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.