Among the “eternal” topics of the school curriculum in physics, the “vibrations” section is perhaps the most nostalgic - it is always remembered with some kind of warm sadness. It is unlikely that at least someone recalling this topic does not see, first of all, tick-tock, tick-tock ... the pendulum is the “most serious” device from the physics cabinet. True, laboratory pendulums do not "tick", but with their classic medieval look they always say, swaying, their eternal tick-to-tick, tick-to-te ... "don't think about seconds down." And the task of these simple-looking devices is to clearly demonstrate what it is - oscillations.
We learn the world and see how much such a simple and uncomplicated action means around us. Oscillation is the Foucault pendulum, and the clock, and electricity, radio, TV, sound from the speaker, and your favorite cell phone is a whole bunch of oscillatory systems. Well, well, let’s remember what was taught at school - the amplitude of vibrations, formulas, graphics. So hesitation ... and what is it?
All that surrounds us is the "material points", which, for some reason, can not sit still. In this chaos of the variety of movements, oscillations are called the process in which the material point, sometimes the system says, always returns to the equilibrium position if it deviates from it many times. In this case, the maximum deviation from the equilibrium point is called the amplitude of the oscillations. The best device for demonstrating mechanical vibrations, of course, is an old, good pendulum - a load (ball, disk or rod) suspended on a thread. Fix it motionless - and here is a state of equilibrium. Take the load aside and let go, what do you see? That's right, he will start his “tick-tock”: he will return to the equilibrium position, deviate to the other side, then again return to the equilibrium position. If nothing prevents the pendulum, then it, restless, will again deviate to the side ... and so on continuously, until, due to the friction force, it still stops.
It just so happened that any object that has mass, size and other distinctive signs necessarily contains a set of characteristics that can uniquely describe this “material point” so that its behavior from interaction with the environment is predictable, logical and understandable. Such characteristics of the pendulum are the amplitude of the oscillations and the period. Other commonly used parameters are derivatives of the original ones, they are their organic part (phase) or the result of additional calculations (frequency).
The next step in studying the fascinating world of oscillations is the simplest experiment to determine the parameters of our object - the pendulum. The device of the pendulum is nowhere easier - a thread, a ball, a suspension point. But how to find the amplitude of oscillations of such a pendulum? Yes, it is so simple that such an experience, as they say, can be done in the kitchen. Everything is easy (within certain limits). Initial task: there is a pendulum suspended from the ceiling - a metal disk on a thread. We are interested in the magnitude of the deviation of the disk from the equilibrium position. With a fixed pendulum, make a mark on the equilibrium point on the wall, or on a paper screen mounted at the back. Push the disk. The pendulum will begin to oscillate, and the shadow of the disk will “draw” the trajectory on the screen. Moving the stick (you can use a pencil) on the screen, we find the last point, when the shadow, when fluctuating at the extreme point, closes our pointer, and make a mark. The distance from the equilibrium point to the mark will be the amplitude of the oscillations of the pendulum. Really easy? And who would doubt it.
Of course, it is possible to “modernize” the experiment with electronic bells and whistles with photo sensors or use laser distance meters, measure it up to some attractive digits after the decimal point, but nothing can change its essence - the largest deviation of the pendulum from the equilibrium position has been measured, i.e. the amplitude is measured. In our experiment, it is easy to find one “secret” of the pendulum - its amplitude of oscillations depends only on the initial conditions, i.e. in fact, from the strength of the first shock that violated the state of equilibrium, or the initial energy imparted to the oscillatory system, when the pendulum is deflected at some angle from the equilibrium position.