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.
When something is moving faster, it hits those more often, making it slow down even faster. Heavier objects are affected less by air resistance, which is why they fall faster on earth. All terminal velocity is is the fastest speed an object can go before the air slows it down by just as much as gravity speeds it.