MinutePhysics: Recent Episodes
MinutePhysics
Simply put: cool physics and other sweet science. https://www.patreon.com/minutephysics https://twitter.com/minutephysics https://www.facebook.com/MinutePhysics https://www.youtube.com/c/minutephysics "If you can't explain it simply, you don't understand it well enough." ~Rutherford via Einstein? (wikiquote)
Solar eclipses don't just happen here on earth - moons of other planets also pass between those planets and the sun, resulting in various types of solar eclipses on Mars, Jupiter, Saturn, Uranus, Neptune, and even non-planets like Pluto, Eris and various asteroids. So, where are the best eclipses in the solar system? For that, we need a tier list.
This Product is supported by the NASA Heliophysics Education Activation Team (NASA HEAT), part of NASA’s Science Activation portfolio.
The material contained in this document is based upon work supported by a National Aeronautics And Space Administration (NASA) grant or cooperative agreement. Any questions, findings, conclusions or recommendations expressed in this materials are those of the author and do not necessarily reflect the views of NASA.
Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics
Link to Patreon Supporters: http://www.minutephysics.com/supporters/
MinutePhysics is on twitter - @minutephysics
And facebook - http://facebook.com/minutephysics
Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!
Created by Henry Reich
The sun rises in the east, the moon rises in the east, and the stars rise in the east... but solar eclipses, oddly, come from the west. If total eclipses are caused by the sun and the moon, why don't they behave like the sun and the moon?
This Product is supported by the NASA Heliophysics Education Activation Team (NASA HEAT), part of NASA’s Science Activation portfolio.
The material contained in this document is based upon work supported by a National Aeronautics And Space Administration (NASA) grant or cooperative agreement. Any questions, findings, conclusions or recommendations expressed in this materials are those of the author and do not necessarily reflect the views of NASA.
Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics
Link to Patreon Supporters: http://www.minutephysics.com/supporters/
MinutePhysics is on twitter - @minutephysics
And facebook - http://facebook.com/minutephysics
Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!
Created by Henry Reich
The moon orbits the earth once per month, which means the moon is on the sun side of the earth every month. So... "why aren't there eclipses every month?" is a question we will answer in this video!
This Product is supported by the NASA Heliophysics Education Activation Team (NASA HEAT), part of NASA’s Science Activation portfolio.
The material contained in this document is based upon work supported by a National Aeronautics And Space Administration (NASA) grant or cooperative agreement. Any questions, findings, conclusions or recommendations expressed in this materials are those of the author and do not necessarily reflect the views of NASA.
Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics
Link to Patreon Supporters: http://www.minutephysics.com/supporters/
MinutePhysics is on twitter - @minutephysics
And facebook - http://facebook.com/minutephysics
Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!
Created by Henry Reich
Want to donate to the highest-impact charities AND get your donation matched up to $100? Visit https://Givewell.org/MinutePhysics
If you’re in scorching heat, or when your body is working hard and you’ve got hot, hot sweat all over, sticky and stifling - does wiping off the sweat help you cool off? Or is it better to leave it on?
Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics
Link to Patreon Supporters: http://www.minutephysics.com/supporters/
REFERENCES
Hyperphysics:
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/sweat.html
Engineering Toolbox Mollier Diagram:
http://www.engineeringtoolbox.com/psychrometric-chart-mollier-d_27.html
Sweat Info
http://www.anaesthesiamcq.com/FluidBook/fl3_3.php
Other articles:
http://www.slate.com/articles/health_and_science/explainer/2012/06/should_you_wipe_away_your_sweat_or_does_that_keep_you_from_cooling_down_.html
http://onlinelibrary.wiley.com/doi/10.1111/j.1748-1716.2012.02452.x/abstract
http://lifehacker.com/5921036/dont-wipe-your-sweat-off-your-brow-itll-cool-you-down-faster
http://www.realclearscience.com/2012/06/28/does_wiping_sweat_prevent_you_from_cooling_off_247729.html
CALCULATIONS
Typical adult human body surface area ~ 1.5-2 m^2
https://en.wikipedia.org/wiki/Body_surface_area
Evaporation rate at 25°C and 50% humidity, slight air movement (v~.5m/s) = .35kg/m^2/hr
http://www.engineeringtoolbox.com/evaporation-water-surface-d_690.html
So in these conditions, a sweat-covered human can expect to evaporate ~.5-.75 L of water in an hour (For higher humidity (60-70%) it goes to ~.37-.5 L of water/hr). That amounts to ~0.25-0.35mm of sweat (covering the whole body) evaporated in an hour, or 6 micrometers every minute.
Water has latent heat of 2,270 kJ/kg (http://www.engineeringtoolbox.com/water-thermal-properties-d_162.html), so in an hour a human can lose ~1100-1700 kJ of energy. (2270/4.1868 ~ 542 Cal)
BUT that assumes all of the energy came from the person. If some proportion of it came from the air (~1/3-1/2?) then the person is only cooled down partially.
Mass of a human ~ 60-80kg (https://en.wikipedia.org/wiki/Body_weight), assuming ~specific heat of water, ie 4 kJ/kg/K, could decrease temp by ~4.5-5°C.
Energy used in moderate-hard exercise is ~20-30 kJ/kg/30 min, or ~40-60kJ/kg/h (http://www.weightloss.com.au/weight-loss/weight-loss-tools/exercise-energy-charts.html). Let’s say 50kJ/kg/h, which for average human amounts to 3000-4000 kJ/hr
MinutePhysics is on twitter - @minutephysics
And facebook - http://facebook.com/minutephysics
Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!
Created by Henry Reich
This video is supported by the NASA Heliophysics Education Activation Team (NASA HEAT), part of NASA’s Science Activation portfolio.
We are in the Golden Age of Solar Eclipses, but only for the moment. In fact, I'd argue we're already past peak solar eclipse and it's all downhill from here.
Support MinutePhysics on Patreon! https://www.patreon.com/minutephysics
Link to Patreon Supporters: https://www.minutephysics.com/supporters/
MinutePhysics is on twitter - @minutephysics
And facebook - https://facebook.com/minutephysics
Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!
Created by Henry Reich
Sign up for Brilliant (for free) and get 30 days of full access to all of their courses, go to https://brilliant.org/MinutePhysics - The first 200 people get 20% off a premium subscription!
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
Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics
Link to Patreon Supporters: http://www.minutephysics.com/supporters/
MinutePhysics is on twitter - @minutephysics
And facebook - http://facebook.com/minutephysics
Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!
Created by Henry Reich
The first 200 people to go to http://brilliant.org get 20% off a premium subscription! I was sent a magnetic guitar pick to review, so I reviewed it. Does it work? How? Why? What's the physics of electric guitar strings and pickups? Are magnets ...
Go to https://givewell.org/minutephysics to have your first donation matched up to $100!
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's_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.
Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics
Link to Patreon Supporters: http://www.minutephysics.com/supporters/
MinutePhysics is on twitter - @minutephysics
And facebook - http://facebook.com/minutephysics
Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!
Created by Henry Reich
The first 200 people to https://brilliant.org/minutephysics get 20% off an annual premium subscription to Brilliant. Thanks to Brilliant for their support. This video is about a better way to understand Penrose tilings (the famous tilings invente...
The first 200 people to https://brilliant.org/minutephysics get 20% off an annual premium subscription to Brilliant. Thanks to Brilliant for their support. Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Su...
Where to buy WHAT IF? 2 by Randall Munroe – Amazon: https://bit.ly/3Rk5Vy2 Barnes and Noble: https://bit.ly/3AKwXIl Penguin Random House: https://bit.ly/3HgfucP Books-A-Million: https://bit.ly/3Q4bEH3 Bookshop: https://bit.ly/3q...
Nebula Classes - Great classes by your favorite creators on a creator-owned streaming service: https://nebulaclasses.com/minutephysics This video is about what happens if you try to pass a portal (like in the video game Portal or Portal 2) throug...
A beautiful guest video by Robert Krulwich and Nate Milton Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysic...
We have a course on Brilliant! And the first 200 people to https://brilliant.org/minutephysics get 20% off an annual premium subscription to Brilliant, with full access to all courses, including ours. What happens if you extend a piston through ...