Terminal velocity occurs when a falling object stops accelerating and falls at a constant speed. The word velocity itself refers to the rate that an object changes position. When an object falls there comes a time when it reaches a constant velocity, otherwise known as terminal velocity. This is because of the retarding force known as air resistance. Air resistance exists because air molecules collide into a falling body creating an upward force opposite gravity. This upward force will eventually balance the falling body's weight. It will continue to fall at constant velocity known as the terminal velocity. For a skydiver with parachute closed, the terminal velocity is about 200 km/h. The terminal velocity of this skydiver is about 124 mph (200 kph). "The terminal velocity of a falling human being with arms and legs outstretched is
about 120 miles per hour (192 km per hour) — slower than a lead balloon, but a good deal faster than a feather. (Hypertextbook.com,
accessed 21 Feb 2013).
The logical thing is to feel that if you drop objects of different weight from the same height, the heavier one will hit the ground
first. This is not necessarily the case. If one had to consider gravity alone, all falling bodies would fall with the same speed. But gravity is not the only factor that determines the speed of a falling object. Another factor to consider is air resistance. To understand terminal velocity
properly, we need to understand air resistance. Air resistance pushes against things which are moving. Air resistance pushes against a moving car and slows it down.
Air resistance pushes against falling objects and slows them down. (http://www.zephyrus.co.uk/airresistance.html accessed 21 Feb 2013). Air resistance is determined by the shape of the falling object. Air resistance is also known as drag. The more air resistance there is, the slower the object will fall. If you stand on a table and hold out your arms at the same length, and drop a tennis ball from one hand and a piece of paper from the other, the ball will fall faster because it provides less air resistance. The paper will fall slower than the ball does. But if you ball the paper up in your fist, and try the experiment again, you will find that they drop at similar speeds because you have changed the air resistance of the paper object. By the above you can see that air resistance has an impact on the determination of the speed of terminal velocity of an object.
Summary: Question - What is meant by the terminal velocity of a falling object? Answer – the speed reached when a falling object ceases to accelerate.