An interesting property of having an atmosphere is the concept of terminal velocity. Due to the air, the terminal velocity of an object is achieved through the balance of gravity and air resistance. Without air, gravity will continue to accelerate objects to the ground surface. Because there is air, objects achieve a steady speed of falling which is far less than the speed they would have without an atmosphere. Instead of accelerating to the surface, rain drops fall as a constant speed of near 10 meters per second near the surface. The terminal velocity depends on various factors including air density, what the object is made out of air, density of the object, surface area of object and shape(s) of the object. Because of these influences, different objects can fall at vastly different speeds (e.g. feather vs. hailstone). Factors that increase air resistance and lead to a slower fall rate: 1) denser air 2) less dense object 3) objects with lots of air bubbles (allows significant air penetration that increases air friction) 4) irregular shaped object (sphere shaped is least resistant while non-sphere shapes increase resistance) 5) large surface area (large surface area increases air resistance such as a parachute) As an object falls, the air resistance increases. Objects that are dropped from a fixed height will first fall primarily from the influence of gravity but as the object accelerates it will encounter a greater and greater air resistance. Eventually the object will fall at a fixed speed. To obtain this fixed speed the object must be dropped from high above the Earth’s surface or it must have a very high air resistance. |