How Did Isaac Newton Discover the Laws of Motion?

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The apochryphal story of an apple falling on Sir Isaac Newton's head is likely one of the more famous stories about the discovery of a basic scientific process, even though there is no evidence he was hit by falling fruit. What is true, though, is that Newton's laws of motion are still being widely used today, to explain the kinds of objects and speeds you come across in everyday life.

TL;DR (Too Long; Didn't Read)

The story of Newton's falling apple is mainly legend – documents indicate he saw an apple fall, but there's no evidence he was hit by one – but while it may have given him the idea of figuring out gravity, the esteemed scientist only discovered the laws of motion after many years of studying math, physics, optics and astronomy.

Sir Isaac Newton's Falling Apple

Possibly the most famous legend in the history of science is that of the falling apple. The story goes that the young Isaac Newton was sitting in his garden when an apple fell on his head and he suddenly came up with his theory of gravity. The tale has been greatly exaggerated over the years, but there is proof that it happened. In 2010, the Royal Society in London digitally published the original manuscript that describes how Newton saw an apple fall from a tree in his mother's garden and began to work out his theory of gravity. This paper was written by a contemporary of Newton, William Stukeley, and describes a conversation Stukeley had with Newton, under the shade of an apple tree, about why an apple always falls towards the center of the earth. However, there is no evidence that the apple landed on Newton's head on any occasion.

Who Was Sir Isaac Newton?

Sir Isaac Newton, born in 1643, was one of the most influential scientists of all time. Expanding upon the ideas of previous prolific scientists like Galileo and Aristotle, he was able to turn theories into practice, and his ideas became the basis for modern physics.

Newton developed his laws of motion in 1666, when he was only 23 years old. In 1687, he presented the laws in his seminal work "Principia Mathematica Philosophiae Naturalis,” in which he explained how outside forces affect the movement of objects.

In developing his three laws Newton simplified objects, reducing them to mathematical points without size or rotation to let him ignore factors such as friction, air resistance, temperature and material properties, and focus on outcomes that can be illustrated wholly with reference to mass, length and time.

Newton's laws refer to the motion of objects in an inertial reference frame, which can be described as a system in which an object remains at rest or moves with constant linear velocity unless acted upon by external forces. Newton found that movement within such a system could be expressed using three simple laws.

Newton’s Three Laws of Motion

1. "A body at rest will remain at rest, and a body in motion will remain in motion unless it is acted upon by an external force." If an object is stationary, it will not begin to move by itself. If an object is moving, its speed and direction won't change unless something makes it change. This is often referred to as the "law of inertia."

2. "The force acting on an object is equal to the mass of that object times its acceleration." Objects will move farther and faster when they are pushed harder, and heavier objects need more force to move the same distance as lighter objects.

3. "For every action, there is an equal and opposite reaction." When an object is pushed in one direction, there is always an equal resistance from the opposite direction. This law can be used to explain how a rocket works: its powerful engines push down on the ground (the action) and the resistance from the ground pushes the rocket upwards with an equal force (the reaction).

What Is Newton's Legacy?

Newton's laws of motions, which have been verified by numerous experiments over the past 300 years, form the basis of the first branch of physics. This is now known as classical mechanics, the study of the motion of massive objects, and is the foundation upon which other branches of physics are built. Classical mechanics also has important applications in other areas of science, including astronomy, chemistry, geology and engineering.

References

About the Author

Claire is a writer and editor with 18 years' experience. She writes about science and health for a range of digital publications, including Reader's Digest, HealthCentral, Vice and Zocdoc.

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