The world around us is a world of movement in which no body is in a state of absolute rest. At the same time, uneven motion would be impossible if the so-called friction force did not exist. In this article we give examples of the manifestation of friction in nature and in technology.
What is friction in physics ?
Before considering examples of friction in nature and in technology, you should understand? what constitutes this power.
In physics, friction is understood to mean any force interaction that interferes with mechanical motion and appears in the contact region of two bodies. The friction force is the contact force of interaction, and the aggregate state of the contacting materials does not matter in terms of the existence of this force.
In the general case, four types of friction are distinguished . The first three of them relate to the contact of a solid with a solid. These are the following types:
- friction of rest;
- sliding friction;
- rolling friction.
The fourth type of friction has no special name. It manifests itself when bodies move in fluid substances, that is, in gases and liquids.
Friction of rest and examples of its action
We begin the disclosure of the issue of friction in technology and in nature with examples of manifestations of static friction. This type of friction acts between any solid body and the surface on which it rests. The rest friction force is directly proportional to the reaction of the support N, with which the surface acts on the body. The corresponding formula for its calculation is:
F t = μ t × N,
where µ t is a coefficient that is measured experimentally and depends on the material of the interacting bodies.
Each of us noticed: in order to move any object, it is necessary to apply some force. For example, move the cabinet or push the machine from its place. The difficulty in performing these manipulations is connected with the action of rest friction against the external force directed by a person.
The importance of resting friction is enormous. So, thanks to this force, objects do not fall from shelves and tables, which are slightly inclined to the horizon. Thanks to static friction , the movement of people and vehicles is possible. For example, when the sole of our foot is pushed off the floor to give the body an impulse directed forward, then the absence of slipping of the sole on the floor is provided by rest friction.
Sliding friction and examples of its manifestation
Continuing the consideration of the friction force in nature and in technology, we turn to sliding friction. By it is meant the existence of a contact force that impedes the sliding motion of one solid on the surface of another. The formula for determining this force has exactly the same form as for rest friction, so we will not give it here. Nevertheless, we note that the sliding friction coefficient µ t is always several tens of percent less than the similar coefficient for rest friction. The latter means that the force that prevents slipping is always less than that which prevents the start of movement.
Vivid examples in the technique of sliding friction are skating and skiing. In both cases, they seek to reduce the considered frictional force so that gliding occurs with the least energy loss. So, in the case of skis, a special wax-based lubricant is used. It makes the surface of the skis less rough, which helps reduce friction. In the case of skates, it should be noted that in the area of contact between steel and ice, ice melts as a result of tremendous pressure. The resulting thin water layer significantly reduces the coefficient of friction between the steel ridge and ice.
An example in nature of sliding friction is the following: in winter, you can often see that the streets in cities are sprinkled with salt and sand. This is done in order to increase the friction force of rest and sliding, which prevents pedestrian injuries from falling on a slippery surface and reduces the number of car accidents on the roads.
Rolling friction in technology
The invention of the wheel was a giant step forward in the development of mankind. This is made possible by rolling friction. The formula for its calculation is identical to the expressions for the types of friction described above. Nevertheless, this force has a completely different nature. It is associated not with surface roughness, but with the deformation of a rolling body, such as a wheel.
An important difference between the rolling friction forces and the rest and sliding friction forces is that in many cases it is 10-100 times smaller. That is why cars are able to move on roads with great speed and low energy costs.
Another example in the rolling friction force technique is the rotation of bearings around respective metal axes. Lubricants are also used in bearings to reduce rolling and sliding friction. Note that the invention of the bearing is no less important than the invention of the wheel itself. Thanks to bearings, all types of rotational movement of various mechanisms (blades, pedals, wheels) are carried out.
Friction in fluid substances
This friction always appears when a solid moves in a volume of gas or liquid. Examples in the technique and nature of friction in gases are flights of airplanes and birds.
In liquids, friction acts on the inhabitants of the seas and oceans when they swim under water. The pointed form of fish, as well as submarines and ships, is designed to reduce the frictional force when moving in water.
The action of various types of friction on the example of car movement
A number of examples of friction forces in technology and in nature were given above. In reality, when an object moves, several types of friction forces act on it simultaneously. For example, to start moving, a car must overcome the frictional force of rest. As soon as he does this, then in the process of moving along the road, rolling friction will begin to act on him. When turning or braking the car, the wheels partially slip on the asphalt, i.e. sliding friction appears. Finally, when driving, a car overcomes not only rolling friction, but also friction associated with exposure to air.