Issac Newton and His Three Laws of Gravity

What did Isaac Newton say about being the father of the scientific revolution?

"If I have seen farther than other men, it is because I stood on the shoulders of giants."

Isaac Newton (1642-1727)

1. English scientist and mathematician who wrote the "Principia Mathematica" 2. Viewed the universe as a vast machine governed by the universal laws of gravity and inertia 3. Mechanistic view of the universe strongly influenced deism English scientist who formulated the law of gravitation that posited a universe operating in accord with natural law.

Gravity

A force that pulls objects toward each other. A force of attraction between objects that is due to their masses.

momentum is equal to its velocity times its mass

A paper clip tossed across a room has low velocity and therefore little momentum, and you could easily catch it in your hand. But the same paper clip fired at the speed of a rifle bullet would have tremendous momentum, and you would not dare try to catch it.

Nature and Nature's laws lay hid in night: God said, "Let Newton be!" and all was light.

Alexander Pope

What did Aristotle believe about the nature of motion?

Aristotle said that the world is made up of four classical elements: earth, water, air, and fire, each located in its proper place. The proper place for earth (meaning soil and rock) is the center of the universe, and the proper place of water is just above earth. Air and then fire form higher layers, and above them lies the realm of the planets and stars. The four elements were believed to have a natural tendency to move toward their proper place in the cosmos. Things made up mostly of air or fire—smoke, for instance—tend to move upward. Things composed mostly of earth and water— wood, rock, flesh, bone, and so on—tend to move downward. According to Aristotle, objects fall downward because they are moving toward their proper place.* Aristotle called these motions natural motions to distinguish them from the violent motions that are produced when, for instance, you push on an object and make it move other than toward its proper place. According to Aristotle, such motions stop as soon as the force is removed. To explain how an arrow could continue to move upward even after it had left the bowstring, he said currents in the air around the arrow carried it forward even though the bowstring was no longer pushing it.

every action there is an equal and opposite reaction

Forces must occur in pairs directed in opposite directions.

Mathematical Discourses and Demonstrations Concerning Two New Sciences, Relating to Mechanics and to Local Motion (Two New Sciences)

Galileo published his work on motion in 1638, two years after he had become entirely blind and only four years before his death. The book is a brilliant achievement for a number of reasons. To understand motion, Galileo had to abandon the authority of the ancients, devise his own experiments, and draw his own conclusions. In a sense, this was the first example of experimental science. But Galileo also had to generalize his experiments to discover how nature worked. Though his apparatus was finite and his results skewed by friction, he was able to imagine an infinite, frictionless plane on which a body moves at constant velocity. In his workshop, the law of inertia was obscure, but in his imagination it was clear and precise.

Colonel David Scott

He stood on the airless moon, demonstrated the truth of Galileo's discovery by simultaneously dropping a feather and a steel geologist's hammer. They fell at the same rate and hit the lunar surface at the same time.

What did Galileo turn to after studying natural motion?

He turned his attention to violent motion—that is, motion directed other than toward an object's proper place in the cosmos. Aristotle said that such motion must be sustained by a cause. We would say "a cause" today. Galileo pointed out that an object rolling down an incline is accelerated and that an object rolling up the same incline is decelerated.

Why was Galileo significant in gravity

He was the defender of Copernicanism who made the first use of an astronomical telescope, but he also was the first scientist who carefully studied the motions of falling bodies. That was the key information that led Newton to understand gravity.

How did Galileo influence Newton's First Law of Gravity - Inertia?

If the incline were perfectly horizontal and frictionless, he reasoned, there could be no acceleration or deceleration to change the object's velocity, and, in the absence of friction, the object would continue to move forever. Motion need not be sustained by a cause, said Galileo. Once begun, motion continues until something changes it. In fact, Galileo's statement is a perfectly valid summary of the Law of Inertia, which became Newton's First Law of Motion.

violent motions

In Aristotelian physics, motion other than natural motion. produced when, for instance, you push on an object and make it move other than toward its proper place.

natural motions

In Aristotelian physics, the motion of objects toward their natural places - fire and air upward and earth and water downward.Motion that an object does naturally w/o being acted upon by outside sources/violent motion. Aristotle idea that all elements had a natural place that they naturally go to without violent motion. According to Aristotle, objects fall downward because they are moving toward their proper place.*

What did scholars refer to when trying to resolve controversy, huge questions or problems?

In Galileo's time and for the two preceding millennia, they had tended to resolve problems by referring to authority. To analyze the flight of a cannonball, for instance, they would turn to the writings of Aristotle and other classical philosophers and try to deduce what those philosophers would have said on the subject. This generated a great deal of discussion but little real progress. Galileo broke with this tradition when he conducted his own experiments.

I can calculate the motion of heavenly bodies, but not the madness of people.

Isaac Newton

Law of Inertia

Newton's first law. A law formulated by Galileo that states that motion, not rest, is the natural state of an object, and that an object continues in motion forever unless stopped by some external force.

Experimental Science

Science that begins with and depends on careful experiments and measurements. Though Galileo's apparatus was finite and his results skewed by friction, he was able to imagine an infinite, frictionless plane on which a body moves at constant velocity. In his workshop, the law of inertia was obscure, but in his imagination it was clear and precise.

What did Aristotle say about these two laws

Such motions stop as soon as the force is removed. To explain how an arrow could continue to move upward even after it had left the bowstring, he said currents in the air around the arrow carried it forward even though the bowstring was no longer pushing it.

What did Galileo Begin Studying?

The motions of falling bodies, but he quickly discovered that the velocities were so great and the times so short that he could not measure them accurately. Consequently, he began using polished bronze balls rolling down gently sloping inclines. In that instance, the velocities are lower, and the times are longer. Using an ingenious water clock, he was able to measure the time the balls took to roll given distances down the incline, and he correctly recognized that these times are proportional to the times he would have measured using falling bodies. Galileo found that falling bodies do not fall at constant rates, as Aristotle had said, but are accelerated. That is, they move faster with each passing second. Near Earth's surface, a falling object will have a velocity of 9.8 m/s (32 ft/s) at the end of 1 second, 19.6 m/s (64 ft/s) after 2 seconds, 29.4 m/s (96 ft/s) after 3 seconds, and so on. Each passing second adds 9.8 m/s (32 ft/s) to the object's velocity. In modern terms, this steady increase in the velocity of a falling body by 9.8 m/s each second (usually written 9.8 m/s^2) is called the acceleration of gravity at Earth's surface. Galileo also discovered that the acceleration does not depend on the weight of the object. This, too, is contrary to the teachings of Aristotle, who believed that heavy objects, containing more earth and water, fell with higher velocity. Galileo found that the acceleration of a falling body is the same whether it is heavy or light. According to some accounts, he demonstrated this by dropping balls of iron and wood from the top of the Leaning Tower of Pisa to show that they would fall together and hit the ground at the same time. In fact, he probably didn't perform this experiment. It would not have been conclusive anyway because of air resistance.

Galileo and Motion

The natural state of an object is one of rest or constant velocity. An object at rest tends to stay at rest and an object in motion tends to stay in motion. Galileo began studying the motion of freely moving bodies even before he built his first telescope. After the Inquisition condemned and imprisoned him in 1633, he continued his study of motion. He seems to have realized that he would have to understand motion before he could truly understand the Copernican system. In addition to writing about a geocentric universe, Aristotle also wrote about the nature of motion, and those ideas still held sway in Galileo's time. Aristotle said that the world is made up of four classical elements: earth, water, air, and fire, each located in its proper place. The proper place for earth (meaning soil and rock) is the center of the universe, and the proper place of water is just above earth. Air and then fire form higher layers, and above them lies the realm of the planets and stars. The four elements were believed to have a natural tendency to move toward their proper place in the cosmos. Things made up mostly of air or fire—smoke, for instance—tend to move upward. Things composed mostly of earth and water— wood, rock, flesh, bone, and so on—tend to move downward. According to Aristotle, objects fall downward because they are moving toward their proper place.* Aristotle called these motions natural motions to distinguish them from the violent motions that are produced when, for instance, you push on an object and make it move other than toward its proper place. According to Aristotle, such motions stop as soon as the force is removed. To explain how an arrow could continue to move upward even after it had left the bowstring, he said currents in the air around the arrow carried it forward even though the bowstring was no longer pushing it. In Galileo's time and for the two preceding millennia, scholars had tended to resolve problems by referring to authority. To analyze the flight of a cannonball, for instance, they would turn to the writings of Aristotle and other classical philosophers and try to deduce what those philosophers would have said on the subject. This generated a great deal of discussion but little real progress. Galileo broke with this tradition when he conducted his own experiments. He began by studying the motions of falling bodies, but he quickly discovered that the velocities were so great and the times so short that he could not measure them accurately. Consequently, he began using polished bronze balls rolling down gently sloping inclines. In that instance, the velocities are lower, and the times are longer. Using an ingenious water clock, he was able to measure the time the balls took to roll given distances down the incline, and he correctly recognized that these times are proportional to the times he would have measured using falling bodies.

momentum

The product of an object's mass and velocity. a measure of its amount of motion.

Where was Isaac Newton Born?

Woolsthorpe, England, on December 25, 1642, and on January 4, 1643.England in Woolsthorpe, England, on December 25, 1642, and on January 4, 1643. This was not a biological anomaly but a calendrical quirk. Most of Europe, following the lead of the Catholic countries, had adopted the Gregorian calendar, but Protestant England continued to use the Julian calendar. So December 25 in England was January 4 in Europe. If you use the English date, then Newton was born in the same year that Galileo Galilei died. Newton became one of the greatest scientists who ever lived, but even he admitted the debt he owed to those who had studied nature before him. He said, "If I have seen farther than other men, it is because I stood on the shoulders of giants."

Newton's first law of motion

a restatement of Galileo's law of inertia. An object continues at rest or in uniform motion in a straight line unless acted on by some force. Astronauts drifting in space will travel at constant rates in straight lines forever if no forces act on them. Newton's first law also explains why a projectile continues to move after all forces have been removed—for instance, how an arrow continues to move after leaving the bowstring. The object continues to move because it has momentum. You can think of an object's momentum as a measure of its amount of motion. An object's momentum is equal to its velocity times its mass. A paper clip tossed across a room has low velocity and therefore little momentum, and you could easily catch it in your hand. But the same paper clip fired at the speed of a rifle bullet would have tremendous momentum, and you would not dare try to catch it. Momentum also depends on the mass of an object. Now imagine that, instead of tossing a paper clip, someone tosses you a bowling ball. A bowling ball contains much more mass than a paper clip and therefore has much greater momentum, even though it is moving at the same velocity.

Newton's second law

commonly written as F = ma. As always, you must define terms carefully when you look at an equation. An acceleration is a change in velocity, and a velocity is a directed speed. Most people use the words speed and velocity interchangeably, but they mean two different things. Speed is a rate of motion and does not have any direction associated with it, but velocity does. If you drive a car in a circle at 55 mph, your speed is constant, but your velocity is changing because your direction of motion is changing. An object experiences an acceleration if its speed changes or if its direction of motion changes. Every automobile has three accelerators—the gas pedal, the brake pedal, and the steering wheel. All three change the car's velocity. In a way, the second law is just common sense; you experience its consequences every day. The acceleration of a body is proportional to the force applied to it. If you push gently against a grocery cart, you expect a small acceleration. This law of motion also says that the acceleration depends on the mass of the body. If your grocery cart is filled with bricks and you push it gently, you expect very little result. If it is full of inflated balloons, however, it will move easily in response to a gentle push. Finally, the second law says that the resulting acceleration is in the direction of the force. This is also what you would expect. If you push on a cart that is not moving, you expect it to begin moving in the direction you push. This law of motion is important because it establishes a precise relationship between cause and effect. Objects do not just move. They accelerate due to the action of a force. Moving objects do not just stop. They decelerate due to a force. And moving objects don't just change direction for no reason. Any change in direction is a change in velocity and requires the presence of a force. Aristotle said that objects move because they have a tendency to move. Newton said that objects move due to a specific cause, a force.

Newton's third law of motion

specifies that for every action there is an equal and opposite reaction. In other words, forces must occur in pairs directed in opposite directions. For example, if you stand on a skateboard and jump forward, the skateboard will shoot away backward. As you jump, your feet must exert a force against the skateboard, which accelerates it toward the rear. But forces must occur in pairs, so the skateboard must exert an equal but opposite force on your feet, and that is what accelerates your body forward.

Newton and the Laws of Motion

three laws proposed by Isaac Newton to describe the motion of a body on which forces may act and which may exert forces on other bodies. From the work of Galileo, Kepler, and other early scientists, Isaac Newton was able to deduce three laws of motion that describe any moving object, from an automobile driving along a highway to galaxies colliding with each other. Those laws led Newton to an understanding of gravity. Newton's first law of motion is really a restatement of Galileo's law of inertia. An object continues at rest or in uniform motion in a straight line unless acted on by some force. Astronauts drifting in space will travel at constant rates in straight lines forever if no forces act on them. Newton's first law also explains why a projectile continues to move after all forces have been removed—for instance, how an arrow continues to move after leaving the bowstring. The object continues to move because it has momentum. You can think of an object's momentum as a measure of its amount of motion. An object's momentum is equal to its velocity times its mass. A paper clip tossed across a room has low velocity and therefore little momentum, and you could easily catch it in your hand. But the same paper clip fired at the speed of a rifle bullet would have tremendous momentum, and you would not dare try to catch it. Momentum also depends on the mass of an object. Now imagine that, instead of tossing a paper clip, someone tosses you a bowling ball. A bowling ball contains much more mass than a paper clip and therefore has much greater momentum, even though it is moving at the same velocity. Newton's second law of motion is about forces. Where Galileo spoke only of accelerations, Newton saw that an acceleration is the result of a force acting on a mass. Newton's second law is commonly written as F = ma. As always, you must define terms carefully when you look at an equation. An acceleration is a change in velocity, and a velocity is a directed speed. Most people use the words speed and velocity interchangeably, but they mean two different things. Speed is a rate of motion and does not have any direction associated with it, but velocity does. If you drive a car in a circle at 55 mph, your speed is constant, but your velocity is changing because your direction of motion is changing. An object experiences an acceleration if its speed changes or if its direction of motion changes. Every automobile has three accelerators—the gas pedal, the brake pedal, and the steering wheel. All three change the car's velocity. In a way, the second law is just common sense; you experience its consequences every day. The acceleration of a body is proportional to the force applied to it. If you push gently against a grocery cart, you expect a small acceleration. The second law of motion also says that the acceleration depends on the mass of the body. If your grocery cart is filled with bricks and you push it gently, you expect very little result. If it is full of inflated balloons, however, it will move easily in response to a gentle push. Finally, the second law says that the resulting acceleration is in the direction of the force. This is also what you would expect. If you push on a cart that is not moving, you expect it to begin moving in the direction you push. The second law of motion is important because it establishes a precise relationship between cause and effect. Objects do not just move. They accelerate due to the action of a force. Moving objects do not just stop. They decelerate due to a force. And moving objects don't just change direction for no reason. Any change in direction is a change in velocity and requires the presence of a force. Aristotle said that objects move because they have a tendency to move. Newton said that objects move due to a specific cause, a force. Newton's third law of motion specifies that for every action there is an equal and opposite reaction. In other words, forces must occur in pairs directed in opposite directions. For example, if you stand on a skateboard and jump forward, the skateboard will shoot away backward. As you jump, your feet must exert a force against the skateboard, which accelerates it toward the rear. But forces must occur in pairs, so the skateboard must exert an equal but opposite force on your feet, and that is what accelerates your body forward.