## Posts Tagged ‘physics’

### Double-Trouble Dominoes

April 6, 2021

Thought this was a great video of geometric growth in action by @uoftphysics Prof. Stephen Morris
https://www.youtube.com/watch?v=y97rBdSYbkg Starting with a ~5mm domino you get to a one ~1 m in size in 13 domino topples. Overall, this chain reaction represents a 2 billion-fold amplification!

QT:{{”
Dominoes are little toy rectangle tiles with dots on them. People like to stand them up on end in a long row, so when the first domino falls over, it knocks over the next domino, which knocks over the
next…pretty soon you have a rippling wave of falling dominoes. In this simple but amazing video, Stephen Morris shows that a little domino can knock over another one that’s 1 1/2 times as big in each direction. Then that one can tip over one that ‘s 1 1/2 times as big again. In this domino chain, the first one is only 1/4 inch tall, but the 13th domino weighs more than 100 pounds! If he kept going, the 29th domino would be as tall as the Empire State Building (1,454 feet). We’d all better get out of the way!
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### How to Calculate the String Angle of a Kite vs. a Balloon | WIRED

February 20, 2021

Great explanation of the physics!
https://www.wired.com/story/how-calculate-string-angle-kite-vs-balloon

### gravity – Would a light or a heavy ball roll fastest down a slope? – Physics Stack Exchange

January 28, 2017

http://physics.stackexchange.com/questions/19552/would-a-light-or-a-heavy-ball-roll-fastest-down-a-slope

QT:{{”

both balls should have same acceleration (and therefore same velocity and displacement).

However, if there’s air drag, their acceleration depends on the radius and the mass of the ball, so not enough information is given for this case. If the balls are of the same material (same density ρρ), the larger one comes down faster than the smaller one.
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### Sunday Puzzler: Rock the Boat http://www.slate.com/blogs/bad_astronomy/2016/06/26/if_you_throw_a_rock_off_a_boat_does_the_water_go_up_or_down.html

August 4, 2016

Puzzler: Rock the Boat
http://www.slate.com/blogs/bad_astronomy/2016/06/26/if_you_throw_a_rock_off_a_boat_does_the_water_go_up_or_down.html Good illustration of Archimedes’ principle & using extreme cases for intuition, ie dense rock

### Matter, energy… knowledge: How to harness physics’ demonic power | New Scientist

June 4, 2016

Matter, energy… knowledge: How to harness #physics’ demonic power
https://www.newscientist.com/article/mg23030730-200-demon-no-more-physics-most-elusive-entity-gives-up-its-secret/ Keeping memories costs energy, erasure does work

Emptying memory represents energy that can perform work

### Physics in finance: Trading at the speed of light : Nature News & Comment

April 3, 2015

#Physics in finance
http://www.nature.com/news/physics-in-finance-trading-at-the-speed-of-light-1.16872 Real estate opportunites from relativatistic arbitrage: locating exactly midway betw. market hubs

### The Long Road to Maxwell’s Equations – IEEE Spectrum

February 1, 2015

The Long Road to #Maxwell’s Equations
http://spectrum.ieee.org/telecom/wireless/the-long-road-to-maxwells-equations Heaviside simplified the original 20 eqns. to the current 4 w. vector fields

Also, Hertz’s 2 “loop” experiments were key!

A great grave to visit.

QT:{{”

Should you wish to pay homage to the great physicist James Clerk Maxwell, you wouldn’t lack for locales in which to do it. There’s a memorial marker in London’s Westminster Abbey, not far from Isaac Newton’s grave. A magnificent statue was recently installed in Edinburgh, near his birthplace. Or you can pay your respects at his final resting place near Castle Douglas, in southwestern Scotland, a short distance from his beloved ancestral estate.

You could start the clock in 1800, when physicist Alessandro Volta reported the invention of a battery, which allowed experimenters to begin working with continuous direct current. Some 20 years later,Hans Christian Ørsted obtained the first evidence of a link between electricity and magnetism, by demonstrating that the needle of a compass would move when brought close to a current-carrying wire. Soon after, André-Marie Ampère showed that two parallel current-carrying wires could be made to exhibit a mutual attraction or repulsion depending on the relative direction of the currents. And by the early 1830s, Michael Faraday had shown that just as electricity could influence the behavior of a magnet, a magnet could affect electricity, when he showed that drawing a magnet through a loop of wire could generate current.

A major seed was planted by Faraday, who envisioned a mysterious, invisible “electrotonic state” surrounding the magnet—what we would today call a field. He posited that changes in this electrotonic state are what cause electromagnetic phenomena.

The net result of all of this complexity is that when Maxwell’s theory made its debut, almost nobody was paying attention.

But a few people were. And one of them was Oliver Heaviside. Once described by a friend as a “first rate oddity,” Heaviside, who was raised in extreme poverty and was partially deaf, never attended university.

Heaviside ended up reproducing a result that had already been published by another British physicist, John Henry Poynting. But he kept pushing further, and in the process of working through the complicated vector calculus, he happened upon a way to reformulate Maxwell’s score of equations into the four we use today.

Now confident that he was generating and detecting electromagnetic waves, Lodge planned to report his astounding results at a meeting of the British Association, right after he returned from a vacation in the Alps. But while reading a journal on the train out of Liverpool, he discovered he’d been scooped. In the July 1888 issue of Annalen der Physik, he found an article entitled “Über elektrodynamische Wellen im Luftraum und deren Reflexion” (“On electrodynamic waves in air and their reflection”) written by a little-known German researcher, Heinrich Hertz.

Hertz’s … noticed that something curious happened when he discharged a capacitor through a loop of wire. An identical loop a short distance away developed arcs across its unconnected terminals. Hertz recognized that the sparks in the unconnected loop were caused by the reception of electromagnetic waves that had been generated by the loop with the discharging capacitor.

Inspired, Hertz used sparks in such loops to detect unseen
radio-frequency waves. He went on to conduct experiments to verify that electromagnetic waves exhibit lightlike behaviors of reflection, refraction, diffraction, and polarization.
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### Harvard Physics – Alumni Newsletter

November 27, 2014

QT:{{”
Dear Alumni,
I am delighted to announce the release of the first-ever Harvard University Department of Physics newsletter.
Whether you are near or far, we hope that this publication virtually brings you back to campus….
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