From what I understand, air gets thinner the further up you go. This I assume is because Earth’s gravity pulls all the heaviest particles down to its centre. I’m wondering about gravity itself though, is there a gradual shift in the strength of gravity as there is in the consistency of the air, or does gravity apply to the whole field surrounding the Earth up to the very perimeter and then quickly fall off?
In: 9
the strength of gravity depends on mass (direct variation) and distance (inverse square variation). This means if you double the mass, you double the strength, but if you double the distance of separation, the strength decreases by 4 (2×2; 2 squared) times.
Pressure is simply the weight of the overlying material that depends on its mass and distance from the center of gravity (really gets pulled in all directions but the pulls sum out to be as if the pull was at the center of the mass; less mass pulling up is weaker than more mass pulling down so the net (total) pull is down).
Gravity does vary because density varies. Density varies because different materials respond to pressure differently, some compress a lot (increase density a lot with pressure) and some do not at all. On top of all that, there is even a matter of the different masses of each element that comes into play and affects density (the same number of atoms per volume of a heavy element will have more mass, more weight, higher density than that of a lighter element).
Higher density has more mass so pulls harder than lower density. In the earth, the inside is made of (mostly) solids, but these solids have quite different densities depending on composition, pressure, temperature. So gravitational pull is slightly different depending on where you are and how those densities might differ from location to location. There are zones of “High” gravity and zones of “low” gravity if you measure total gravity to a very precise level.
The result is that sea level (the elevation above the center of the earth where gravity is constant and the same everywhere does change a bit, by a few meters to tens of meters, but the changes are gradual and cannot be seen by the naked eye (a few meters relative to the 6 million meter (6000 kilometer) distance to the center of the earth is not much at all), but it is there just the same.
Does gravity change? As already explained, yes it does over space (location), but it also does change over time, but only very slowly and only on the very tiny levels of some parts of a million over fairly large distances. These temporal (time-related) changes happen because the materials inside the earth do move around a bit and do cause density to change location. It is very slow.
Gravity is thought to be something that exists forever in space. It just becomes very very very weak with distance of separation. To cause a gravitational attraction a long distance away requires the existence of a huge mass.
It isn’t exactly a matter of heaviness so much as a matter of density (amount of mass per unit volume). Density is mostly a response to pressure (pressure makes the atoms tend to get closer together, so amount of mass per volume increases even when the individual atoms in the lower density and higher density zones are identical in composition and proportion). Temperature works in the opposite direction, making atoms try to move apart (keep bouncing into each other). Density is the concentration that results when the pushing together caused by pressure is balanced with the pushing apart caused by temperature.
Latest Answers