Free-fall When an object falls under the influence of the Earth’s gravitational field it is said to fall freely.
The acceleration of free fall (g) on Earth is a constant. It is 10 m/s2. This acceleration is provided by the pull of Earth’s gravity which is 10 N/kg. All falling objects have the initial acceleration of 9.81 m/s2 or 10 m/s2. Usually we talk about free fall in air but remember this is only true when things fall from a few metres in air such as from a bench otherwise the acceleration is not constant. Acceleration is taken constant in the case of a few metres fall in air and when objects fall in a vacuum such on the moon. As there is no air resistance on the moon objects keep on accelerating and reach the ground faster than they would on the Earth. Velocity/time graph for a free falling object
Distance/time graph for a free falling object
Object falling down
REMEMBER
Object falling downward 1. The initial velocity is zero 2. Final velocity is a maximum
Object thrown upward the initial velocity is not zero final velocity is zero at the maximum height
Object being thrown up
Graph of an object thrown upward then coming back down to the ground.
Air resistance
It is friction due to air. When objects fall from a small height on earth, we ignore air resistance. The graph of v/t would look just as drawn above. When objects fall on the moon there is no air resistance so the graph is same. An elephant and a feather would take the same time to fall to ground. When objects fall from a greater height on earth and there is appreciable air resistance then the v/t graph looks different. An elephant would fall first and then the feather after a long time. The v/t graph will look like this.
As an object falls in air, its speed increases. As the speed increases the air resistance also increases. This reduces the resultant force and the acceleration decreases. When the air resistance becomes equal to the downward weight of the object, the resultant force becomes zero(0), the acceleration also becomes zero(0). đ?‘Ž đ?›ź đ??š. The object moves on with a constant velocity known as the terminal velocity after this point until it strikes the ground. It is easier for the air resistance to balance a feather than an elephant so the feather reaches its terminal velocity first while the elephant keeps on accelerating it hits the ground first.
Some examples of air resistance in use Air resistance pushes against falling objects and balances the weight. The object falls with a constant velocity (terminal velocity).
Air resistance pushes against a moving car and decreases its acceleration until it no longer can accelerate and travels with a constant speed (terminal velocity).