BASIC UNITS

The units which we use are in A Level physics all come from the SI (Systeme International) system. They provide a standard to which almost everyone adheres. All units in the SI system are derived from the 7 basic units listed below

The dimensions of a quantity are the powers to which the fundamental quantitys are raised in it. The 3 most common dimensions are often abbreviatted to [M] mass, [L] length , [T] time. Thus ,for example, Force which is equal to mass * acceleration will have the units of kg m s^-2 and so dimensions of 1 in mass, 1 in length and -2 in time, could be written as [M]¹ [L]¹[T]^-2.

• Dimensions in equations must be equal on either side.
• Just becasue dimensions are equal does not prove an equation correct.
• Units normally have a lower case symbols, unless they are named after a person.