A periodontist is a dentist who specializes in the prevention, diagnosis, and treatment of periodontal disease, and in the placement of dental implants. Periodontists are also experts in the treatment of oral inflammation.
Ground speed. Ground speed is the horizontal speed of an aircraft relative to the ground. An aircraft heading vertically would have a ground speed of zero. Information displayed to passengers through the entertainment system often gives the aircraft ground speed rather than airspeed.
A 90 MPH fastball, the go-to pitch and speed for the top echelon of pitchers, is travelling at 132 feet per second. Since the ball is closer to the batter when it is released and because the batter is in the middle of the plate depth, we are really only talking about 55 feet to see a pitch rather than just over 60.