# Isaac Newton

Sir Isaac Newton (1642 - 1726)

Isaac was an English mathematician, astronomer, and physicist (known in his day as a natural philosopher). He is widely regarded as one of the most influential scientists of all time, and a key figure in the 17th century scientific revolution. In 1687, he published his most famous work Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), one of the most important physics texts ever written.

Isaac studied optics, motion, and mathematics, alongside astronomy. By observing the refraction of light by a prism, he discovered that white light is composed of all the colours in the spectrum. He concluded that a refracting telescope would suffer from dispersion, in that the white light would separate slightly into its component colours (called 'chromatic aberration'). He designed the first reflecting telescope, known today as a Newtonian telescope, to solve the problem.

According to the legend, Isaac was one day sitting under an apple tree in his garden, when an apple fell onto his head. Whilst there is no evidence that the apple actually hit Isaac on the head, he did see an apple fall from a tree, and wondered why it fell straight down, and not at an angle. He developed a theory of gravity, explaining everything from apples falling to the Earth's orbit around the Sun. This led to the publication of his Principia, which contained his famous Laws of Motion.

Isaac Newton's Laws of Motion are as follows: 1) A stationary body will stay stationary unless an external force is applied to it. 2) Force is equal to mass times acceleration, and a change in motion (change in speed) is proportional to the force applied. 3) For every action, there is an equal and opposite reaction.

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