Newton

Why do objects move in the ways they do?

Isaac Newton

• Born in 1642 (by coincidence, the same year of Galileo’s death.

• Born very prematurely in a small town in rural England (never expected to survive)

• He never knew his father (he died three months before Isaac was born)

• Isaac went away to grammar school at 15

• He returned to the farm at 18, but was a terrible farmer

• An uncle persuaded his mother to allow him to go to college which he did in 1661.

• He paid his way through Cambridge by waiting tables and cleaning rooms for wealthier students and faculty

Newton’s Home

Plague

• Just as Newton had finally been awarded a scholarship at Cambridge in 1665, the Plague invaded England. To escape its effects, Cambridge was shut down and Newton retired for two years in the countryside.

A Productive Time• Newton’s two years in the

countryside were possibly two of the most productive for one person in the history of science.

• During this time Newton wrote that he first understood the law of gravitation, the law of optics, and invented calculus, as well as create his laws of motion.

• A legend is that gravity unveiled itself when an apple fell on his head!

• All this while only 23 and 24 years old.

Newtonian Motion

• Newton’s famous laws on motion were collected in a book he reluctantly wrote called “The Principia”

• It took much convincing from Edmund Halley before he would publish his physics findings.

Newton’s First Law

• An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

• We can see that this law was an extension of what Galileo said, so Newton’s first law is also known as the Law of Inertia

Inertia

• Inertia is the tendency of an object to remain at rest or in motion unless acted upon by an unbalanced force.

• Inertia is measured as the mass of an object (in Kg)

• Inertia Demos: Cards n’ Coins; Table Cloth, Heavy Ball Light Ball, Car Crash

Newton’s Second Law

• F=ma• Newton gave the world a way to talk

quantitatively about Force• He was able to relate an object’s Inertia to

its Acceleration, based on the Force applied to it.

• F is force in the above equation and is measured in Newtons (named for him not by him)

F=ma

• Think: It takes a force (a push or pull) to make an object accelerate

• m stands for mass• a is acceleration• Force is the product of these.• The unit of mass is the kilogram, the unit of

acceleration is m/s2.• The unit of force is therefore the product of these

units: kg m/s2 (referred to as the Newton)

Newton vs. Aristotle

• According to Newton, and his law: F=ma, an object needs a net force greater than zero in order to have any acceleration (change in velocity)

• An object at rest or traveling at a constant velocity has no net force acting on it (no acceleration)

• The airplane stays at a level height and a constant velocity due to the fact that all forces on it are balanced.

The Newton

• The Unit of force used in SI is the Newton.

• Since f=ma and m=kg, and a=m/s²

»F=kg•m/s²

• The unit kg•m/s² is known as the Newton

Example:• What is the force on a

100 kg object accelerating at 9.8m/s²?

• F=ma F=100kg•9.8m/s²

= 980 kg•m/s²

or 980 N

Newton’s Third Law

• For every action there is an equal and opposite reaction.

• This explains why a rocket fires up into space, why astronauts can move about in space using jets of air, and why an object can rest on a table top.

Newton’ Paraphrase

"We are like dwarfs sitting on the shoulders of giants. We see more than they do, indeed even farther; but not because our sight is better than theirs or because we are taller than they. Our sight is enhanced because they raise us up and increase our stature by their enormous height"

Newton

• “If I have seen further it is by standing on the shoulders of giants”

(meaning Archimedes, Aristotle, Kepler, Brahe, Copernicus and Galileo etc.)

Personality

• Newton was a classic introvert

• He could concentrate on one topic for many hours

• He loved his pet

• He was extremely modest (he refused to publish his work until coaxed)

• He also had many strange habits…

• He published his work in Latin only.

• Here is a picture of his one of is notebook pages.