Density of The Surrounding Medium
The greater the density of the surrounding medium, the stronger the force from dynamical friction. Similarly, the force is proportional to the square of the mass of the object. One of these terms is from the gravitational force between the object and the wake. The second term is because the more massive the object, the more matter will be pulled into the wake. The force is also proportional to the inverse square of the velocity. This means the fractional rate of energy loss drops rapidly at high velocities. Dynamical friction is, therefore, unimportant for objects that move relativistically, such as photons. This can be rationalized by realizing that the faster the object moves though the media, the less time there is for a wake to build up behind it.
Read more about this topic: Dynamical Friction
Famous quotes containing the words surrounding and/or medium:
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—Henry David Thoreau (1817–1862)
“A healthy soul stands united with the Just and the True, as the magnet arranges itself with the pole, so that he stands to all beholders like a transparent object betwixt them and the sun, and whoso journeys towards the sun, journeys towards that person. He is thus the medium of the highest influence to all who are not on the same level.”
—Ralph Waldo Emerson (1803–1882)