All posts tagged: dot physics

Drive Slower, Save Money on Gas. Thanks, Physics!

Drive Slower, Save Money on Gas. Thanks, Physics!

Published by skeptic

How much does your mileage vary with speed? Every car is different, but the US Department of Energy estimates that for every 5 mph increase in speed over 50 mph, fuel efficiency declines by 7 percent. In equation form: Courtesy of Rhett Allain Here e0 and v0 are the efficiency and velocity at some benchmark, and this tells you the efficiency for any other velocity. The 0.93 is that 7 percent decrease. Let’s do a quick example. Maybe your car gets 30 mpg (e0) at a speed of 70 mph (v0). Then at 75 mph it would get 27.9 mpg, and at 65 mph it would get 32.3 mpg. See how that works? Time and Money Now let’s pull this all together. If you drive faster, you save time. But you use more fuel, so it costs more. What are the terms of the trade-off? Let’s go back to our 30-mile trip, and I’ll assume gas costs $4 a gallon. If you drive at 70 mph with an efficiency of 30 mpg, you use 1 …

All the Fancy Measuring Devices Used in Science Rely on Two Stone-Age Techniques

All the Fancy Measuring Devices Used in Science Rely on Two Stone-Age Techniques

Published by skeptic

Humans are animals that measure things. Call us Homo mensura. We have a compulsion to quantify, and for millennia we’ve been inventing new ways to go about it. For anything you can think of, there’s a device to measure it—from sphygmomanometers to spectrophotofluorometers. And of course nowhere is this more true than in science. Well, science and baseball. Physicists build models to explain how the world works. It might be an equation, like the ideal gas law: PV = nRT. This tells us, for example, that if you double the temperature (T) of a gas, all else equal, its gas pressure (P) will double. But to see if the model is legit, or at least useful, we need to get some real-world values and check whether the equation holds. Modeling and measuring, measuring and modeling—that’s science in a nutshell. Of course, today we have some pretty fancy instruments for this. But I’m going to let you in on a little secret: With all of our cool tools, measurement still comes down to either comparison or …

Build a Radio Wave Detector With Balls of Aluminum Foil!

Build a Radio Wave Detector With Balls of Aluminum Foil!

Published by skeptic

The “Golden Age of Radio” supposedly ended in the ’50s, with the advent of television. But guess what? TV shows were broadcast with radio signals. And today? Radio is everywhere. You have a radio in your car, but maybe you prefer to stream music on your phone. Well, how does the music gets to you? Via radio waves from cell towers, is how. Your GPS runs on radio too. For that matter, so does your home Wi-Fi. Radio waves are a kind of electromagnetic radiation, just like visible light. But they’re at the bottom end of the spectrum, which makes them harmless to humans, because low frequency means low energy. (High-frequency, high-energy radiation like x-rays or gamma rays are another story.) That’s part of the reason radio waves are ideal for wireless communication. They can also travel vast distances and pass through obstacles like walls. So radio is as relevant as ever. But did you know you can easily build your own radio transmitter and receiver at home with some simple supplies? I’m going to …

Do Lightsaber Blades Have Mass?

Do Lightsaber Blades Have Mass?

Published by skeptic

When you think of Star Wars, you think of lightsabers. Right? What could be better, from a movie-making standpoint, than a futuristic sword that lets you create awesome fencing duels like in old-time Errol Flynn swashbucklers. (So much better than watching Stormtroopers fire their blasters into walls and ceilings and anything else except their targets.) Lightsabers come in a cosmic rainbow of hues (color-coded blue or green for good guys, red for bad) and a variety of shapes. There’s even a double-bladed version in Phantom Menace. (I don’t want to start a nerd fight—yet—but the best lightsaber battle in the canon has to be the “Duel of the Fates” in that movie, thanks to the skills and scariness of Darth Maul actor Ray Park.) So … exactly what are lightsabers? Of course, they aren’t real, so nobody really knows how they work. Even the characters in the movies seem a little confused about it. In Phantom Menace, Anakin calls it a “laser sword.” Yeah, he was a kid, but both Din Djarin (the Mandalorian) and …

How Can Astronauts Tell How Fast They’re Going?

How Can Astronauts Tell How Fast They’re Going?

Published by skeptic

Let’s use our car again, but this time we’ll get real numbers from the accelerometer in our smartphone. Say we start at a red light and then accelerate at 2 m/s2 (meters per second squared) for five seconds. From the equation above, Δv1 would be 2 x 5 = 10 m/s, so that’s our velocity. Now, after cruising for a while, we accelerate again at 1 m/s2 for five more seconds. Δv2 is then 1 x 5 = 5 m/s. Adding these two changes, our velocity is now 15 m/s. And so on. The only problem is that inertial measurement isn’t as accurate as the Doppler method over long periods, because small errors will keep accumulating. That means you need to recalibrate your system periodically using some other method. Optical Navigation On Earth, people have long navigated by the stars. In the northern hemisphere, just find Polaris. It’s called the North Star because Earth’s axis of rotation points right at it. That’s why it appears stationary, while the other stars seem to revolve around it. …

One Way or Another, Most of Our Electricity Comes From Solar Power

One Way or Another, Most of Our Electricity Comes From Solar Power

Published by skeptic

Get it? So a spinning loop produces an oscillating flux; if you graphed its values it would trace out a sine wave. That creates an oscillating voltage in the wire, causing electrons to move, and boom: You have alternating current. You just created a generator! This is called electric induction. Now you can amp this up by replacing that single loop of wire with a wrapped coil containing many, many loops. Oh, it also works in reverse: Instead of rotating a coil in a stationary magnetic field, you can rotate magnets around a stationary coil. The relative motion is all that matters. Putting a Spin on It So you see, almost all methods of generating electric power come down to a magnet and a coil of wire. We just need a way to rotate one or the other. For that we have some options. If you put big blades on your rotor and expose it to the wind, the collision of air particles on the blades exerts a torque and turns a shaft. That’s a …

You Can Approximate Pi by Dropping Needles on the Floor

You Can Approximate Pi by Dropping Needles on the Floor

Published by skeptic

Happy Pi Day! March 14 is the date that otherwise rational people celebrate this irrational number, because 3/14 contains the first three digits of pi. And hey, pi deserves a day. By definition, it’s the ratio of the circumference and diameter of a circle, but it shows up in all kinds of places that seem to have nothing to do with circles, from music to quantum mechanics. Pi is an infinitely long decimal number that never repeats. How do we know? Well, humans have calculated it to 314 trillion decimal places and didn’t reach the end. At that point, I’m inclined to accept it. I mean, NASA uses only the first 15 decimal places for navigating spacecraft, and that’s more than enough for earthly applications. The coolest thing, for me, is that there are many ways to approximate that value, which I’ve written about in the past. For instance, you can do it by oscillating a mass on a spring. But maybe the craziest method of all was proven in 1777 by George Louis Leclerc, …

How Can a Locomotive Pull a Long Train That’s Much Heavier?

How Can a Locomotive Pull a Long Train That’s Much Heavier?

Published by skeptic

The second difference is the equal sign instead of less-than-or-equal. This means the frictional force is constant as long as the object is sliding—it doesn’t equal the applied force anymore. That means the net force isn’t zero. Push harder on the chair by running and the chair will speed up. Let’s go back to that tug-of-war. The driver on the right now has an idea: Instead of gunning his engine, he throttles down to maintain a static friction interaction with the rails. Slow and steady. The guy on the left floors it—and what happens? His wheels spin and he gets a kinetic frictional force. Well, static friction beats kinetic friction, so the right train wins! This would work even if the train on the left is somewhat heavier. So, it is possible for a train engine to pull cars that are more massive. But wait! There’s an even more important factor: A moving train car is rolling, not sliding. The wheel just touches the rail at one point and then rolls on to another point …

Could AI Data Centers Be Moved to Outer Space?

Could AI Data Centers Be Moved to Outer Space?

Published by skeptic

Here ε is the emissivity of the object—how effective it is as a radiator (0 < ε < 1), σ is the Stefan-Boltzmann constant, A is the surface area, and T is the temperature (in Kelvin). Since we have temperature to the fourth power, you can see that hotter things radiate much more power than cooler things. OK, say you want to play Red Dead Redemption in space. Your computer is gonna get hot—maybe 200 F (366 Kelvin). To keep it simple, let’s say this is a cube-shaped PC with a total surface area of 1 square meter, and it’s a perfect radiator (ε = 1). The thermal radiation power would then be around 1,000 watts. Of course your computer is not a perfect radiator, but it looks like you’d be fine. As long as the output (1,000 watts) is greater than the input (300 watts), it’ll cool down. Now say you want to run some modest AI stuff. That’s a bigger job, so let’s scale up our cubical computer with edges twice as long …

How to Use Physics to Escape an Ice Bowl

How to Use Physics to Escape an Ice Bowl

Published by skeptic

I don’t know who invented this crazy challenge, but the idea is to put someone in a carved-out ice bowl and see if they can get out. Check it out! The bowl is shaped like the inside of a sphere, so the higher up the sides you go, the steeper it gets. If you think an icy sidewalk is slippery, try going uphill on an icy sidewalk. What do you do when faced with a problem like this? You build a physics model, of course. We’ll start with modeling how people walk on flat ground, and then we’ll apply it to a slippery slope. There are actually three possible escape plans, and I’ve used this model to generate animations so you can see how they work. So, first things first: How Do People Walk? When you shuffle from your front door to the mailbox, you probably don’t think about the mechanics involved. You solved that problem when you were a toddler, right? But this is what scientists do: We ask questions that nobody ever stopped …