By Oleksandr Koliakin
Let's start off with a thought experiment. Imagine that you are observing a special pendulum swinging machine. It swings a pendulum, which is made out of a random material (you don't know what it is), and tells you it's momentum, but as soon as it does that, it blindfolds you. You are then asked to tell the viewers where the pendulum is, and it's current momentum. You probably won't be able to do it (unless you guess, which is really unlikely). The longer you wait, the more certain you can be of the position of the pendulum (because it would eventually slow down due to air resistance), but the less certain you can be of it's momentum (in this experiment, we will imagine that as soon as the pendulum has a certain momentum, the machine will swing it again, meaning that the momentum is never 0 so that you can't easily guess the momentum).
In this thought experiment, you probably realized that the more certain you are of the momentum of the pendulum, the less certain you are about the position of it, and vice versa. In quantum mechanics, you the more certain you are about the momentum of the particle, the less certain you are of it's position, and vice versa. This is known as the Heisenberg Uncertainty Principle, and it is an important part of quantum mechanics (the area of physics related to elementary/fundamental particles, which are particles smaller than atoms).
In the equation above, delta-x is the uncertainty in the position of the particle and delta-p is the uncertainty in the momentum of the particle. The h with a line crossing through it is equal to the Planck's constant divided by 2 pi.