Gravitational Theory

1609

Johannes Kepler demonstrated that Mars has an elliptical orbit.

1798

For the first time, Henry Cavendish measures the gravitational constant.

1846

Urbain Le Verrier, a French mathematician, uses Newton's laws to calculate the position of the planet Neptune.

1915

General relativity is first presented by Albert Einstein, who explains how the gravitational force depends on the curvature of spacetime.

2014

Atomic behavior is used to calculate the gravitational constant.

gravitational constant

Atomic behavior is used to calculate the ________.

Gravity

• The force of attraction between any two masses.

• It is the force that draws all objects to Earth and gives them mass.

• It pulls objects downward, toward the Earth's core.

Isaac Newton

an English physicist, astronomer, and mathematician, was the first to recognize gravity as a universal force acting on all objects and explaining the movement of planets.

Johannes Kepler

Based on the three laws of planetary motion established by ________, the shapes of the planets' orbits were already well known by the time of Isaac Newton.

First Law of Planetary Motion

Demonstrated that the orbits were ellipses as sun as their center.

Second Law of Planetary Motion

Stated that planets moved faster along their orbits when they were close to the sun than when they were farther away.

Third Law of Planetary Motion

Described the relationship between the time required to complete one orbit and the distance from the sun: the time required to complete one orbit, squared, was equal to the cube of the average distance between the planet and the sun.

Astronomia Nova (1609)

In Kepler’s book _________, he suggested that an angel driving a chariot was guiding Mars around its orbit.

Robert Hooke

Giovanni Alfonso Borelli

• They proposed the existence of a force of attraction between the sun and the various planets.

• They also claimed that as distance increased, the force diminished.

December 9, 1679

On _______, Hooke expressed his opinion in a letter to Newton that the force might decrease with the inverse square of distance.

Great Comet of 1680

The ________ was the brightest comet of the 17th century, shining so brilliantly that it was briefly visible during the day.

John Flamsteed

an astronomer, hypothesized that the two sightings might be of the same comet, which had come from the edge of the solar system, revolved around the sun, and then moved out again.

Philosophiae Naturalis Principia Mathematica

• Published in Latin on July 5, 1687.

• He explains his laws of motion, his theory of gravitation, how he proved Kepler's three laws, and how he calculated a comet's orbit.

• He emphasized that his law was universal—gravity affects everything in the universe, no matter how far away it is.

Gravitational Law

It states that the size of the gravitational force is proportional to the masses of the two bodies multiplied together and divided by the square of the distance between them

Gravitational Constant (G)

The constant of proportionality, a number that gives the strength of the force.

Henry Cavendish

In 1798, 71 years after Newton's death, _____ performed the first laboratory test of Newton's theory.

John Michell

Henry Cavendish replicated an experimental system proposed by geophysicist _____ and successfully measured the gravitational force between two lead balls with diameters of 2 and 12 in.

Tides

These are formed as a result of water bulging in both directions: away from the sun and moon on one side of Earth where their gravitational pull is stronger, and toward them on the other.

High Spring Tide

Occurs when the sun and moon are aligned.

Low Neap Tide

Occurs when the sun and moon are at right angles.