Let us learn from one the most interesting anecdotes in science. It is a serious academic play and you will enjoy it, at the least.
Remember, Isaac Newton was sitting under the apple tree in his father’s farm, escaping from the plague in the city of London, where he was studying. He was barely 12 years old! Then the unexpected happened. Was it really the unexpected?! Anyway, whatever, it happened!
One of the fruits of the tree, an apple, fell and hit him on the head, before dropping to the ground, I guess. There was no evidence to support the apple hitting him on the head, anyway. That is no issue here. It fell; he saw it and the experience inspired something really great.
Isaac Newton discovered the force and the law of gravitation many years after the apple experience. There are three stages to this interesting and inspirational narrative: “before the fall”, “during the fall” and “after the fall”.
Before The Fall
Needless bothering ourselves with the processes that made the fruit grew from the tree; photosynthesis, absorption, osmosis to just name. Now, it must ripen and be ready to be eaten! That process, as well as the others mentioned is biological.
There are two forces acting on the apple. One: the gravitational pull that draws it down. It is a natural force that connects all objects to the center of the earth. Two: the tensional force in the short rope-like tissue that connects the fruit to the branch of its tree.
Mathematically, these two forces balance. As a result, Isaac Newton’s Third Law of Motion operates: “for every action there is an equal and opposite reaction”. Can the apple refuse to fall, after ripening? Hmmmm! It must have to fall down one way or the other. The pull of gravitational force will soon be greater than the tensional force. As it ripens, it surely becomes heavier, the mass increases and it will eventually fall down.
Anyway, if it refuses to fall, it will, after ripening, begin to rot. The chemical processes inside the fruit make it wears out and it tears out from inside. Even then, it falls off! There are two classes of mechanical energy: Potential (position or height related) and Kinetic (motion or movement related) we must play with in this analysis. For the apple at this stage, it has the first. Its potential energy is likened to that of stretched spring because of its hanging loosely. Also the higher its place on the tree determines the magnitude of this energy.
During The Fall
When, eventually, the fruit; the apple, drops, the force of gravity becomes greater than the tensional force in the connecting tissue. The former will have already thinned out and loses it strength.
All along, even while the fruit was growing, the mass was also increasing. The mass of object is an undeniable part of the effect of the gravitational pull on it:
F = mg
F is the gravitational force, m is the mass of the object and g is the acceleration due to gravity.
Gravity! Gravity!! Gravity!!! It is always recurring, once a body is within the gravitational field, the effect will always be felt. As the apple drops downward, it turns into a free-fall that has a few basic rules.
That free-fall of the apple must have a uniform acceleration, g. That value is a constant of 9.8 or 10.0 meter per square second. All free-falling bodies have that value of acceleration, irrespective of their masses.
That constant acceleration, g, can be studied and understood clearly, if the length of distances covered by the apple is measured and timed. At the start of the free-fall, the distance in relation with the time is small, but towards its end, the relationship becomes larger. Nonetheless, it is fact that the acceleration, g, remains constant throughout.
Second to that, is that the velocity increases, which means that the potential energy we knew about earlier, changes into kinetic energy. Take note here, that the principle of the conservation of energy is obeyed; potential changes to kinetic energy as position changes to motion.
We must also be aware that the mass of the apple will remain the same; constant, throughout the journey. To reiterate, the velocity increases and the acceleration remains constant.
What if it hangs mid-air? Without mincing words, it is near impossible, because air-resistance rarely obstructs or affects free-falling bodies. But what if?! In such case, it will float. Then, the attention shifts from Isaac Newton to Archimedes. For a body to float in a fluid- apple floating in air, its weight (gravity again!), must equal the Upthrust (upward reactionary force) it experiences from the fluid; in this case air. That takes the scenario back to Isaac Newton’s Third Law of Motion. Not to worry, it will not float, because the apple’s mass and force of gravity are greater than the Upthrust.
After the fall
This is the third and final stage. The force of gravity finally brings the apple “down to earth”. It was expected! All of these will happen in a spate of seconds. What are new possibilities or realities? The motion seizes as the velocity becomes zero and acceleration due to gravity, g, vanishes. On the ground, the earth, the height the apple had while hanging on the tree, will also become zero.
The kinetic energy occasioned by the motion of the free-fall turns back to the potential energy it was when hanging. But not all! Some of the kinetic energy is lost through sound energy from the impact and heat energy, too.
A little dent is possible, too. As the apple hits the ground, which can be a hard surface, the Third Law of Motion comes to play again. The reaction of the ground can leave a little dent on the apple, making it to lose some liquid juice and reducing its mass. Anyway, that is always negligible.
Where is Isaac Newton in this?
According to the story, the apple came straight down hitting Isaac Newton on the head before dropping to the ground. The story also reported that he picked it up and began to ponder on the possible reasons the apple fell, but never flew away.
Newton must have felt some tingling pains from the impact. Only God knows whether he rubbed the spot slightly or vigorously to assuage the pain. Who knows?
William Stukeley, Isaac Newton’s younger contemporary, an antiquarian and proto-archaeologist, wrote the following in a meticulously handwritten manuscript released by the Royal Society:
“Amid other discourse, he told me, he was just in the same situation, as when formerly the notion of gravitation came into his mind. Why sh[oul]d that apple always descend perpendicularly to the ground, thought he to himself; occasion’d by the fall of an apple, as he sat in contemplative mood”.
“Why sh[oul]d it not go sideways, or upwards? But constantly to the Earth’s centre? Assuredly the reason is that the Earth draws it. There must be a drawing power in matter. And the sum of the drawing power in the matter of the Earth must be in the Earth’s centre, not in any side of the Earth”.
“Therefore does this apple fall perpendicularly or towards the centre? If matter thus draws matter; it must be proportion of its quantity. Therefore the apple draws the Earth, as well as the Earth draws the apple.”
Akanji G. Olaniyi