Forces in mechanics most often manifest themselves in such a subsection as dynamics. It is there that the motion of bodies is studied taking into account the forces acting on them. We will talk about what forces in mechanics are, what nature they are and how they can be calculated.
What is the basis of dynamics
As mentioned earlier, forces in mechanics manifest themselves most often in this subsection. And if so, then it will not be superfluous to know what the theoretical basic existence of dynamics is in general. Perhaps, someone already guessed that we are talking about the famous Isaac Newton, and more precisely, about the laws deduced by him. The unit of force in mechanics, by the way, is precisely why it bears his last name.
What do Newton's laws allow you to do?
They allow us to solve the main problem in the event that all the forces acting at a given time on the body under study are known for certain. Suppose this is true, and we know them. Then, without much difficulty, one can find acceleration applicable to the body. But knowing what acceleration is in modulus and direction will open up to us the prospects of searching for the speed of the body at any desired time. As a result, we can determine the position of the material point when we want. Here we can emphasize the importance of the inverse problem. It turns out that to solve problems, you should initially correctly place the forces in mechanics, the formulas of which will be given below.
Nature of forces
If we open a textbook, a physics problem book, or other reference material and turn to the section on mechanics, we will see many problems from dynamics, where most often we encounter only three forces. They are related to universal gravity, friction and elasticity. Let's talk about each of them in more detail. And let's start with the first one.
The body falls from a height without initial velocity
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 air resistance, although this approach is not always reasonable. But what do we get? Then it turns out that all bodies have approximately the same acceleration during free fall. Whether we throw a small pebble or real cobblestone down, the speed and time of the fall will be approximately the same.
Add a spring to the system
Imagine that a weight was suspended from a spring. He, like any other body, will tend to fall to the ground. At this time, the force of gravity of our planet acts on it. However, if the spring is strong, then it will stretch to a certain point. After this, the fall of the body will stop, and the system will come into a state of so-called mechanical equilibrium. It takes place when several forces act on the body, but their sum is zero. In other words, the actions of the forces are compensated.
Here a logical conclusion begins to beg. It turns out that in addition to gravity , another weight is acting on the weight from the side of the spring, numerically equal to attraction. It has a very simple name given by the phenomenon. They call it 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 that. But if you dig deeper, the case will take a rather interesting turn. There is a wonderful Newton's law (second), which states that force is equal to the product of mass and acceleration communicated to the body. At first it may seem (exclusively mathematically) that strength is a result. But no, in fact the opposite is true.
Imagine a soccer ball being hit. He is informed of the force, after which he acquires a certain acceleration. Similarly, in the case of body movement. It, having passed this or that distance, will stop. Acceleration will have a negative value until the speed is equal to zero. We can immediately put forward the assumption that there is a certain force that slows down the body, that is, is the cause of this very negative acceleration. And she really exists. This is the force of friction.
Moment of power. Mechanics: theoretical and technical
The moment of force will be called the rotational force created by the rotation of the force vector relative to the implied point or body. It has a dimension of Newton per meter. The conditions of occurrence are quite simple. For this, it is enough that the point does not lie on the line of action of the force. The moment can be defined as the product of strength and shoulder. The simplest example would be to tighten the nut with a wrench. The force in theoretical mechanics is almost no different from the analogues in the classical section, so there is no point in delving into it for a more detailed consideration. Back to the basics, because they are much more important.
Again about the force of elasticity
The reader can always personally verify what will be said now. Suppose we have a solid. Any solid body is resisting when trying to change shape, size. But these operations are nothing but ordinary deformation, right? But what are its types? There are five main types of deformation: tension, compression, bending, torsion, shear.
What will happen when I 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 bring them back. In the event that the deformation is small compared to the original dimensions, the elastic forces can do this. Another thing, if everything is exactly the opposite. But the study of such processes has already been done by 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 he began to stretch. In this case, elastic force arose, as you might guess, inside the rod itself. It was measured in the process of stretching. To describe the processes in quantitative terms, introduced a new value, subsequently called elongation. This is nothing more 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, there is a direct proportion between elongation and elastic force. Here another quantity takes place, which we call the coefficient of elasticity. It depends on what material the body is made of, as well as on what linear dimensions it has.