6.4. Free Fall

When an object falls under the influence of gravity alone, it is said to be in free fall.

Free fall refers to the motion of an object when it is falling solely because of the force of gravity. This means that no other forces, like air resistance or friction, are acting on the object while it falls. It is important to understand that free fall is a description of motion that involves only the gravitational pull of the Earth.

Think of a ball dropped from a height. As it falls, the only force acting on it is the pull of gravity, which pulls the ball straight down to the ground. If you were to drop it in a vacuum, where there is no air resistance, it would fall freely under the influence of gravity alone.

During free fall, the object accelerates towards the Earth. This acceleration is called acceleration due to gravity (g).

As an object falls freely, it accelerates at a constant rate because of the force of gravity. This acceleration is known as 'g' and is approximately 9.8 m/s² on the surface of the Earth. This means that for every second an object falls, its speed increases by about 9.8 meters per second. Understanding this acceleration helps us predict how fast an object will be moving after a certain period of time.

Imagine a skydiver jumping out of an airplane. At first, they are falling slowly, but as time passes, their speed increases rapidly due to gravity. Within seconds, they are moving much faster, illustrating the nature of acceleration due to gravity.

Value of g on Earth: 9.8 m/s².

The acceleration due to gravity (g) is not just a random number; it represents how strongly the Earth pulls objects towards itself. On Earth, this value is approximately 9.8 meters per second squared. This standard value is used in calculations when predicting how far and fast something will fall in a gravitational field.

If you were to drop a feather and a stone from the same height, the stone would hit the ground faster due to its greater mass. However, in a vacuum without air resistance, both objects would fall at the same rate of 9.8 m/s², demonstrating the uniform acceleration regardless of their mass.

In the absence of air resistance, all bodies fall with the same acceleration regardless of mass.

This statement emphasizes a fundamental principle of free fall: without air resistance, such as in a vacuum, all objects fall at the same rate. This means that it does not matter if an object is heavy or light; they will fall at the same speed when affected only by gravity. This counterintuitive concept stems from the fact that gravitational force increases with mass, but so does inertia, resulting in each object experiencing the same acceleration.

Consider two objects, a bowling ball and a tennis ball. If dropped from the same height in a vacuum (where there is no air), they would touch the ground at the same time, illustrating that their acceleration is identical despite their size and weight. This phenomenon is famously demonstrated in astronaut experiences on the moon, where they have dropped hammers and feathers that land simultaneously.

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