Gravitational Interactions

Force Field- a magnetic field that exerts a a force on its objects in its vicinity
Gravitational field- Force field that surrounds massive objects
The strength of the earths gravitational fields the force per unit mass exerted by the earth on any object, g=f/m
near the surface of the earth , the gravitational field strength is , g= f/m=9.8 N/kg=9.8 m/s ^2
The value of g, g= f/m= gmM/R^2
G is a vector quantity, for it has both magnitude and direction


Gravitational Field inside a Planet


If you were to drill a hole through the earth, regardless of any of the logical problems which prevents us from doing this to begin with, the speed you would fall would be inconsistent. Coming from the North Pole going to the South Pole you would gain speed moving towards the center and loose speed falling away from the center. Without the air drag the entire trip would take nearly 45 minutes. The interesting thing about this trip is that if you failed to grab onto the edge while you were falling away from
grav_lens.jpg
A chart explaining a gravitational feild.


Weight and Weightlessness


The force of gravity causes acceleration. Gravity pulls objects to each other, which is why we are pulled to the earth. The pressure between a human and the earth defined by gravity is called weight. By Newtons third law, if you stand on a scale in the bathroom it pushes upwards on you. The springs within the scale are compressed with this pair of forces, and the reading is linked to the compression on the scale. If you were to preform this same act on an elevator your results would vary significantly. By accelerating upwards the springs in the scale push harder on your feet and it would mesure an increase in your weight. The same rule applys to going downward in an elevator , which would show a decrease in your weight. If the elevator cord broke the scale would read that you are weightless and you would feel that way as well.
The concept of weightlessness is not the absense of gravity but rather its the absense of support force.
weightless.jpg
It is a common misconception that the idea of " weightlessness" can be experienced in space.



Ocean Tides


Newton showed that titdes are caused by differences in the gravitational pull of the moon on opposite sides of the earth. The moons attraction is stronger on the earths oceans closer to the moon, and weaker on the oceans farther from the moon. This is because the gravitational force is weaker with increased distance. The moons pull is stronger on the ocean nearer to the moon and weaker on the opposite ocean farther away.The earth is orbiting around the moon, just as the moon is orbiting around the earth. They are both circling around their combined centers of mass. A combined center of mass is a point inside the earth about three quarters of the way from the earth's center to its surface. The ocean nearest to the moon is pulled upward towards the moon, while the main body of the earth is pulled towards the moon as well, away from the ocean on the far side. This causes the earths water to get slightly elongated at both ends. The earth makes one complete turn per day beneath ocean bulges. This produces two sets of ocean tides per day. At any given time that part of the earth that passes. Worldwide, the average high tide is about 1 meter above the average surface level of the ocean.

tides.jpg
Here is an example of the tides and the difference in water levels.

Here is an example of the changing tides and the difference in water levels.


Tides in the Earth and Atmosphere

The earth is mostly covered by a thin solid and pliable crust. The moon-sun tidal forces produce earth tides as well as ocean tides twice a day. Within these two times the earth rises and falls as much as 25 cm but it goes undetectable by most people. We have satellite detectors to measure both ocean and earth tidal movements. It is more likely that an earthquake or volcanic eruption would happen during the spring tide is near a full or new moon. Just as the like fish live in a world of water, we live in a world of oxygen and experience atmospheric tides which are relatively small. The upper part of the atmosphere is the ionosphere which is named that because its made up of ions (electrically charged atoms that are the result of intense cosmic ray bombardment and ultraviolet radiation from the sun). Tidal effects on the ionosphere produce electric currents that alter the magnetic field that surrounds the earth. These are magnetic tides. They in turn regulate the degree to which cosmic rays penetrate into the lower atmosphere. These penetrations effect the ionic composition of our atmosphere, which has subtle changes in living things. Spring tides create the highest of highs and lowest of lows of magnetic tides .

tide-tables-a-2.jpg

Above is a picture chart of the reasoning of tides.

Black Holes


There are two process going on in our stars continual. The first process is gravitation, which crunches all solar material into the center. The other process is called thermonuclear fusion consisting of reactions similar to those in a hydrogen bomb, which tend to blow material outward. When these two processes balance each other out, the result is the sun of a given size. If the fusion rate increases, the result will create a hotter and bigger sun. Now if the fusion rate was to decrease, naturally the sun will get smaller and cooler. When the sun runs out of hydrogen(or fusion fuel) gravitation will take over and the sun will eventually collapse. For our own sun the collapse will ignite nuclear ashes of helium and fuse them into carbon. Thus a red giant is born, as the sun expands during this fusion process. When the helium is all burned out the red giant will collapse and die in time, and all the light and heat will cease and will be known as a black dwarf. In some situations with stars more massive than the sun it doesnt only collapse but the atoms collapse and there are no empty spaces. The goes on infinitively the collapse never stops and the gravitational becomes so huge that nothing can get out! Even light cannot escape and this is what we call a black hole.


external image moz-screenshot-1.jpgexternal image moz-screenshot-2.jpgblack-hole-size-horizontal.jpg
It is questioned just how big these " massive" black holes really are, the chart above gives a better understanding.
black-hole-stifle-stars.jpg
One artists interpretation of a black hole.