1. Mechanical phenomena

The large bodies surrounding us in physics are called macroscopic. Let's not specify at once how big a macroscopic body should be. Especially no exact border can be set anyway. It can be gas in a container, water in a glass, grain of sand, stone, piece of metal, globe, etc.

In the second book you learned about mechanical motion and Newton's laws. These laws allow us to calculate how macroscopic bodies or parts of them will move relative to each other. To do this, you have to know the initial positions, the initial velocities of the bodies and the forces of their interaction.

However, many questions are not answered by Newton's mechanic. Why, for example, the deformation produces elastic forces? Why bodies produce frictional forces when are moving in liquids and gases or slide over hard surfaces? Why does the water rises up in narrow tubes despite the force of gravity?

Newton himself understood it all well. He's got great words for it: "I do not know what I may appear to the world, but to myself I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me."

In mechanics, the difficulties associated with the determination the nature of forces and their origin are not significant, because to calculate the trajectories motion of bodies it is enough to know only what the forces are quantitatively equal. And to know the value of forces, to determine when and how they work, it is possible not to understand the nature of forces, but only by having ways of measuring them. It's all true. But if we want to know how the world around us works, we cannot abandoned the task of studying the nature of forces.

And it's not just about forces. It's not clear from mechanics, for example, why there are three types of bodies: gaseous, not retaining their volume; liquid, volume retaining, but not form retaining; and solid bodies which retain their form. Why gases turn into liquids and liquids into solid bodies when they are cooling.

Now our task will be to learn to answer many of these and similar questions. The first step to achieving this goal is to get to know a large group of new physical phenomena.