# What is a good material for great traction but low friction?

caledon | Certified Educator

There's nothing that will provide both high traction and low friction under all circumstances, as the definition of traction incorporates friction and depends on it in order to function. We also can't discuss a single material in terms of its friction or traction properties because both of these depend upon the interaction between two materials, so we'd have to identify a pairing of whatever it is we're trying to move, and whatever it is it's moving on, such as rubber on concrete or iron on iron.

Friction is the force between two objects that resists their motion perpendicular to each other. Traction is the amount of force that can be generated in the perpendicular direction before the objects overcome their friction force and start to slip. Before this point, friction is determined by "dry friction." After this point, it's determined by kinetic friction.

These are the equations:

Dry friction force (traction) `<=` (coefficient of static friction) x (normal force)

Kinetic friction force = (coefficient of kinetic friction) x (normal force)

Basically, in the absence of friction, your traction would equal whatever force you applied in the forward direction. Add friction, and suddenly your traction force is reduced. You basically have zero traction until you can overcome the static friction holding you back in the first place. The moment you start moving, you've identified your traction force. After that point, any additional force you spend is used to add to your speed by overcoming the resistance from kinetic friction, since you've already overcome the static friction.

You can't change the normal force (the weight of the moving object), but you can change the coefficients of friction between static and kinetic, depending on the intermolecular and intramolecular forces acting on them.

The only way you might be able to get something that has high traction but low friction is if you're talking about low kinetic friction. Most metal-on-metal pairings will have higher static and lower kinetic friction, as you can visualize with a train struggling to get moving but also struggling to stop due to low kinetic friction. Under these circumstances, we can't really say the train has high traction.