Principle 7. "Nested doll"

1. Place one object inside another; place each object, in turn, inside the other.
   
   • Measuring cups or spoons
     
   • Russian dolls
     
   • Portable audio system (microphone fits inside transmitter, which fits inside amplifier case)
     
2. Make one part pass through a cavity in the other.
   
   • Extending radio antenna
     
   • Extending pointer
     
   • Zoom lens
     
   • Seat belt retraction mechanism
     
   • Retractable aircraft landing gear stow inside the fuselage (also demonstrates Principle 15, Dynamism).