When we throw a ball up into the air, we observe that after its initial pick-up, the speed retards gradually and becomes zero for a fraction of a second before it starts falling back to the ground. While falling down, it should be noted that the initial speed is low but picks up later.
The ball falls to the ground because it is pulled towards the earth by the force of gravity. The earth attracts all objects towards its centre with a force known as the force of gravity. Due to this force of gravity, all falling objects acquire an acceleration which is called the acceleration due to gravity. It is denoted by ‘g’.
The acceleration due to gravity accelerates the ball roughly by 9.8 m per sec. per sec. (32 feet per second per second). This means that each second the object would move 9.8 metres faster than the previous second. The speed of the ball at different intervals of time varies as follows.
To begin with, the ball or the falling object is stationary or its speed is zero metre per second when it starts falling. At the end of the 1st second it travels 9.8 m per second. At the end of 2 seconds it moves 19.6 m per second and at the end of 3 seconds, 29.4 m per second and so on. In fact, every second the object falls 9.8 m faster than its speed in the previous second.
The acceleration of a body or object falling freely in a vacuum varies slightly from place to place due to slight variations in the gravitational pull as the distance of the places from the centre of the earth varies to some extent. At London its value is 9.807 m per second per second, at North Pole 9.8 m per second per second, and at equator 9.79 m per second per second. At the sea-level in Washington it is 9.8008 m per second per second. Acceleration due to gravity is defined as the rate of change of velocity of the falling object with respect to time due to the force of gravity. Because it is a measure of rate of change of velocity, it is expressed in metres per second per second.
One of the important points to note about the falling objects is that however heavy they might be, they all fall at the same rate. However, air resistance may have some effect on the speed of falling objects. This fact was demonstrated by the famous scientist Galileo by dropping a heavy cannon ball and a light musket ball at the same time from the Leaning Tower of Pisa. Both the objects arrived at the ground at the same time.
The resistance of the air is the main reason why some objects fall faster than the others. A feather, for example, floats slowly downwards because it faces more air resistance due to its relatively large surface for the air to act on. A smooth, pointed bullet will fall faster than a feather because it experiences less resistance of air. In the vacuum both will fall with the same speed because the air resistance would not be there.
