Sir Isaac Newton Fundamentals to physics
Gravitation
With all the things that Isaac Newton did some of his most renowned works was
with that of gravitation. Newton was one of the foremost scientific intellects so fall time.
Newton is also considered one of, if not the most influential astronomers of all time (web
1). Besides his contributions to this field he gave physicists an easier way and more
comprehendible way of doing physics. This was due to these three laws that he came up
with that where named after him. They were as follows:
Newton’s First Law
A body at rest will remain at a rest or a body in motion will remain in constant motion
unless a force is applied to it.
Newton’s Second Law
F=ma
(Force= Mass x Acceleration)
(One of the most used equations in physics)
Newton’s Third Law
For every force there is an equal and opposite reaction.
Newton’s first law applies to anything that is in motion or standing still. It goes on
to say that everything will stay the way it was unless a force is applied to it (Holliday).
Like a ball will stay in one place forever if nothing ever applies a force to it. Newton’s
second law applies to just about every single equation that we use today in physics. This
equation gives us the acceleration due to gravity, 9.8 meters per second. It is also used in
every equation that has a mass in it because it gives the weight of the mass when it is
derived. Newton’s third law is basic common sense that says that when something gives a
force there is an equal force being applied to it. Like when you push on a wall the wall
pushes back with the same force and also the earth pulling down on you, you are pushing
on the earth(web 3). Besides these three laws that Newton gave us he also gave us the
reason behind why the moon doesn’t fall out of the sky (web 4).
To understand some of the principles in this paper you have to understand some
of the language that is used in physics. One term that is used is “in a Newtonian world”.
This refers to the fact that a lot of Newton’s principles only work if there is no friction at
all. This means no air friction acting on objects and no friction form the ground on
objects. This makes it so there is nothing resisting the objects as they fall or move. One
example of this can be seen in figure 1. In this figure you can see that the feather and an
apple are falling at exactly the same rate. But how can this be, everyone know that an
apple will hit the ground before a feather but in the picture they fall at the same rate? This
is because there is no friction in this picture all of the air has been sucked out of the
room-causing there to be no friction. From this only one force is acting on the feather and
apple and that is gravity. They both fall at 9.8 meters per second and so they both hit the
ground at exactly the same time. This only happens with no friction and is usually
accomplished when all the air is sucked out of a room with a compressor or other device
that takes air out of a room (Holliday).
One of my favorite and interesting demonstrations with gravity is also proven
with Newton’s three laws. This is when two balls of equal mass are shot and dropped at
exactly the same time. When this is done the ball that is dropped is expected to hit the
ground first before the one that is shot does but they both fall at the same rate and hit at
the same time as you can see in figure 2. This is because gravity is acting on the two balls
with the same force down. Having them both falls at 9.8 meters per second has them hit
at exactly the same time. This also applies to a bullet when it is fired and dropped at the
same time in a Newtonian world. But as you can guess it only happens in a Newtonian
world because there is no air friction then. But since there is air frictional and the bullet is
designed not to fall because of its shape and spin that it is given a bullet that is dropped
will hit the ground before the bullet that is fired will. This still amazes me every time I
see it because the two balls do hit at the same time (Holliday).
Newton applied these three laws to Kepler’s laws of orbit to come up with the law
of universal gravitation. This gave us the reason why the moon doesn’t fall out of the sky
and hit the earth (web 2). This came about through a well-known story; it was on seeing
an apple fall in his orchard that Newton conceived that the same force governed the
motion of the Moon and the apple (web1). He calculated the force needed to hold the
Moon in its orbit, as compared with the force pulling an object to the ground. Newton
identified gravitation as the fundamental force controlling the motions of the celestial
bodies. He never found its cause. To contemporaries who found the idea of attractions
across empty space unintelligible, he conceded that they might prove to be caused by the
impacts of unseen particles (web 1).
He thought out the fundamental principles of his theory of gravitation, namely,
that every particle of matter attracts every other particle, and he suspected that the
attraction varied as the product of their masses and inversely as the square of the distance
between them (web 5). Leaving out the details and only taking round numbers, his
reasoning at this time on the theory of gravitation seems to have been as follows. He
suspected that the force, which retained the moon in its orbit about the earth, was the
same as terrestrial gravity ( web 4). He knew that, if a stone were allowed to fall near the
surface of the earth, the attraction of the earth caused it to fall 9.8 meters per second. The
moon's orbit relative to the earth is nearly a circle, taking it to be so, he knew the distance
of the moon, and therefore the length of its path; he also knew that the time it took the
moon to go around the earth once was a month.
From this he could easily find its velocity at any point such as M on figure 3. He
could from there find the distance MT through which it would move in the next second if
it were not pulled by the earth's attraction. At the end of that second it was however at M',
and from that the earth E must have pulled it a distance TM' in one second (assuming the
direction of the earth's pull to be constant). Now he and several physicists of the time had
conjectured from Kepler's third law that the attraction of the earth on a body would be
found to decrease as the body was moved farther away from the earth and inversely from
the center of the earth. If this were the actual law, and if gravity were the sole force which
retained the moon in its orbit, then TM' should be 9.8 meters per second inversely as the
square of the distance of the moon from the center of the earth to the square of the radius
of the earth. Later when Newton repeated the investigation, TM' was found to have the
value which was required by the hypothesis, and the verification was complete; but in
1666 his estimate of the distance of the moon was inaccurate, and when he made the
calculation he found that TM' was about one-eighth less than it ought to have been on his
hypothesis (web 4). This didn’t however discourage his faith in the belief that gravity
extended as far as the moon and varied inversely as the square of the distance. It seems,
moreover, that Newton already believed firmly in the principle of universal gravitation,
that is, that every particle of matter attracts every other particle, and suspected that the
attraction varied as the product of their masses and inversely as the square of the distance
between them (web 4).
And that was just some of the major parts that Newton gave future physicist to
think about. He was very helpful in this department and if it wasn’t for his conjectures it
might have set back physics decades before someone else ever came accost it again and
proved it as he did.