3.11:
Free-falling Bodies: Introduction
When an object falls towards the ground and is only influenced by gravity, it is said to be in free-fall.
Consider a ball thrown upwards in the air, reaches a certain height before falling back due to Earth's gravitational force.
Here, the ball is undergoing changes in velocity during its fall, but the acceleration is constant.
Consider a paper and a stone both being dropped at the same time and from the same height. Which object will reach the ground first?
It is observed that the stone reaches the ground first, followed by paper. This is due to the air resistance, which is negligible for the heavy objects.
However, if the objects are dropped together from the same height in a closed vacuum box, they will reach the base of the box at the same time.
Therefore, if the air effects are ignored, all objects irrespective of their masses, fall with a constant acceleration, known as acceleration due to gravity, which has an approximate value of 9.8 m/s2.
3.11:
Free-falling Bodies: Introduction
All objects, neglecting air resistance, fall with the same acceleration towards the Earth's center due to the force exerted by the Earth's gravity. This experimentally determined fact is unexpected because we are so accustomed to the effects of air resistance and friction that we expect light objects to fall slower than heavier ones. People believed that a heavier object had a greater acceleration when falling until Galileo Galilei (1564–1642) proved otherwise. We now know this is not the case.
The motion of an object under the influence of gravitational force is called a free-fall. Free-fall motion is not only associated with objects dropped from rest, but with all objects moving freely under gravity's influence. The acceleration of objects under a free-fall is constant, and is known as acceleration due to gravity, g. The magnitude of acceleration due to gravity is 9.8 m/s2. Because of the constant acceleration, kinematic equations of motion can be used to predict the dynamics of objects under free-fall, provided that the air effects are neglected.
In the real world, however, air resistance is always present, and it opposes the motion of objects. The momentum required to oppose the motion of heavier objects is larger compared to lighter objects. Therefore, heavier objects fall faster towards the ground during free-fall in the presence of air resistance.
This text is adapted from Openstax, University Physics Volume 1, Section 3.5: Free-fall.