The vertical flight of a helicopter is controlled by

Archimedes’ principle states that

The main supporting members of a wing are

The elevators of a conventional airplane are used to provide rotation about the

If the pressure of a dry gas is reduced by one third, the volume will

An airplane wing is designed to produce lift resulting from relatively

An observer sees the flash of a gun three seconds before he hears the sound of the gun firing.  Approximately how far is the observer from the gun?   (speed of sound = 1100 ft/sec)

When a weight on a string is spun around and the string is released, the weight travels

The speed of sound

41) Sal’s dog Nymeria loves to see the mailperson because the mailperson always gives Nymeria a treat. The mailperson usually comes at around 1 PM, but sometimes comes as early as 11 AM and sometimes doesn’t come until 4 PM.  This is an example of what type of reinforcement schedule?