Forces in mechanics. Unit of force in mechanics

Forces in mechanics most often manifest themselves in such a subsection as dynamics. It is there that the movement of bodies is studied taking into account the forces acting on them. About what the forces in mechanics are, what kind of nature they have and how they can be calculated, we will talk today.

What is the basis of dynamics

As it was said before, the forces in mechanics manifest themselves most often precisely in this subsection. And if so, then it will not be superfluous to know what in general is the theoretical basic existence of dynamics. Perhaps someone already guessed that we are talking about the famous Isaac Newton, or rather, the laws he derived. The unit of force in mechanics, by the way, is precisely why it bears his name.

What do Newton's laws allow?

They allow us to solve the main problem in the event that all the forces acting at a given instant of time on the body under investigation are known for certain. Let us assume that this is indeed so, and we know them. Then without much difficulty you can find the acceleration applicable to the body. But the knowledge of what modulus and direction is acceleration, will open up before us the prospect of finding the speed of the body at any given time. As a result, we can determine the position of the material point when we want. Here it is possible to emphasize the importance and the inverse problem. It turns out that to solve problems initially it is necessary to place correctly the forces in mechanics, the formulas of which will be given below.

Nature of strength

If we open a textbook, physics handbook or other reference material and turn to the mechanics section, we will see a lot of problems from the dynamics, where we most often encounter only three forces. They are related to universal gravitation, friction and elasticity. Let's talk about each of them in more detail. And start, perhaps, with the first.

The body falls from a height without having an initial speed

Such cases are called free fall. Everything that surrounds us is attracted to our planet. Including ourselves. Here, a similar fact can be determined by the forces of universal gravitation. Now we can neglect the resistance of air, although this approach is not always reasonable. But what do we get? Then it will come out that all bodies have about the same acceleration at free fall. Whether we throw a small pebble or a real cobblestone down - the speed and time of the fall will be approximately the same.

Add to the system a spring

Imagine that a spring was suspended on the spring. He, like any other body, will strive to fall to the ground. At this time, the force of attraction of our planet acts on it. However, if the spring is strong, it will stretch to a certain point. After this, the fall of the body will stop, and the system will come to a state of so-called mechanical equilibrium. It occurs when several forces act on the body, but their sum is zero. In other words, the actions of the forces are compensated.

Here comes the logical conclusion. It turns out that, in addition to gravity , another force acts on the weights on the spring side, numerically equal to the attraction. It has a very simple name, given by the phenomenon. They call it the force of elasticity. The unit of force in mechanics is universal, and here it is also equal to one Newton.

Is acceleration the reason for the change in speed?

Maybe. At first glance, everything looks like this. But if you dig deeper, the matter will take a rather interesting turn. There is a remarkable law of Newton (the second), which says that the force is equal to the product of the mass for acceleration, reported to the body. At first it may seem (exclusively mathematically) that power is the result. But no, in fact, the opposite is true.

Imagine a soccer ball that is beaten. He is given power, after which he acquires a certain acceleration. Similarly, in the case of body movement. After passing this or that distance, it will stop. Acceleration will have a negative value until the speed equals zero. We can immediately put forward the assumption that here there is a certain force that slows down the body, that is, it is the cause of this most negative acceleration. And it does exist. This is the force of friction.

Moment of power. Mechanics: theoretical and technical

The moment of force will be called the rotational force created as a result of the rotation of the force vector with respect to the implied point or body. It has the dimension of Newton per meter. The conditions of origin are quite simple. To do this, it is sufficient that the point does not lie on the line of action of the force. You can determine the moment as a product of strength and shoulder. The simplest example is the tightening of the nut with a key. The strength in theoretical mechanics is almost no different from the analogs in the classical section, so there is no point in going into it for more detailed consideration. Let's return to the basics, because they are much more important.

Again about the strength of elasticity

The reader can always personally verify what will be said now. Suppose we have a solid body. Any solid body exerts resistance when trying to change shape, size. But these operations are nothing more than an ordinary deformation, right? But what are its types? There are five basic types of deformation: stretching, compression, bending, torsion, shear.

What will happen when you try to change the shape and size?

It already depends on the nature of the body. In general, deformation is elastic and not elastic. But you should know that in any attempt to change the shape and size of the body, it will try to return them back. In the event that the deformation is small in comparison with the original dimensions, the elastic forces will be able to do this. It's another matter if everything is exactly the opposite. But the study of similar processes was already being done by the scientist Robert Hooke. His experiments, which gave wide coverage of the process of deformation in bodies, he conducted in 1660.

What did this scientist do?

He took a solid rod, which began to stretch. At the same time, as you might guess, there was a force of elasticity inside the rod itself. It was measured during the stretching process. To describe the processes in quantitative terms, introduced a new value, later called an extension. This is none other than the difference in the linear dimensions of the body in the ordinary and extended states. The results of the experiment even surprised some. As it turned out, in the case of small deformations between elongation and the elastic force, there is a directly proportional relationship. Here we have another quantity, which we call the elasticity coefficient. It depends on what material is made of the body, and also on what linear dimensions it has.