becuase they are silent
Some examples of English words with a silent P are pneumonia, pneumatic, psychic and psychiatrist.
pneumoniapsalmpseudonympsychiatricpsychiatristpsychicpsychologyptomaineptarmiganpsychpsychepsychopsychopath
(*excluding the words that begin with PH and have an F sound : pharmacy, phenol, photo) There is a silent P in pneumonia, ptomaine, pteradactyl, raspberry, receipt, and PS words such as psalm, psychology, and pseudonym.
The word rendezvous is the only word in the English Dictionary that has a silent z. It is pronouced, [rahn-duh-voo].
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 3 words with the pattern P-EUM----. That is, nine letter words with 1st letter P and 3rd letter E and 4th letter U and 5th letter M. In alphabetical order, they are: pneumatic pneumonia pneumonic
The silent letter in "pneumatic" is the "p." It is not pronounced in the word.
pneumatic
p u
Panther, piranha, pirates, plague, pneumonia, polar bear, porcupine, prison and python are scary. They begin with P.
In the word "psychology," the "P" is silent because it is derived from the Greek word "psyche." The English language borrowed this word along with its silent "P." In words like "pneumonia" or "psychiatry," the "P" is silent as well, following the same etymological pattern.
Pneumonia.
A current signal can be converted into a pneumatic signal using a current-to-pressure (I/P) transducer. The transducer converts the electrical current input into a corresponding pneumatic pressure output that can be used to operate pneumatic devices like cylinders and valves. This conversion allows for the control and automation of pneumatic systems using electrical signals.