardly likely if you are towing or pushing a van.


Look closely at the part of a tyre which is in contact with the ground,
and you will see that due to the way the rolling radius varies along the
flat part, there must always be a small amount of slippage between the
tyre and the ground which may or may not be absorbed by the elasticity
of the tyre material. This applies to all wheel/ ground interactions
where the wheel and ground are not perfectly rigid.

Incidentally, in the 19th Century, experiments were done which gave the
hauling capacity of a horse at walking speed on a level surface as
(roughly) 4 tons on a metal tyred, thin wheeled cart on a good hard road
surface, 7 tons on a railway waggon and 10 tons on a narrowboat. The
road figures may have changed slightly when the pneumatic tyre was
invented and came into use.

--
Tciao for Now!

John.