# CHAPTER 13 - GRAVITATIONAL INTERACTIONS (collapsible outline, click on heading to expand), click on thumbnails for full sized images and diagrams

• from last chapter...

• Universal Law of Gravitation

Fg = G (m1m2) / r2

• GRAVITATIONAL FIELDS

• they are acceleration fields around objects with mass

• the strength of the field is proportional to the objects mass and inversely proportional to square of the distance from the center of mass (or center of gravity!!!)

• g= F/m = GM/R2

• GRAVITATIONAL FIELD INSIDE A PLANET

• g at the center of the Earth

• diving to the center of the earth

• WEIGHT and WEIGHTLESSNESS

• apparent weightlessness

• the 'Vomit Comet'

• OCEAN TIDES

"Tidal forces are based on the gravitational attractive force. With regard to tidal forces on the Earth, the distance between two objects usually is more critical than their masses. Tidal generating forces vary inversely as the cube of the distance from the tide generating object. Gravitational attractive forces only vary inversely to the square of the distance between the objects (Thurman, H.V., 1994). The effect of distance on tidal forces is seen in the relationship between the sun, the moon, and the Earth’s waters. Our sun is 27 million times larger than our moon. Based on its mass, the sun's gravitational attraction to the Earth is more than 177 times greater than that of the moon to the Earth. If tidal forces were based solely on comparative masses, the sun should have a tide-generating force that is 27 million times greater than that of the moon. However, the sun is 390 times further from the Earth than is the moon. Thus, its tide-generating force is reduced by 3903, or about 59 million times less than the moon. Because of these conditions, the sun’s tide-generating force is about half that of the moon (Thurman, H.V., 1994)."

source: NOAA Tides Page

•  • High Tide & Low Tide • Lunar Eclipses (Weds. night over most of North America)

Earth between the Sun and the Moon

• Spring Tides

When Earth, Moon, and Sun all line up

• Neap Tides

Moon & Sun 90° to each other

• EARTH TIDES and ATMOSPHERIC TIDES

• the not so solid Earth

mantle flows like oceans, very small movement (less than 1/2 meter)

the Ionosphere

• cosmic rays

• magnetic tides

• BLACK HOLES

• gravitation

• nuclear fusion

• can light escape

• can anything escape?

• SUMMARY   Copyright © 2005 -  S. B. EglI