Have you ever looked at a sky full of stars and wondered what held this all together?
Have you ever accidentally dropped your phone on the ground and questioned why it
behaves like that? I believe that most of us probably wouldn’t because these are just
things we see–and unfortunately, do by accident–in our daily life. The stars are there
because they are there and the phone dropped because we had butter fingers.
It seems these things are not worth wondering about or questioning–or are they?
Most people wouldn’t bother thinking beyond what they see. But some special people
do.
There was one man in human history that questioned these seemingly simple everyday
things and by questioning them he expanded our understanding of the entire universe.
He was the famous Sir Isaac Newton.
On a warm night, the young Newton went into his garden after having dinner. He sat
under an apple tree and was sipping his cup of tea and enjoying the night when
something happened. It was a simple, everyday occurance: an apple fell from a tree.
But that moment made history and would lead to some of the greatest scientific ideas
ever imagined
”Why should that apple always descend perpendicularly to the ground?“ he thought to
himself.
Instead of cursing the apple for disturbing his after-dinner repose, he was stimulated
into thinking about something that was still an unsolved mystery at that time, gravity.
He dove into research and eventually published a physics law that would become
recognized as a fundamental principal of modern physics: The Newton’s Law of General
Gravity.
OK, what is Newton’s Law of General Gavity?
Most of us just think of something falling as “falling down.” But is it really “down?” The
earth isn’t flat, it’s round, so unless we are standing at the exact point that is the “top,”
we are actually standing “sideways,” that is, “up and down” are actually just relative to
the round earth. To complicate matters, the round Earth is moving though space, which
has no “up” or “down” at all, so “down” just means “where gravity takes something.”
So, what is gravity anyway?
It’s an attractive force.
It’s an attractive force that is between every objects that have mass, which to simplify
things I’ll just call measurable weight and substance. No matter if it is between the
pennies in your pocket or between you and your friends, or between your cell phone and
the ground, there is always an attractive force between every object, pulling them
together.
OK, if that’s true, why doesn’t my cell phone stick to me instead of falling to the ground?
Because the amount of attractive force pulling the two objects together depends upon
the mass of the objects. If the product of the two masses is too small to be significant,
they won’t be pulled together—or if there is something really big nearby, the “falling”
object will “fall” towards it because that big thing has the most mass and hence will
have the greatest pulling force.
The gravitational pull between two masses also depends on the distance between them:
the further away the two masses are, the smaller the resultant force is, and vise versa.
The reason that we always feel like the gravity of the earth is the same is because our
distance towards the centre of the earth is more or less equal wherever we are on the
surface of the planet.
OK, what if we were not standing on the surface?
The radius of earth is about 6370 kilometers. If we changed our relative distance from
the center by going higher by a rocket or digging deeper by a super drill (not those kid’s
toys you use at the beach), you would discover that the gravitational pull of the earth
actually changes: in outer space, it is weaker, at the earth’s core, it is stronger.
But one thing does not change, the pull is always in a straight line, like a rope between
two objects, hence, what Sir Issac observed: objects always fall perpendicular to the
ground.
So next time when you see something falling, try to think of Newton instead of blaming
yourself or the object. By the way, do you know that you will experience something that
violates the Newton’s Law of General Gravity when you are reading science writings?
You just can’t put them down! Stay tuned!