You're just like those people who clap at the end of movies. If you feel the need to applaud a lot - go down to your local jazz club. And the live performers CAN hear you. And they like to hear clapping. An orchestra is a group of musicians - frequently in tuxes and black dresses who play a variety of instruments.
All orchestras have string sections.
It is a rule. Later, as more musicians became available, more were added. Mozart and Haydn added trumpets, drums, flutes, and more. Then Beethoven came along and added a whole load of new people - musicians and also singers. Mozart had somewhere around 40 people in his orchestras.