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Summary Notes on physics
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Summary of 2 pages for the course Phy 1124 at U of O (Notes on physics)
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Does the Earth Generate Gravitational Waves?● The Earth is a member of a complex multiple system of mutually interacting
objects, and is also rotating and asymmetric, with large regions of the Earth
being higher or lower than the average by tens of metres.
● The Earth's mantle is not uniform and large masses move slowly around so that
the Earth's pattern of asymmetry changes, producing gravitational waves.
PAGE 18
Does the Earth Generate Gravitational Waves Which We Can Detect?
● The smallest detectable strain in a test mass is around 1022, which is why
gravitational waves are so hard to detect.
● A detector needs to be at some distance from the source of its signal, so we
placed our detector on the exoplanet of the nearest star.
● A binary system like Earth-Moon would be too faint to be detected by current
detectors, and LISA would be sixteen orders of magnitude away from any
possible detections.
What About Making Our Own Detectable Gravitational Waves Then?
● Large centrifuges have been constructed by NASA and others to test spacecraft
and astronauts, but their gravitational wave emissions would be well outside
either AdvLIGO's or AdvVirgo's ranges. Perhaps we could link a couple of largish
boulders in space and set them spinning like roundabouts.
OK: Could the Earth/Sun/Solar System Be Affected Then?
● ''10 GW150914'' was one of the strongest gravitational wave events so far
observed. It changed the length of one of the 4 km long arms of AdvLIGO by just
0.25% of the diameter of a proton.
● Atoms in gases move 100 mm per second, so the gravitational waves will have
no significant macroscopic effects. The waves are also 3,000 km long, so if you
are 2 m in height, your whole body will experience almost exactly the same
displacement at the same instant.
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