explain why a solution of a strong acid has a different ph than a solution of a weak acid of the same concentration?

A strong acid is an acid which completely ionizes in water to give hydrogen ions (hydronium ions).
A weak acid is an acid which only partly ionizes in water to give hydrogen ions.

Because the strong acid has a higher degree of ionization than the weak acid, the strong acid ionizes to give a higher concentration of hydrogen ions, [H⁺], than the weak acid.

pH = -log[H⁺]
As the strong acid and the weak acid produce different concentrations of hydrogen ions, [H⁺], they have different pH.

It's because the equilibrium constants are very different. It's all about the percentage on dissolved ions.

Don't confuse the words strong and weak with the terms concentrated and dilute; the strength of an acid is related to the proportion of it which has reacted with water to produce ions. The concentration tells you about how much of the original acid is dissolved in the solution.

Strong acid or base means it ionizes completely in water. It has nothing to do with concentration or corrosiveness. There are seven strong acids:

Sulfuric
Nitric
Hydrochloric
Chloric
Perchloric
Hydrobromic
Hydroiodic

It's easy to remember the list because there are three of the most common industrial acids, three "chloric" acids, three "hydro" acids, and they all make a clumsy "7" on the periodic table.

There are dozens of strong bases and hundreds of "almost strong" bases.