Where the different rules of physics apply:
Regular, otherwise known as Newtonian physics only applies on the average, everyday, scale. That is, objects larger than an atom at low energy, where energy in this context refers to velocity and (sometimes) temperature.
Once you step it up, increasing to high energy levels, (when velocity approaches c, the speed of light) newtonian physics no longer works due do what we call relativity, and observations or calculations need to take into account this effect usually using some form of the Lorentz factor,
gamma = [ 1 - (v^2)/(c^2) ]^(-1/2)
On the other hand, if you keep to a low energy system but bring the scale down to sub-atomic particles, such as electrons, things change yet again, but this time in an entirely new way. This is where Wave-Particle dualtity theory comes into play, the theory that waves (namely electromagnetic, i.e. light) are particles, and particles are wave packets. not only do you need to account for this, but you also need to take into account Heisenbergs uncertainty principle; It is impossible to know both the exact velocity and exact position of a sub atomic particle, the more certain you make one the less certain the other becomes.
Finally we come to Quantum Field Theory, which i honestly do not know anything about, at least i won’t until third year physics when i start taking courses on it.