The reader may... wonder why when amber is rubbed with fur the electrons go from the fur to the amber, but when glass is rubbed with silk the electro… - Steven Weinberg

The s and s in nuclei, like the electrons surrounding the nuclei, can be excited to states of higher energy or... fall back to a state of lower energy, but the energies... are typically a million times those need to excite the electrons...

The laws of motion... were set out by... Newton at the beginning of... the Principia. ...[T]he key principle is ...in the Second Law... paraphrased as... the force to give an object a certain acceleration is proportional to the product of the and the .

One of the things that excited me so much about quantum chromodynamics after the work of Gross and Wilczek and Politzer was that it seemed to provide a rational explanation for what had always been mysterious to me — the fact that there were symmetries, like parity conservation, charge conjugation invariance, and strangeness conservation, that were very good symmetries of the strong and electromagnetic interactions — as far as we knew exact — and yet were not respected by the weak interactions. Why should nature have ... symmetries that are symmetries of part of nature but not other parts of nature?