Why does an object in free fall accelerate?

An object in free fall accelerates due to the force of gravity acting upon it.

In more detail, the concept of free fall is a key principle in physics. It refers to any motion of a body where gravity is the only force acting upon it. In the absence of other forces, such as friction or air resistance, an object in free fall experiences a constant acceleration towards the centre of the Earth. This acceleration is known as the acceleration due to gravity, and on Earth, it has an approximate value of 9.81 m/s².

The force of gravity is a result of the mass of the Earth attracting the mass of the object. According to Newton's second law of motion, force equals mass times acceleration (F=ma). In the case of free fall, the force is the weight of the object, which is its mass times the acceleration due to gravity. As the force of gravity acts downwards towards the centre of the Earth, the object accelerates in the same direction.

This acceleration is constant, meaning the object's velocity increases by approximately 9.81 m/s every second it is in free fall. For example, after one second, its velocity would be 9.81 m/s, after two seconds, 19.62 m/s, and so on. This continues until the object encounters a force that counteracts gravity, such as the ground or air resistance.

It's important to note that all objects in free fall accelerate at the same rate, regardless of their mass. This was famously demonstrated by Galileo, who dropped two spheres of different masses from the Leaning Tower of Pisa and found they hit the ground at the same time. This principle is also why astronauts in space appear to be weightless - they are in constant free fall towards the Earth, but their forward motion keeps them in orbit.

In conclusion, an object in free fall accelerates because of the force of gravity. This force, acting alone, causes the object to speed up as it moves towards the Earth, demonstrating the principle of acceleration due to gravity.