Beats.
When two sound waves of different frequency approach your ear, the alternating constructive and destructive interference causes the sound to be alternatively soft and loud - a phenomenon which is called "beating" or producing beats. The beat frequency is equal to the absolute value of the difference in frequency of the two waves.
Dependent on what you are measuring and what took you are using. Please be more specific.
B. Flipped compared to what is in the sky
<span>A wedge is a double sided screw basically. Therefore, the difference is the number of sides.</span>
The first law is about force or push and pull
