Slow Motion Gravity

Mike would you mind doing me a favor,

Keith Newton

Instead of posting the link in your text box, drop it in the "Optional Link URL" box just below it. This will make it SO MUCH EASIER for anybody viewing your link on a smart phone. My large fingers sometimes need three to four tries to get the right stuff highlighted.

Thank you brother. K

The Link *LINK*

Doc Green

Here ye go!


https://www.youtube.com/watch?v=duCZEooWSa4

Lenz's Law

John K Jordan

Tubalcain has a couple of videos about Lenz's Law.

https://www.youtube.com/watch?v=U3Dw_4GUYyk

https://www.youtube.com/watch?v=RU5RVQotz-o

I like the magnet sliding down the flat plate in the second video.

BTW, this guy is one of my favorites. A down-to-earth machinist, retired shop teacher, tinkerer.

I first saw this effect in the Exploratorium in San Francisco about 35 years ago.

JKJ

Re: Lenz's Law

mikeee12345

He does some really good videos on rebuilding metal lathes if anyone has the interest.

Re: Slow Motion Gravity

Don Stephan

I had learned that this was an Eddy Current. An understanding is more intuitive if the magnet is a cylinder, as most people may more easily associate north and south poles with a bar or cylinder than with a sphere.

My explanation was that when a magnet falls through a round conductor, each magnet pole induces an electric current in the conductor. And an electric current in turn induces a magnetic field. The induced magnetic field repels the lower pole of the falling magnet and attracts the upper pole, both working against the pull of gravity.

When I was trying to generate community interest in an Explortorium like science and math center here, this exhibit was extremey successful at catching and holding the attention of people of all ages, without any high technology mish mash.

The exhibit was several two foot long tubes, one plastic, one thick wall aluminum, and one thin wall aluminum mounted vertically, two cylindrical neodimium magnets and two similarly shaped wooden cylinders.

People easily understood the science behind the effect when this exhibit was positioned next to one with a DC motor wired to low voltage auto bulbs in series and parallel. A knob attached to a pulley allowed the visitor to turn the motor shaft, lighting the bulbs. Ideally this second exhibit would have had a second "cut away" dc motor showing the internal components, but almost everyone seemed to know that a motor consisted of a rotating magnet in a copper (conductor) coil.

One visitor who was studying aviation mechanics said an eddy current device was used to test for cracks in airplane fuselage, but connecting connectors to the fuselage and moving a magnet between them in a controlled fashion. when the conductors did not read a voltage it was felt there had to be a crack in the aluminum skin between them.

eddy currents

John K Jordan

When I worked in Nondestructive Testing in the nuclear industry in the 70s we used eddy currents, dye penetrant, magnetic particle, ultrasonics, and radiographic testing or a combination. Different materials, objects, specifications, and contracts specified what testing to use where. The most commonly used was radiographic testing but others were better at detecting delamination and some types of cracks and certain defects in certain materials.

Still fascinating after all these years.

JKJ

Yep pretty fascinating. But did you know?

Keith Newton

Here is the kind of weird knowledge that I've gained. This is probably something Galileo might have discovered if polycarbonate jars had existed when he dropped two spheres of different weights from the top of the Leaning Tower of Pisa.

Did you know that a almost full quart jar of mayonnaise lifted by the lid which is suppose to be screwed on, but isn't, appears to fall in slow motion from about 42" until it hits the floor. At the point of impact, rather than breaking like the older glass jars would have done, seem to expand from the gelatinous mass, somewhat like a water balloon. Then on the recoil, if the lid of the jar is at 90* to the direction of travel, it will then eject in that direction at the still slow same velocity and distance it has fallen, or perhaps further, unless there is another cabinet to impede its continuing.

Don't ask how I would come to possess this bit of extraneous knowledge, and I know it's hard to believe, you'll just have to do your own test to prove otherwise. 👹

Re: Yep pretty fascinating. But did you know?

John K Jordan

I'll give my wife your email address to explain what happened in the kitchen.

JKJ

I dropped a gallon of milk once.

john lucas

It went straight down. A spout of milk shot straight up about 4 feet and then went back down right into the neck spilling very little. I stood there in disbelief that it didn't just explode.

Re: Slow Motion Gravity

Bob Macgregor

Doesn't a magnetic brake use the same phenomenon, but with the magnet on the outside?

I remember a demonstration in a college physics class where a metal plate at the bottom end of a pendulum passed between two electromagnets. When the magnets were not energized, the plate swung through its normal arc. However, when the magnets were energized, the swinging plate stopped dead right between them.

Re: Slow Motion Gravity

John K Jordan

This is evidently a common technique.

I have a 40-year-old triple-beam Ohaus laboratory balance that has an aluminum vane on the end and magnets. The currents and fields induced by the magnets effectively dampen and stop the motion in seconds.

Hey, I think I'll an experiment with a strong magnet next to aluminum wheels on my bench grinder which will otherwise spin for minutes when I turn it off. That might beat stopping it with a wooden stick against the side.

JKJ

Re: Slow Motion Gravity

Bob Macgregor

I'm pretty sure the resistance on my recumbent exercise bike is provided via magnetic induction, too.