Acceleration due to gravity: ag

The force of gravity is a mutually attractive force that acts between objects. "Mutually attractive" means that all objects attract each other. The Earth does not just attract you, YOU also attract the Earth. The sum of these attractive forces equals your weight! Weight acts downward towards the center of mass of the Earth. Since this attractive force between objects acts downwards, objects that are free to move will fall, under the influence of gravity, in the direction of the force, downward.

Falling objects experience a positive acceleration as they fall. Near the surface of the Earth this positive acceleration is equal to 9.8m/s2. This means that any object that is free to fall near the surface of the Earth will accelerate downward at 9.80m/s2. In other words, its velocity will increase by 9.80m/s for every second it is falling.

The value 9.8m/s2 is known as the **acceleration due to gravity** and is designated by a lower case **"g"**. **1g = 9.80m/s2**. Since the acceleration due to gravity is known for any object, and a falling object accelerates at a constant rate, we can easily determine the velocity of a falling object at any point in its fall. For instance, if an object falls for 1.0s its velocity will be 9.80m/s. If an object falls for 2 seconds its velocity will be twice this or 19.6m/s. If an object falls for 3 seconds the final velocity will be 29.4m/s and so on. Mathematically this relationship looks like this: vf = ag x t. Final velocity = acceleration due to gravity x time. Look at the diagram below. The bowling ball is dropped from the top of the building. 4s after it is dropped it strikes the ground. The initial velocity of the ball, before it is dropped, is 0m/s. After it has fallen for 1s its velocity is 9.8m/s, after 2s its velocity is 19.6s, after 3s its velocity is 29.4s. The final velocity of the ball, just as it contacts the ground is 39.2m/s. So, if you want to calculate the velocity of a falling object just multiply the acceleration due to gravity times the fall time! vf = ag x t.