Importance of frictional forces

Question: Friction is often regarded as a nuisance. State two different situations where friction is of critical importance.

1. While a car is moving at high speed, there must be sufficient frictional force between tyres and a road surface such that we can increase or decrease the speed of the car. If there is no kinetic frictional force between the tyres and the road surface, we cannot even accelerate or decelerate the car.
2. The floors in a building should have sufficient frictional force such that we do not slip and fall. There are fatal accidents such as elderly slips and falls in a bathroom. (Similarly, when we place objects such as glass bottles on a table, it is the static frictional force that keeps the glass bottles at rest. If there is no static frictional force, a gentle breeze can cause the glass bottles or any objects to slide and fall onto the ground.)

 

Question: For one of your examples explain why friction is so important.

The need of sufficient frictional force between the car’s tyres and road surface is extremely important for road safety. When the coefficient of friction between the tyres and the road surface is relatively low, we will have difficulties to decelerate and stop the car within a short period of time, and this can result in traffic accidents. That is why traffic accidents happen more frequently because of rains or snows.

 

Further details: There is a close correlation between the frictional force of road surface and risks of traffic accidents. For instance, worn tyres are likely to contribute towards traffic accidents in wet conditions of roads as compared to dry conditions. For a discussion of frictional force of bathroom, you can visit the following website:

 

Note:

Feynman has a good explanation of frictional force: “We have just discussed two cases of friction, resulting from fast movement in air and slow movement in honey. There is another kind of friction, called dry friction or sliding friction, which occurs when one solid body slides on another. In this case, a force is needed to maintain motion. This is called a frictional force, and its origin, also, is a very complicated matter. Both surfaces of contact are irregular, on an atomic level. There are many points of contact where the atoms seem to cling together, and then, as the sliding body is pulled along, the atoms snap apart and vibration ensues; something like that has to happen. Formerly the mechanism of this friction was thought to be very simple, that the surfaces were merely full of irregularities and the friction originated in lifting the slider over the bumps; but this cannot be, for there is no loss of energy in that process, whereas power is in fact consumed. The mechanism of power loss is that as the slider snaps over the bumps, the bumps deform and then generate waves and atomic motions and, after a while, heat, in the two bodies. Now it is very remarkable that again, empirically, this friction can be described approximately by a simple law. This law is that the force needed to overcome friction and to drag one object over another depends upon the normal force (i.e., perpendicular to the surface) between the two surfaces that are in contact. Actually, to a fairly good approximation, the frictional force is proportional to this normal force, and has a more or less constant coefficient; that is, F = μN, where μ is called the coefficient of friction (Feynman et al., 1963, section 12-2 Friction).”

Reference:

Feynman, R. P., Leighton, R. B., & Sands, M. (1963). The Feynman Lectures on Physics, Vol I: Mainly mechanics, radiation, and heat. Reading, MA: Addison-Wesley.