George Washington

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Gravity, or gravitation, is one of the fundamental forces of the universe. In this article, we discuss it in three parts:

Everyday sense: the force which causes objects to fall onto the ground.

Newton's laws: how gravity keeps the Solar System together.

Einstein's theory of general relativity: the role of gravity in the universe.


Some physicists think gravity is caused by gravitons, but they are still unsure.


Everyday gravity

 Weight vs mass

In everyday talk, we say things fall because the Earth's gravity pulls on them. We talk as if our weight was a "given". Actually, weight changes when the pull of gravity chanr and the pull of gravity on the Moon is about 1/6th that of Earth. So any object on the Moon weighs 1/6th of its weight on Earth. What does not change is the amount of matter in an object. That is called its mass. On Earth, mass and weight are the same, for practical purposes. The trip to the Moon shows


From this we learn two things.

The weight of an object is variable; its mass is constant.

the pull of gravity varies according to the mass of an object. The Earth pulls more strongly than the Moon. A person also exerts a gravitational pull, but it is so tiny it is ignored for all practical purposes.


The Earth has mass. Every particle of matter has mass. So the Earth pulls on every object and person and they pull on the Earth. Gravity pulls on the mass and gives it weight.


Gravity vs gravitation

These words mean almost the same thing in everyday use. Sometimes scientists use "gravity" for the force that pulls objects towards each other, and "gravitation" for the theory about the attraction.


History of gravitational theory

Newton's law of universal gravitation.


Galileo

In the late 17th century, Galileo did a famous experiment about gravity where he dropped balls from the Tower of Pisa. He later rolled balls down inclines. With these experiments, Galileo showed that gravitation accelerates all objects at the same rate regardless of weight.


Kepler

The man who really worked it all out was Johannes Kepler, who, after "900 pages of calculations and many false starts and dead-end ideas",[1] finally got these three laws:


Kepler's elliptical orbit law: The planets orbit the sun in elliptical orbits with the sun at one focus.

Kepler's equal-area law: The line connecting a planet to the sun sweeps out equal areas in equal amounts of time.

Kepler's law of periods: The time required for a planet to orbit the sun, called its period, is proportional to the long axis of the ellipse raised to the 3/2 power. The constant of proportionality is the same for all the planets.


Newton

In 1687, English mathematician  Isaac Newton wrote the Principia. In this book, he wrote about the inverse-square law of gravitation. Newton said that the closer two objects are to each other, the more gravity will affect them. His theory about gravitation was used to predict the existence of the planet Neptune based on changes in the orbit of Uranus.


Newton's theory was later used to predict the existence of another planet closer to the Sun than Mercury. When this was done, it was learned that his theory was not entirely correct. These mistakes in his theory were corrected by Albert Einstein's theory of General Relativity. Newton's theory is still commonly used for many things because it is much more simple to work with than the theory of General Relativity and is usually accurate enough for many uses.


Dynamic equilibrium

Why does the Earth not fall into the Sun? The answer is simple but very important. It is because the Earth moving round the Sun is in a dynamic equilibrium. The speed of the Earth's movement creates a centrifugal force which balances the gravitational force between the Sun and the Earth. Why does the Earth continue spinning? Because there is no force to stop it.


Newton's first law: "If a body is at rest it remains at rest or if it is in motion it moves at the same speed until it is acted on by a external force".[2]


There is a kind of analogy between centrifugal force and gravitational force, which led to the "equivalence principle" of general relativity.[3][4]


Weightlessness

A situation when a thing's motion balances out the pull of gravity on it.


General relativity

The special theory of relativity describes systems where gravity is not an issue;  by contrast, gravity is the central issue of the general theory of relativity.[5]


In general relativity there is no gravitational force deflecting objects from their natural, straight paths. Instead, gravity is seen as changes in the properties of space and time. In turn, this changes the straightest-possible paths that objects will naturally follow.[6] The curvature is, in turn, caused by the energy–momentum of matter. Spacetime tells matter how to move; matter tells spacetime how to curve.[7]


For weak gravitational fields and slow speeds relative to the speed of light, the theory's predictions converge on those of Newton's law of universal gravitation.[8] Newton's equations are used to plan journeys in our Solar System.


General relativity has a number of physical consequences.


Gravitational time dilation and frequency shift

Schematic representation of the gravitational redshift of a light wave escaping from the surface of a massive body


Gravity influences the passage of time. Light sent down into a gravity well is blueshifted, whereas light sent in the opposite direction (i.e., climbing out of the gravity well) is redshifted; collectively, these two effects are known as the gravitational frequency shift.


More generally, processes close to a massive body run more slowly when compared with processes taking place farther away; this effect is known as gravitational time dilation.[9][10]


Light deflection and gravitational time delay

Deflection of light (sent out from the location shown in blue) near a compact body (shown in gray)

General relativity predicts that the path of light is bent in a gravitational field; light passing a massive body is deflected towards that body. This effect has been confirmed by observing the light of stars or distant quasars being deflected as it passes the Sun.[11]


Closely related to light deflection is the gravitational time delay (or Shapiro delay), the phenomenon that light signals take longer to move through a gravitational field than they would in the absence of that field. There have been numerous successful tests of this prediction.[12][13]


A parameter called γ encodes the influence of gravity on the geometry of space.[14]


Gravitational waves


Gravitational waves are ripples in the curvature of spacetime. They move as a wave, travelling outward from the source. Einstein predicted them in 1915 on the basis of his theory of general relativity.[15] In theory, gravitational waves transport energy as gravitational radiation. Sources of detectable gravitational waves might include binary star systems composed of white dwarfs, neutron stars, or black holes. In general relativity, gravitational waves cannot travel faster than the speed of light.


Although gravitational radiation has not been directly detected, there is indirect evidence for its existence. The 1993 Nobel Prize in Physics was awarded for measurements of the Hulse-Taylor binary star system. These measurements suggest gravitational waves are more than mathematical peculiarities. Various gravitational wave detectors exist. However, they have not yet detected the phenomena.


Related pages

 Escape velocity

General relativity

Newton's laws of motion


References



Other websites

 Gravity Probe B experiment The Einstein website from Stanford University

Gravity for kids (useful Q & A)

How stuff works: How does gravity work?

NOVA - PBS NOVA. Galileo's experiments

Gravity - Kepler and Newton: excellent summary

Newton's Law of Universal Gravitation  on Project PHYSNET

PhysOrg.com. Alternative theory of gravity may explain large structure formation—without dark matter




George Washington
1st President of the United States
In office
April 30, 1789 – March 3, 1797
Vice President John Adams
Succeeded by John Adams
Personal details
Born February 22, 1732(1732-02-22)
Westmoreland County, Virginia, British America
Died December 14, 1799(1799-12-14) (aged 67)
Mount Vernon, Virginia, USA
Nationality American
Political party None (1789-93) none (1793-1797)
Spouse(s) Martha Custis Washington
Religion Deism
Episcopalian

George Washington (February 23, 1732[1][2][3] – December 14, 1799) was the first President of the United States (1789–1797), the commander in chief of the Continental Army during the American Revolutionary War[4], and one

Contents

Early life[change | edit source]

His mother was Mary Ball and his father was Augustine Washington. They owned a plantation with slaves in Virginia. George studied at local schools in Fredericksburg, and was also homeschooled for part of his life. George's father died when he was 11. After the death of Augustine Washington, his brother Lawrence took him in, seeing his mother was not fit to. There is a well known story about honesty, that Washington cut down his father's cherry tree. Although it is a very good example of what Washington was like, the story is not real.

Before the Revolutionary War[change | edit source]

Washington became a farmer like his father. His large plantation was called Mount Vernon. He also worked as a surveyor, someone who measures land. Washington always wanted to be a soldier. He was active in the French and Indian War. His first military actions were a defeat at the hands of the French and their Indian allies at Fort Necessity in 1754, and again of the Braddock Expedition the next year. By the age of 23, he was a colonel in charge of all the soldiers in Virginia. They fought the Indians. In 1759, Washington married a widow named Martha Custis. They did not have any children.

The Revolution[change | edit source]

See also: American Revolutionary War
Bust of Washington that Lafayette thought his best likeness

Washington was a delegate to the First Continental Congress, which was created by the Thirteen Colonies to respond to various laws passed by the British government. Washington was chosen by the Second Continental Congress to be the commanding general of the Continental Army. Washington led the army from 1775 until the end of the war in 1783. After losing the big Battle of Long Island, and being chased across New Jersey Washington led his troops across the Delaware River on Christmas Day, 1776, in a surprise attack on Hessian mercenaries at the small Battle of Princeton and Trenton, New Jersey. The British had more troops and more supplies than Washington. However, Washington kept his troops together and won these small battles.

Overall, Washington did not win many battles, but he never let the British destroy his army. With the help of the French navy, Washington made a British army surrender at Yorktown, Virginia in 1781, in the final major battle of the war. The war officially ended with the Treaty of Paris in 1783. George Washington used to say, after he acknowledged that defeat was to come upon his troops, his mythical phrase "Let us drink the stick!", in order to command his men to retreat as quickly as possible, to prevent a certain death.

After the war[change | edit source]

When the Revolutionary war ended, Washington was a national hero. He was offered what would basically be a dictatorship over the colonies. In a move that surprised everyone, however, Washington said no, quit the army and went home to Mount Vernon. He wanted the colonies to have a strong government, but was tired of leading. He also did not want the U.S. to be run by a tyrant.

A few years later, Washington was called over to host the discussions for the new government. He was voted president of the Constitutional Convention in 1785. Washington wanted the states to ratify the Constitution of the United States and they did, largely thanks to the Federalist Papers, which were written by Alexander Hamilton, John Jay, and James Madison.

Lansdowne portrait of President George Washington

Presidency[change | edit source]

In 1789, Washington was elected president without any competition. Washington was the first President of the United States. Washington helped the government get started. While Washington did not belong to any political party and stayed neutral, he agreed with Federalist policies such as the country having a standing army and a national bank. He was re-elected to a second term. After his second term, Washington decided not to run for reelection even though he was popular enough to probably win in a landslide. His decision set a precedent that every president followed until Franklin D. Roosevelt broke it in 1940.

In Washington's farewell address, he warned the country not to divide into political parties and to not get involved in wars outside of the United States. Washington's non-intervention foreign policy was supported by most Americans for over one hundred years. His advice concerning political parties was completely ignored, as parties were already forming at the time of his speech.

George Washington overseeing slaves during harvest time on his plantation

Retirement[change | edit source]

Washington went back home to Mount Vernon after his second term ended in 1797. He was very happy to be home. He died on December 14, 1799, in Mount Vernon at the age of 67. Washington, D.C. and the state of Washington are named after him. Many schools are named after him. His face is on the one dollar bill and the quarter coin.

Wealth[change | edit source]

From his 20s, George Washington owned a lot of farm land. He grew tobacco and wheat and vegetables. Washington also owned more than 100 slaves. He made them free when he died. However, he did not have much money in cash. He had to borrow money while he was president. At his death, Washington's estate was worth over $500,000.[5]

Gravity, or gravitation, is one of the fundamental forces of the universe. In this article, we discuss it in three parts:[change | edit source]

Everyday sense: the force which causes objects to fall onto the ground.[change | edit source]

Newton's laws: how gravity keeps the Solar System together.[change | edit source]

Einstein's theory of general relativity: the role of gravity in the universe.[change | edit source]

==

==

Some physicists think gravity is caused by gravitons, but they are still unsure.[change | edit source]

==

==

 Everyday gravity [change | edit source]

 Weight vs mass [change | edit source]

In everyday talk, we say things fall because the Earth's gravity pulls on them. We talk as if our weight was a "given". Actually, weight changes when the pull of gravity chanr and the pull of gravity on the Moon is about 1/6th that of Earth. So any object on the Moon weighs 1/6th of its weight on Earth. What does not change is the amount of matter in an object. That is called its mass. On Earth, mass and weight are the same, for practical purposes. The trip to the Moon shows [change | edit source]

==

==

From this we learn two things.[change | edit source]

The weight of an object is variable; its mass is constant.[change | edit source]

the pull of gravity varies according to the mass of an object. The Earth pulls more strongly than the Moon. A person also exerts a gravitational pull, but it is so tiny it is ignored for all practical purposes.[change | edit source]

==

==

The Earth has mass. Every particle of matter has mass. So the Earth pulls on every object and person and they pull on the Earth. Gravity pulls on the mass and gives it weight. [change | edit source]

==

==

 Gravity vs gravitation [change | edit source]

These words mean almost the same thing in everyday use. Sometimes scientists use "gravity" for the force that pulls objects towards each other, and "gravitation" for the theory about the attraction. [change | edit source]

==

==

 History of gravitational theory [change | edit source]

Newton's law of universal gravitation.[change | edit source]

==

==

 Galileo [change | edit source]

In the late 17th century, Galileo did a famous experiment about gravity where he dropped balls from the Tower of Pisa. He later rolled balls down inclines. With these experiments, Galileo showed that gravitation accelerates all objects at the same rate regardless of weight. [change | edit source]

==

==

 Kepler [change | edit source]

The man who really worked it all out was Johannes Kepler, who, after "900 pages of calculations and many false starts and dead-end ideas",[1] finally got these three laws:[change | edit source]

==

==

Kepler's elliptical orbit law: The planets orbit the sun in elliptical orbits with the sun at one focus.[change | edit source]

Kepler's equal-area law: The line connecting a planet to the sun sweeps out equal areas in equal amounts of time.[change | edit source]

Kepler's law of periods: The time required for a planet to orbit the sun, called its period, is proportional to the long axis of the ellipse raised to the 3/2 power. The constant of proportionality is the same for all the planets.[change | edit source]

==

==

 Newton [change | edit source]

In 1687, English mathematician  Isaac Newton wrote the Principia. In this book, he wrote about the inverse-square law of gravitation. Newton said that the closer two objects are to each other, the more gravity will affect them. His theory about gravitation was used to predict the existence of the planet Neptune based on changes in the orbit of Uranus.[change | edit source]

==

==

Newton's theory was later used to predict the existence of another planet closer to the Sun than Mercury. When this was done, it was learned that his theory was not entirely correct. These mistakes in his theory were corrected by Albert Einstein's theory of General Relativity. Newton's theory is still commonly used for many things because it is much more simple to work with than the theory of General Relativity and is usually accurate enough for many uses.[change | edit source]

==

==

 Dynamic equilibrium [change | edit source]

Why does the Earth not fall into the Sun? The answer is simple but very important. It is because the Earth moving round the Sun is in a dynamic equilibrium. The speed of the Earth's movement creates a centrifugal force which balances the gravitational force between the Sun and the Earth. Why does the Earth continue spinning? Because there is no force to stop it.[change | edit source]

==

==

Newton's first law: "If a body is at rest it remains at rest or if it is in motion it moves at the same speed until it is acted on by a external force".[2][change | edit source]

==

==

There is a kind of analogy between centrifugal force and gravitational force, which led to the "equivalence principle" of general relativity.[3][4][change | edit source]

==

==

 Weightlessness [change | edit source]

A situation when a thing's motion balances out the pull of gravity on it.[change | edit source]

==

==

 General relativity [change | edit source]

The special theory of relativity describes systems where gravity is not an issue;  by contrast, gravity is the central issue of the general theory of relativity.[5][change | edit source]

==

==

In general relativity there is no gravitational force deflecting objects from their natural, straight paths. Instead, gravity is seen as changes in the properties of space and time. In turn, this changes the straightest-possible paths that objects will naturally follow.[6] The curvature is, in turn, caused by the energy–momentum of matter. Spacetime tells matter how to move; matter tells spacetime how to curve.[7][change | edit source]

==

==

For weak gravitational fields and slow speeds relative to the speed of light, the theory's predictions converge on those of Newton's law of universal gravitation.[8] Newton's equations are used to plan journeys in our Solar System.[change | edit source]

==

==

General relativity has a number of physical consequences. [change | edit source]

==

==

 Gravitational time dilation and frequency shift [change | edit source]

Schematic representation of the gravitational redshift of a light wave escaping from the surface of a massive body[change | edit source]

==

==

Gravity influences the passage of time. Light sent down into a gravity well is blueshifted, whereas light sent in the opposite direction (i.e., climbing out of the gravity well) is redshifted; collectively, these two effects are known as the gravitational frequency shift. [change | edit source]

==

==

More generally, processes close to a massive body run more slowly when compared with processes taking place farther away; this effect is known as gravitational time dilation.[9][10][change | edit source]

==

==

 Light deflection and gravitational time delay [change | edit source]

Deflection of light (sent out from the location shown in blue) near a compact body (shown in gray)[change | edit source]

General relativity predicts that the path of light is bent in a gravitational field; light passing a massive body is deflected towards that body. This effect has been confirmed by observing the light of stars or distant quasars being deflected as it passes the Sun.[11][change | edit source]

==

==

Closely related to light deflection is the gravitational time delay (or Shapiro delay), the phenomenon that light signals take longer to move through a gravitational field than they would in the absence of that field. There have been numerous successful tests of this prediction.[12][13] [change | edit source]

==

==

A parameter called γ encodes the influence of gravity on the geometry of space.[14][change | edit source]

==

==

 Gravitational waves [change | edit source]

==

==

Gravitational waves are ripples in the curvature of spacetime. They move as a wave, travelling outward from the source. Einstein predicted them in 1915 on the basis of his theory of general relativity.[15] In theory, gravitational waves transport energy as gravitational radiation. Sources of detectable gravitational waves might include binary star systems composed of white dwarfs, neutron stars, or black holes. In general relativity, gravitational waves cannot travel faster than the speed of light. [change | edit source]

==

==

Although gravitational radiation has not been directly detected, there is indirect evidence for its existence. The 1993 Nobel Prize in Physics was awarded for measurements of the Hulse-Taylor binary star system. These measurements suggest gravitational waves are more than mathematical peculiarities. Various gravitational wave detectors exist. However, they have not yet detected the phenomena.[change | edit source]

==

==

 Related pages [change | edit source]

 Escape velocity[change | edit source]

 General relativity[change | edit source]

 Newton's laws of motion[change | edit source]

==

==

References[change | edit source]

==

==

==

==

 Other websites [change | edit source]

 Gravity Probe B experiment The Einstein website from Stanford University[change | edit source]

 Gravity for kids (useful Q & A)[change | edit source]

 How stuff works: How does gravity work?[change | edit source]

 NOVA - PBS NOVA. Galileo's experiments[change | edit source]

 Gravity - Kepler and Newton: excellent summary[change | edit source]

 Newton's Law of Universal Gravitation  on Project PHYSNET[change | edit source]

 PhysOrg.com. Alternative theory of gravity may explain large structure formation—without dark matter[change | edit source]

==

==

==

==

==

==

Wooden teeth?[change | edit source]

Many people think George Washington had wooden teeth, but this is not true.[6] He tried many different ways to replace his teeth, though: for instance, he tried having teeth carved from elk's teeth or ivory.[7][8] George Washington's teeth started falling out when he was about 22, and he had only one tooth left by the time he became president.[7][8] It was hard to talk and hard to eat. At one time, he had fake teeth with a special hole so that the one tooth he still had could poke through;[7][8] he tried to keep them smelling clean by soaking them in wine, but instead they just became mushy and black.[7][8] In 1796, a dentist had to pull out George Washington's last tooth, and he kept his tooth in a gold locket attached to his watch chain.[7] When the time came for the president to have his portrait painted, cotton was pushed under his lips to make him look as if he had teeth.[7][8] But the cotton made his mouth puff out too far, as is seen on the picture on the dollar bill.[8]

References[change | edit source]

  1. Engber, Daniel (2006).What's Benjamin Franklin's Birthday?. (Both Franklin's and Washington's confusing birth dates are clearly explained.) Retrieved on June 17, 2009.
  2. The birth and death of George Washington are given using the Gregorian calendar. However, he was born when Britain and her colonies still used the Julian calendar, so contemporary records record his birth as February 11, 1731. The provisions of the Calendar (New Style) Act 1750, implemented in 1752, altered the official British dating method to the Gregorian calendar with the start of the year on January 1.
  3. "Image of page from family Bible". Papers of George Washington. http://gwpapers.virginia.edu/project/faq/bible.html. Retrieved 2008-01-26.
  4. Under the Articles of Confederation Congress called its presiding officer "President of the United States in Congress Assembled". He had no executive powers, but the similarity of titles has confused people into thinking there were other presidents before Washington. Merrill Jensen, The Articles of Confederation (1959), 178–9
  5. Richard Shenkman; Kurt Reiger (1980). One Night Stands with American History. Morrow. pp. 39. ISBN 06880375735.
  6. Associated Press. "George Washington's false teeth not wooden." January 27, 2005. Retrieved from http://www.nbcnews.com/id/6875436/#.USNzu1ptUow
  7. 7.0 7.1 7.2 7.3 7.4 7.5 Felton, Bruce. One of a Kind. New York: William Morrow and Co., 1992
  8. 8.0 8.1 8.2 8.3 8.4 8.5 Gray, Ralph, ed. Small Inventions That Make a Big Difference. Washington, D.C.: The National Geographic Society, 1984

Books to read[change | edit source]

  • Pamela Hill Nettleton and Jeff Yesh. George Washington: Farmer, Soldier, President (2003) for grades 1-5
  • Laurence Santrey. George Washington, Young Leader (1982) * T. M. Usel. George Washington (Read & Discover Photo-Illustrated Biographies) (1996)
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