Oh, Hey! MinuteEarth! http://youtube.com/minuteearth .........and you can also subscribe to MinutePhysics! http://dft.ba/-minutephysics_sub
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A lot of people took pictures of the recent solar eclipse in North America and got photos where there’s a ghostly image of the eclipse floating in the sky nowhere near where the sun is!
REFERENCES:
Lens flare prediction based on measurements with real-time visualization https://doi.org/10.1007/s00371-018-1552-4
Physically-Based Real-Time Lens Flare Rendering http://doi.acm.org/10.1145/1964921.1965003
From the Series of Articles on Lens Names: Tessar, by H. H. Nasse. Carl Zeiss Camera Lens Division March 2011
https://www.cambridgeincolour.com/tutorials/lens-flare.htm
https://www.toolfarm.com/tutorial/in-depth-lens-flares-for-video/
https://petapixel.com/what-is-lens-flare/
https://www.maxon.net/en/red-giant/vfx-suite/real-lens-flares
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Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!
Created by Henry Reich
...
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MinutePhysics is on Google+ - http://bit.ly/qzEwc6
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Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!
Music by Nathaniel Schroeder http://www.soundcloud.com/drschroeder
...
https://www.youtube.com/watch?v=a0RFp1zib8g
Morally Wrong, that is...
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Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!
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This video is about the physics of geosynchronous and geostationary orbits, why they exist, when they don't, when they're useful for communication/satellite TV, etc.
REFERENCES
Fraction of a sphere that's visible from a given distance
https://math.stackexchange.com/questions/1329130/what-fraction-of-a-sphere-can-an-external-observer-see
Orbital period
https://en.wikipedia.org/wiki/Orbital_period
Kepler's third law
https://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion#Third_law
Kepler's 3rd law (which can be derived from Newton's law of gravitation and the centripetal force necessary for orbit as mr\omega^2=G\frac{mM}{r^2}, and using \omega=\frac{2\pi}{T}) is
T = 2pi Sqrt(r^3/(GM)) where M is the mass of the central object, G is the gravitational constant. Alternatively, we can solve for r, r = (T^2/(4pi^2) GM)^(1/3) ~ T^(2/3)/M^(1/3) = (T^2/M)^(1/3).
There is a limit (kind of like the Roche limit but for rotations). A rotating solid steel ball or other chunk of metal that has tensile strength (ie that isn't just a pile of stuff held together by gravity like most planets) would be able to spin faster.
Calculate how much of a planet's surface you can see from a given geosynchronous orbit/radius? (Obviously for lower ones you can see less, etc) - d/(2(R+d)) where d is distance to surface, ie, R is sphere radius, R+d is object radius from sphere center.
Let's plug that in with r being the geostationary orbit radius. That is, we have \frac{1}{2} \left(1- \left(\frac{4 \pi^2 R^3}{T^2 G M }\right)^{1/3}\right)
Average density of a sphere \rho is given by \rho =M/(\frac{4}{3}\pi R^3), ie \rho=\frac{3M}{4 \pi R^3} aka
\frac{M}{R^3}=\frac{4}{3}\pi \rho.
So we can convert the "fraction of planet surface seen" to
\frac{1}{2} \left(1- \left(\frac{3 \pi}{G \rho T^2}\right)^{1/3}\right)
So as either \rho or T\to \infty, the fraction goes to a maximum of \frac{1}{2}. And the point of "singularity" where the orbit coincides with the surface is where G\rho T^2=3\pi, aka \rho=\frac{3\pi}{GT^2}. For a rotation period of 3600s, that corresponds to a density \rho \approx 11000kg/m^3, which is roughly twice the density of the earth. For a rotation period of 5400s, we have \rho\approx 4800kg/m^3, which is basically the density of the earth.
Alternately, if we plug the density of the earth in to an orbit of period 5400s, we get as a fraction of the planet seen:
\frac{1}{2} \left(1- \left(\frac{3 \pi}{G \rho T^2}\right)^{1/3}\right) = 0.02
aka 2\% of the earth's surface.
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Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!
Created by Henry Reich
...
https://www.youtube.com/watch?v=tI8OqpkOVzs
Thanks to YouTube RED’s new original series, LIFELINE, for sponsoring this video. Watch the first episode for free: https://www.youtube.com/watch?v=Ru4zkxNuJ_I
And thanks to my friends Sam and Niko (and all the rest) at the Corridor Digital channel for making awesome videos.
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For ages I’ve been thinking about doing a video analyzing time travel in fiction and doing a comparison of different fictional time travels – some do use wormholes, some relativistic/faster than light travel with time dilation, some closed timelike curves, some have essentially “magic” or no consistent rules that make any sense, or TARDIS's, or whatever. This video is an explanation of how time travel functions in different popular movies, books, & shows – not how it works “under the hood", but how it causally affects the perspective of characters’ timelines (who has free will? can you change things by going back to the past or forwards into the future?). In particular, I explain Ender's Game, Planet of the Apes, Harry Potter and the Prisoner of Azkaban, Primer, Bill & Ted’s Excellent Adventure, Back to the Future, Groundhog Day, Looper, the video game “Braid”, and Lifeline.
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https://www.youtube.com/watch?v=d3zTfXvYZ9s
A million dollars is a ton of money. But how much does it weigh?
Trying out a new feature: English Transcript! Let me know how it works
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https://www.youtube.com/watch?v=-zexOIGlrFo
How is the chemical energy of gasoline transformed into kinetic energy of a moving car? And where does that kinetic energy go when the car crashes into something and stops moving?
Thanks to Ford (http://www.takeagoodlook.com) for sponsoring this video.
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How Einstein (& others) discovered Special Relativity.
Pi day (3.14) is Albert Einstein's Birthday! To celebrate, we'll explain 4 of his most groundbreaking papers from 1905, when he was just 26 years old.
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Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!
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