You Are Already Traveling At The Speed Of Light

March 10, 2025 by Al Williams 40 Comments

Science fiction authors and readers dream of travelling at the speed of light, but Einstein tells us we can’t. You might think that’s an arbitrary rule, but [FloatHeadPhysics] shows a different way to think about it. Based on a book he’s been reading, “Relativity Visualized,” he provides a graphic argument for relativity that you can see in the video below.

The argument starts off by explaining how a three-dimensional object might appear in a two-dimensional world. In this world, everything is climbing in the hidden height dimension at the exact same speed.

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Building An Interferometer With LEGO

February 28, 2025 by Lewin Day 14 Comments

LEGO! It’s a fun toy that is popular around the world. What you may not realize is that it’s also made to incredibly high standards. As it turns out, the humble building blocks are good enough to build a interferometer if you’re so inclined to want one. [Kyra Cole] shows us how it’s done.

The build in question is a Michelson interferometer; [Kyra] was inspired to build it based on earlier work by the myphotonics project. She was able to assemble holders for mirrors and a laser, as well as a mount for a beamsplitter, and then put it all together on a LEGO baseboard. While some non-LEGO rubber bands were used in some areas, ultimately, adjustment was performed with LEGO Technic gears.

Not only was the LEGO interferometer able to generate a proper interference pattern, [Kyra] then went one step further. A Raspberry Pi was rigged up with a camera and some code to analyze the interference patterns automatically. [Kyra] notes that using genuine bricks was key to her success. Their high level of dimensional accuracy made it much easier to achieve her end goal. Sloppily-built knock-off bricks may have made the build much more frustrating to complete.

We don’t feature a ton of interferometer hacks around these parts. However, if you’re a big physics head, you might enjoy our 2021 article on the LIGO observatory. If you’re cooking up your own physics experiments at home, don’t hesitate to drop us a line!

Thanks to [Peter Quinn] for the tip!

Is Fire Conductive Enough To Power A Lamp?

February 2, 2025 by Maya Posch 17 Comments

Is fire conductive? As ridiculous that may sound at first glance, from a physics perspective the rapid oxidation process we call ‘fire’ produces a lot of substances that can reduce the electrical insulating (dielectric) properties of air. Is this change enough to allow for significant current to pass? To test this, [The Action Lab] on YouTube ran some experiments after being called out on this apparent fact in the comments to an earlier video.

Ultimately what you need to make ‘fire’ conductive is to have an appreciable amount of plasma to reduce the dielectric constant, which means that you cannot just use any rapid oxidation process. In the demonstration with lights and what appears to be a (relatively clean-burning) butane torch, the current conducted is not enough to light up an incandescent or LED light bulb, but can light up a 5 mm LED. When using his arm as a de-facto sensor, it does not conduct enough current to be noticeable.

The more interesting experiment here demonstrates the difference in dielectric breakdown of air at different temperatures. As the dielectric constant for hot air is much lower than for room temperature air, even a clean burning torch is enough to register on a multimeter. Ultimately this seems to be the biggest hazard with fire around exposed (HV) electrical systems, as the ionic density of most types of fire just isn’t high enough.

To reliably strike a conductive plasma arc, you’d need something like explosive (copper) wire and a few thousand joules to pump through it.

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Turns Out Humans Are Terrible At Intuiting Knot Strength

January 6, 2025 by Donald Papp 36 Comments

We are deeply intuitively familiar with our everyday physical world, so it was perhaps a bit of a surprise when researchers discovered a blind spot in our intuitive physical reasoning: it seems humans are oddly terrible at judging knot strength.

One example is the reef knot (top) vs. the grief knot (bottom). One is considerably stronger than the other.

What does this mean, exactly? According to researchers, people were consistently unable to tell when presented with different knots in simple applications and asked which knot was stronger or weaker. This failure isn’t because people couldn’t see the knots clearly, either. Each knot’s structure and topology was made abundantly clear (participants were able to match knots to their schematics accurately) so it’s not a failure to grasp the knot’s structure, it’s just judging a knot’s relative strength that seems to float around in some kind of blind spot.

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Pulling Backward To Go Forward: The Brennan Torpedo Explained

December 17, 2024 by Donald Papp 17 Comments

The Brennan torpedo, invented in 1877 by Louis Brennan, was one of the first (if not the first) guided torpedoes of a practical design. Amazingly, it had no internal power source but it did have a very clever and counter-intuitive mode of operation: a cable was pulled backward to propel the torpedo forward.

If the idea of sending something forward by pulling a cable backward seems unusual, you’re not alone. How can something go forward faster than it’s being pulled backward? That’s what led [Steve Mould] to examine the whole concept in more detail in a video in a collaboration with [Derek Muller] of Veritasium, who highlights some ways in which the physics can be non-intuitive, just as with a craft that successfully sails downwind faster than the wind.

The short answer is gearing, producing more force on the propeller by pulling out lots of rope.

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The Stern-Gerlach Experiment Misunderstood

December 13, 2024 by Al Williams 15 Comments

Two guys — Stern and Gerlach — did an experiment in 1922. They wanted to measure magnetism caused by electron orbits. At the time, they didn’t know about particles having angular momentum due to spin. So — as explained by [The Science Asylum] in the video below — they clearly showed quantum spin, they just didn’t know it and Physics didn’t catch on for many years.

The experiment was fairly simple. They heated a piece of silver foil to cause atoms to stream out through a tiny pinhole. The choice of silver was because it was a simple material that had a single electron in its outer shell. An external magnet then pulls silver atoms into a different position before it hits some film and that position depends on its magnetic field.

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Intuition About Maxwell’s Equations

November 13, 2024 by Al Williams 13 Comments

You don’t have to know how a car engine works to drive a car — but you can bet all the drivers in the Indy 500 have a better than average understanding of what’s going on under the hood. All of our understanding of electronics hinges on Maxwell’s equations, but not many people know them. Even fewer have an intuitive feel for the equations, and [Ali] wants to help you with that. Of course, Maxwell’s gets into some hairy math, but [Ali] covers each law in a very pragmatic way, as you can see in the video below.

While the video explains the math simply, you’ll get more out of it if you understand vectors and derivatives. But even if you don’t, the explanations provide a lot of practical understanding

Understanding the divergence and curl operators is one key to Maxwell’s equations. While this video does give a quick explanation, [3Blue1Brown] has a very detailed video on just that topic. It also touches on Maxwell’s equations if you want some reinforcement and pretty graphics.

Maxwell’s equations can be very artistic. This is one of those topics where math, science, art, and history all blend together.

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