Study of motion _____________________________________________________________________________________________
18. Vertical motion due to gravity: free fall Figure 8.9
Free fall is a specific case of UALM.
Naturally, objects fall. This is due to gravity of the Earth.
If you drop your pen, it starts from an initial position, at rest, and as it falls, we can observe that it moves faster. There is an increase in velocity during the fall, the pen is accelerating.
In free fall, all objects are moving with a constant acceleration of -9,8 m/s2 , which we usually represent with the letter g (because it is due to gravity).
This negative sign represents only the direction of acceleration due to gravity. So, 'g' is negative in free fall because the direction of 'g' is opposite to the positive direction defined as positive (in the vertical, positive upwards and negative downwards).
The picture shows an initially-stationary ball which is allowed to fall freely under gravity, and drops a distance which is proportional to the square of the elapsed time