Any movement in nature and technology, which involves the presence of physical contact between solid bodies, is accompanied by friction. In this article, we will give examples of the friction force and show in which cases it plays a useful role, and in which it is undesirable.
What types of friction between solids are
In this article, we will consider only examples of frictional forces that act between solid objects that have physical contact with each other.
One of the important types of friction is static friction. Based on the name itself, it can be assumed that it manifests itself when one body rests on the surface of another. Everyone knows that in order to move some heavy object from its place, it is necessary to apply some external force directed along the contact surface of this object and the surface on which it stands. This force is counteracted by the static friction force. It acts between the contact surfaces of bodies. Friction of rest arises due to the presence of roughness on the touching surfaces, no matter howthey were not smooth.
The second type of friction we'll look at is sliding friction. It also arises due to the mentioned roughness, when the bodies begin to move relative to each other by sliding. The direction and point of application of the sliding friction force are exactly the same as for static friction. The only difference between these forces is that the sliding force is always less than the resting force.
The third type of friction, which plays no lesser role in technology than the first two, is rolling friction. As its name says, it appears when one body rolls on the surface of another. The reason for rolling friction lies in the hysteresis of deformation, which leads to the "dispersal" of the kinetic energy of the rolling body. In a number of practical cases, this friction force is 10-100 or more times less than the previous types of friction considered.
All types of friction forces are directly proportional to the support reaction force with which the latter acts on the body in question.
Harm and benefit of static friction force: examples
Of all the named types of friction, perhaps, static friction is the most "harmless". The fact is that in practice it almost always plays a useful role. Its only negative point is that it is greater than sliding friction. The latter fact means that for any start of movement it is necessary to apply a great effort. For example, to start skiing on snow, you first need to literally "tear" them off the snow surface.
There are many examplesuse of static friction force. Let's list them:
- Nails and screws that firmly hold two solid bodies of wood, plastic and metal together perform their function through the action of the force in question.
- Walking a person, driving cars on the roads is due to the fact that the static friction is greater than the sliding friction. Otherwise, it would be difficult for us to move, people and vehicles would slide in one place.
- Any bodies that rest on inclined surfaces are due to the action of static friction. If the latter did not exist, then it would be impossible to put a handbrake on a car on a slope or any household item on a table that has a slight inclination to the horizon.
Sliding friction and its benefits
Unlike static friction, which mainly plays a positive role in human life, sliding friction is usually a harmful force. However, two examples of useful sliding friction force can be given:
- Since sliding friction leads to heating of the surface of objects (the natural and easiest way to convert mechanical energy into heat), this effect can be used to increase the temperature of bodies. So, in ancient times, our ancestors made fire using sliding friction.
- When the driver wants to stop the vehicle, he presses the brake pedal. In this case, the brake discs slide inside the wheel rim and slow down its rotation.
Harm sliding friction
Examples of the action of sliding friction are the movement of a cabinet on the floor when we want to rearrange it in a room, the sliding of a skier and a skater, the slippage of a car's wheels when they are blocked or when driving on a slippery road, slippage between the rubbing parts of the mechanisms of various machines.
In all these cases, sliding friction plays a harmful role. These examples of the harm of sliding friction are due to the fact that it prevents mechanical movement and "eats" a certain amount of kinetic energy (skis, skates, moving parts of machines). In addition, the transfer of part of the mechanical energy into thermal energy leads to heating of the rubbing parts. An increase in their temperature leads to a change in the microscopic structure, which violates the properties of materials. Finally, the listed examples of the sliding friction force lead to wear of the rubbing surfaces, the appearance of unwanted grooves on them, and thinning.
Rolling friction and its harm and benefit
If we consider fundamentally the question of the usefulness of the rolling friction force, it turns out that it does not exist at all. Indeed, rolling friction always prevents mechanical rotation, it leads to wear of working parts and to their undesirable heating. Nevertheless, the rolling phenomenon is widely used in engineering (bearings, vehicle wheels). This is explained by the fact that the rolling friction force is much less than the similar sliding force, which reduces its scale by orders of magnitude.harmful influence.
Increase and decrease in friction forces
As we saw above in the examples, the static and sliding friction forces are sometimes useful and sometimes harmful. In this regard, since ancient times, humanity has been using methods to change the scale of friction, both in the direction of increasing the corresponding force, and in the direction of decreasing it.
Great examples of how to increase the force of friction are the sprinkling of sand and s alt on the ice on the roads. As a result of these actions, there is an increase in the roughness of the ice surface and, as a result, an increase in the forces of static and sliding friction.
Another way to increase the forces in question is to use special surfaces. A striking example is the surface of a car's winter tire, which is characterized by a deep tread and the presence of metal spikes.
During skiing, as well as during the rotation of bearings of various mechanisms, friction plays a negative role. To reduce it, special lubricants are used, usually based on fats (wax, lithol).
