UNIVERSAL GRAVITATION

Submitted To :

Mrs. Linimol.k.s Faculty in physical science department

Sreenarayana training college poochakkal

Submitted By :

Renju.R Option : Physical Science

Register Number : 18214383018 Submitted On : 7.9.2015

Isaac Newton

1643 - 1727

Newton & Physics

Newton’s Law of Universal Gravitation states that gravity is an attractive force acting between all pairs of massive objects.

Gravity depends on: Masses of the two objects Distance between the objects

Universal Gravitation

Universal Gravitation - Apple

Bottom LineGravity’s Inverse Square Law

Bottom Line

• Gravity is reduced as the inverse square of its distance from its source increased

• Fg ~ 1/r2•

Gravity’s Inverse Square Law

r 2r 3r 4r 5r 6r 60r

Fg Fg Fg Fg Fg Fg Fg

1 4 9 16 25 36 3600

Bottom LineGravity’s Inverse Square Law

Gravity decreases with altitude, since greater altitude means greater distance from the Earth's centre

If all other things being equal, on the top of Mount Everest (8,850 metres), weight decreases about 0.28%

Bottom LineGravity’s Inverse Square Law

Astronauts in orbit are NOT weightless

At an altitude of 400 km, a typical orbit of the Space Shuttle, gravity is still nearly 90% as strong as at the Earth's surface

Bottom LineLaw of Universal Gravitation

Newton’s discovery

Newton didn’t discover gravity. In stead, he discovered that the gravity is universal

Everything pulls everything in a beautifully simple way that involves only mass and distance

Bottom LineLaw of Universal Gravitation

Universal gravitation formula

Fg = G m1 m2 / d2

Fg: gravitational force between objectsG: universal gravitational constantm1: mass of one objectm2: mass of the other objectd: distance between their centers of

mass

Bottom LineLaw of Universal Gravitation

p.83

m1m2

d

Fg Fg

Fg Gm1m2

d 2

Bottom LineLaw of Universal Gravitation

Fg = G m1 m2 / d2

Gravity is always there

Though the gravity decreases rapidly with the distance, it never drop to zero

The gravitational influence of every object, however small or far, is exerted through all space

Bottom LineLaw of Universal Gravitation Example

Mass 1 Mass 2 Distance Relative Force

m1 m2 d F

2m1 m2 d

m1 3m2 d

2m1 3m2 d

m1 m2 2d

m1 m2 3d

2m1 2m2 2d

Law of Universal Gravitation Example

Mass 1 Mass 2 Distance Relative Force

m1 m2 D F

2m1 m2 d 2F

m1 3m2 d 3F

2m1 3m2 d 6F

m1 m2 2d F/4

m1 m2 3d F/9

2m1 2m2 2d F

Universal Gravitational Constant

The Universal Gravitational Constant (G) was first measured by Henry Cavendish 150 years after Newton’s discovery of universal gravitation

Henry Cavendish

1731 - 1810

Universal Gravitational Constant

Cavendish’s experiment

Use Torsion balance (Metal thread, 6-foot wooden rod and 2” diameter lead sphere) Two 12”, 350 lb lead spheres The reason why Cavendish measuring the G is to “Weight the Earth” The measurement is accurate to 1% and his data was lasting for a century

Cavendish’s Experiment

Universal Gravitational Constant

Universal Gravitational Force

Isaac Newton’s Influence

People could uncover the workings of the physical universe

Moons, planets, stars, and galaxies have such a beautifully simple rule to govern them

Phenomena of the world might also be described by equally simple and universal laws