WHAT IS NASA PHYSICS?
MODULES
Forces and Motion
Conservation of Momentum & Energy
Temperature and Heat
Fluids
Optics
Electromagnetic Spectrum
Modern Physics
Anticipation Guide 7
Intro to Modern Physics
Blackbody Radiation
The Ultraviolet Catastrophe
The Photoelectric Effect
Bohr's Atom
Spectra
Radioactive Decay
Special Relativity (SR)
Simultaneity
Distance and Time
General Relativity
May the Forces be with You
Modern Physics Notebook
Assessment Problems 7
Useful Things
SITE MAP
Forces and Motion
Anticipation Guide
Speed and Velocity
Acceleration
Gravity
Projectile Motion
Orbital Motion
Newton's Laws of Motion
Assessment Problems
Equation
F_{g} = Gm_{1}m_{2}———r^{2}
1.10
Gravity
Universal Law of Gravity
Diagram from Pennsylvania Dept. of EducationThe force of gravity was first determined by Sir Isaac. He proposed that the force of gravity extends beyond the Earth and could even be responsible for holding the Moon in orbit. His Universal Law of Gravity states that every object in the universe attracts every other object with a force directed along the line of centers for the two objects that is proportional to the product of their masses and inversely proportional to the square of the separations between the two objects:
F_{g} = Gm_{1}m_{2}———r^{2}Here m_{1} and m_{2} are two masses such as the Earth and the Moon, r is the distance between them, and G is the universal gravitational constant = 6.67×10^{-11} Nm^{2}/kg^{2}
The force acting on each mass is equal: F_{1} = F_{2}
These units are unfamiliar. N stands for a Newton, which is the unit of force, being 1 kg*(m/s^{2}), so this constant is a Newton meter squared, for each kilogram squared.
This equation applies just as well on Earth as it does for distant galaxies, it is universal.
Planetary Gravity
While gravity is nearly the same across Earth it actually does have small variations that relate to the large scale geology of the Earth. NASA has launched a number of spacecraft missions to accurately measure gravity for Earth, the Moon and other planets to investigate the geology below ground that we can’t otherwise see. This map shows gravity anomalies – differences from the average – from the GRACE satellites (Gravity Recovery And Climate Experiment). The areas where gravity is strongest (shown in red) tend to be where plate tectonics activity is also strongest, for example, along the Andes Mountains.
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