How do analog and digital signals work in the context of physics or electricity?

Traditionally, internet is accessible to every home via the normal telephone lines connected. The data transmitted from the telecommunication company (also ISP) to a DSL modem inside each home is in form of analog (voice) signal. Then, the modem converts the analog signal to digital signal and sends it to a connected computer.

The digital signal is represented by the number zero (0) and one (1). But physically, it's a voltage pulse. For example, if the modem detects the voltage pulse from within the cable greater than zero, it interprets as 1; otherwise, it interprets as 0.

The analog signal is pictured as a wave signal. But physically, it's just a series of voltage pulses within a timeframe. The voltage generated within the cable continuously rises and drops again and again within a time interval so that the signal receiving device can conceptually interpret it as wave frequency.

Reference:

https://www.computernetworkingnotes.com/networking-tutorials/how-analog-and-digital-signals-work.html

Basic Physics Terminology

Atom

It comes from the Greek word "Atomos". "A" means not and "tomos" means cut so atom means indivisible (unable to be divided). It's the basic building block of a matter. Atoms can join together to form a molecule.

Electric charge 

It can be negative (electron) or positive (proton). While opposite charges attract each other, the same charges repel each other.

Particle

A particle is the small piece of anything (from vocabulary.com). For example, oxygen and hydrogen are particles. A molecule can also be referred to as a particle. An atom is made up of three (sub) particles: neutron, proton, and electron.

Molecule

It's a particle made up of two or more atoms that are chemically bonded together. The number of atoms within a molecule is a determined number, and it identifies the particle. For example, a water molecule consists of two atoms of hydrogen linked by covalent bond to the same atom of oxygen.