Why do some symbols have a capital letter and a lower-case letter?

In scientific notation, the use of capital and lowercase letters in symbols often denotes different meanings or units. For example, in physics, "v" might represent velocity, while "V" refers to voltage. This distinction helps to clarify the context and ensures precise communication in scientific writing. Additionally, capital letters may represent specific constants or quantities, such as "G" for the gravitational constant, while lowercase letters are used for variables or measurements.