When you think about Isaac Newton, you probably think of the apocryphal story about an apple falling on his head, giving him the idea for the theory of gravity. You might also think about the fact that he is one of the most influential physicists and scientists of all time.

Born in 1642, Sir Isaac Newton was raised by his grandmother until the age of 12. His mother pulled him out of school at age 12 to have him tend the farm. Newton found farming monotonous, and he was soon sent back to school.

He studied law at Trinity College Cambridge, taking care of wealthier students' rooms to pay his bills. During his time at Cambridge, Newton kept a set of notes, entitled "*Quaestiones Quaedam Philosophicae*" ("*Certain Philosophical Questions*"). The notes reveal that Newton had already discovered the key ideas behind a new approach to mathematics: calculus. He graduated without honors or distinctions but did earn the title of scholar and four years of financial support for future education.

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In 1699, Newton received his Master of Arts degree. He also came across Nicholas Mercator's published book on methods for dealing with infinite series, which sparked a renewed interest in mathematics. He published a treatise, *De Analysi*, expounding his own ideas. This came to the attention of the mathematics community, and Newton was eventually given the Lucasian professorship at Cambridge.

Over the course of his life, Newton was responsible for a number of important ideas and theories. Let's take a look at just 7.

## Newton's Laws

In 1687, Isaac Newton developed his three laws of motion after discovering and studying gravity. They are:

- Every object stays in its state of rest or uniform motion unless disturbed by an external force. (Law of Inertia)
- Force equals mass times acceleration.
- For every action, there is an equal and opposite reaction.

## Orbital Cannon

Isaac Newton liked to play with ideas around the concept of universal gravitation. In thought experiments about it, he described a mountain that would be so tall it poked into space. He considered that if such a mountain existed, you could place a cannon on its peak to launch objects into orbit.

This was a way to explain how one object might orbit another.

He theorized that if you gave the cannonball the perfect amount of gunpowder on the launch, you could give it enough velocity to fall towards earth at the same rate the planet curved away from it. The cannonball would continue in free fall all the way around the planet, in effect, orbiting it.

## The Philosopher's Stone

Isaac Newton was not only interested in mathematics and physics, but he also worked in areas that strayed away from what we now consider more traditional science, and into the realm of alchemy and mysticism, including ways to concoct the magical philosopher's stone.

The "philosopher's stone" was a mythical substance that alchemists believed had magical properties, including being capable of bestowing the abilities of transmutation and immortality. In theory, the stone could turn lead into gold, or cure any disease.

It is important to remember that when Newton was alive, alchemy was still seen by some as legitimate science.

Documents that have recently come to light give Newton's handwritten instructions for making "philosophic" mercury. The document title translates, in part, to "*Preparation of the [Sophick] Mercury for the [Philosophers'] Stone*."

## Calculus

Isaac Newton and Gottfried Wilhelm Leibniz are said to have independently invented calculus at around the same time, although each claimed the other had stolen his work. Newton discovered that algebra and geometry weren't powerful enough for the science he was working on, so he developed a new means of mathematics in order to decode the world around him properly.

At its most basic, calculus is all about studying the rate of change of a quantity over time. In his work on gravity, Newton first tried to describe the speed of a falling object. When he did this, he found that the speed of a falling object increases every second, but that there was no existing mathematical explanation for this. The issue of movement and the rate of change had not yet been explored to any significant degree in the field of mathematics.

Newton also incorporated planetary ellipses into his theory of gravity, to try to explain the orbit of the planets. By using calculus, he could explain how planets moved and why the orbits of planets are in an ellipse.

One of his major breakthroughs was finding that the gravitational force that holds us to the ground is the same force that causes the planets to orbit the Sun and the Moon to orbit Earth.

## Refraction of Light

In 1704, Newton wrote a book on the refraction of light titled *Opticks.* It changed the way that scientists thought about light and color.

Scientists in the early 18th century knew that rainbows formed when the light was refracted through water, but they had no perception as to why this produced so many colors. The common theory was that the water "dyed" the rays of the sun or that color was created by the mixing of light and dark.

Beginning in 1666, Newton conducted studies with a lamp and a prism. Newton developed a setup that allowed him to refract the rainbow rays back into white light, which demonstrated that the white light is actually made up of a mixture of distinct colored rays, which are distinguishable when refracted in a prism. His experiments also revealed that color arose primarily from selective absorption of light by materials.

## Cooling

Newton became particularly interested in the physics of how things cool. During his studies, he particularly focused on red-hot iron balls in different fluids. He noticed that the difference in temperature between the iron ball and the air surrounding it ended up being less than **50 degrees Fahrenheit**, or roughly a difference of about **28 degrees Celcius**.

He established a correlation between the rate of heat loss and the temperature difference of the ball and fluid.

Newton's Law of Cooling states that the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings. This law has become a guiding principle in the field of thermodynamics.

## Gravity

While the legend is that Isaac Newton discovered the principles of gravity when he was hit by a falling apple, that story probably only has a grain of truth.

Whatever really happened, Newton realized that some force must be acting on falling objects, like apples, because otherwise, they would not start moving in the first place (see Newton's First Law of Motion).

Newton publicized his *Theory of Universal Gravitation* in the 1680s. It set forth the idea that gravity was a predictable force that acts on all matter in the universe, and is a function of both mass and distance. The theory states that each particle of matter attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

As Newton also began observing planets, he realized that the moon should just move in a straight line away from Earth unless there was a force keeping it close to our planet. This force was gravity.

The work of Newton actually helped prove that the Earth was not at the center of the solar system, rather that it moved along with other planets and orbited around the sun.