After the Civil War , with the protection of the Thirteenth , Fourteenth , and Fifteenth Amendments to the Constitution and the Civil Rights Act of 1866 , African Americans enjoyed a period when they were allowed to vote , actively participate in the political process , acquire the land of former owners , seek their own employment , and use public ...
In the knee, for example, cracking or popping may occur if the patella (knee cap) is slightly out of alignment, and rubs on the adjacent tissues. Other causes of joint noise are the snapping of tendons or scar tissue over a prominence or something referred to as cavitation. Cavitation frequently occurs in synovial joints when a small vacuum forms in the synovial fluid and a rapid release produces a sharp popping or cracking sound.
So, why do your ears pop and why does your stomach drop when you're on an airplane? Your ears pop in airplanes because the air high above the surface of Earth is less dense than air near the surface, because air near the surface has all the air above it pushing down. Your inner ear has air trapped in it and as the atmospheric pressure changes, it causes pressure on your ear drum.