One thing that stringed, wind, and percussion instruments have in common in regard to the sounds they produce is that
a. the frequency is always a direct result of adjusting the length of the instrument.
b. the instruments are struck by tools to produce vibrations and sounds.
c. the sound originates from a vibration.
d. all of the instruments can be easily adjusted to produce a tone with a certain definite pitch.

Waves are used in many practical applications to support work, entertainment, and health. one example is the use of ultrasound imaging to safely track the development of a growing fetus. what is a specific example of a practical application of waves in medicine, entertainment, safety, or other fields? provide a brief explanation of how the properties of waves are useful to that application.

The softest and hardest minerals are: softest hardest

Simon is writing a story about an astronaut whose spacecraft has been boarded by space pirates. the astronaut has her lucky penny in her hand behind her back as the space pirates break into the control room. she has just locked the controls so that the ship is accelerating in the direction of the control room’s ceiling. simon wants the astronaut to use the penny to hit a button on the control panel to turn off the lights and escape. the button is located a short distance behind and below the astronaut’s hands. how should simon use the theory of relativity to describe what the astronaut must do in order to hit the button?