The forward momentum of a bicycle without brakes can be interrupted by crashing it into an obstruction, a wall for instance, or a tree, or a parked car. A less embarrassing outcome can be achieved by applying friction between brake pad and rim, a little bit to slow down, a lot to stop abruptly.

Without friction, the bicycle cannot stop gracefully.

But the bike is aided by plenty of friction already, enabling the tire to stick to the road. The cyclist takes advantage of this to build momentum. Momentum drives the bike forward, faster and freer, in this case to an inevitable crash. Without this common friction, the bicycle just spins its wheels, or falls on its side.

Friction is a force at play at the interface of two surfaces. One surface is heading in a certain direction, the other is heading elsewhere (or is standing still). A match drawn across a flint encounters constructive friction. Deep in the earth's crust tremendous friction prevents one tectonic plate from sliding along another. When they finally do, the energy released shakes the earth.

The same can be seen within a family. A young girl becomes a young woman and wants to go out into the world, yet for her there may be no precedent for it. Her family might simply be standing still, and will cheer as she gains momentum and takes flight. Or she may find that it is much harder to break away. Rough going. Tough sledding. Is this friction? It is more likely resistance, or overt obstruction, but we sometimes describe it as 'friction'.

We find examples of friction within a community when one faction, or one member within a faction, rubs another the wrong way. Friction can occur between (the ruling classes of) two sovereign states, even when they do not share a border.

With friction one can hug the road, come to a full stop, spark a flame, fuel resentment, provoke an argument, engender ambition, find a solution or stoke a war. Maybe we should be talking about intent.

Read more about friction here.

Photo: Quino Al, Málaga, SPAIN @ Unsplash