Sorry, Sandra Bullock: A Fire Extinguisher Is a Lousy Thruster

Suppose you are an astronaut out in space. You have nothing with you except your wits and … a fire extinguisher? Why a fire extinguisher? Because that’s what Sandra Bullock’s character has in the movie Gravity. Because a fire extinguisher shoots out gas (normally to put out a fire), it can also be used to produce thrust and help you maneuver in space. But would this really work? That is what the MythBusters, for whom I’m a science consultant, set out to test in a recent episode.

The MythBusters started by trying to create a similar situation on the surface of the Earth. They used a leaf blower to fashion a one-person hovercraft (it’s not too hard to build one yourself). They let it loose on an ice rink, which pretty much eliminated the frictional force. Then they used a fire extinguisher for thrust and tried maneuvering around on the ice.

It turned out that the fire extinguisher wasn’t so great for controlling the motion of the hovercraft. [...]  read more

How to Figure Out a Drone’s Angular Field of View

You know what happens when I get a new toy? Physics happens. I can’t stop myself, it’s just the way I am.

In this case, the toy is a DJI Spark drone (it was a birthday present). I’ve always wanted a drone that could do some cool stuff. The one I had before was basically just a toy. But with this new toy, I am going to determine the angular field of view for the Spark camera.

Sometimes referred to as FOV, the angular field of view is the portion of the world that a camera can see.

Here, maybe this picture will help.

Rhett Allain

Anything within that angle (θ) can be seen by the camera. Who cares? If you know the FOV, you can get the angular size of objects that you see. Angular size depends on both the distance from the camera and the size of the object. If you measure the angular size in radians, then the following relationship holds.

Rhett Allain

In this expression, r is the distance to the object and L is the length of the object. But here’s the real [...]  read more

The Way Superman Picks Up a Building Is a Physics Travesty

You can’t really use standard physics principles to explain how Superman can be so strong or fly or have x-ray vision. Pretty much everything he does is impossible. But hey—that’s OK. I’m fine with this stretching of reality. It’s what makes superheroes interesting. They don’t have to be completely realistic to be entertaining.

But sometimes things just cross the line for me. Let’s take a look at a scene from Justice League (the movie). Don’t worry about all the details (also because I don’t want to spoil the plot), but at some point Flash and Superman are trying to save a bunch of people in a town that is going to get destroyed. Flash, being the Flash, ends up pushing a pickup truck with some people in it. He goes super fast and they reach safety. Yay! Oh but wait. Superman is better. Instead of saving just a couple of people, he flies out of town carrying a whole building.

This is where I have a problem. I don’t [...]  read more

This Fearsome *Titan Games* Event Reveals the Value of Torque

I’m oddly attracted to The Titan Games. I think we can all agree that this is the newest incarnation of the popular ’90s show American Gladiators. It’s not the theatrics that I enjoy, it’s the crazy competitions. As you can imagine, there’s a bunch of cool physics to talk about for some of these events. Actually, if you use a little bit of physics you might be able to get an advantage over your opponent.

In this case, the event is the Herculean Pull. The main idea is to pull some horizontal poles out of a giant wedge. The two contestants are trying to pull the poles out from different sides. There’s a chance you could reach a pole before the other person and win the easy way. But if you’re both pulling on the same pole, you need to use some physics. Here, check out this clip from the show.


p class=”paywall”>The physics trick is to not just pull out on the pole—but also UP! Yes, pull out and up. This is especially true if you are [...]  read more

Thank the Old-Timey Telegraph for Your Garage Door Opener

I remember the first time I had to deal with a faulty relay. My garage door opener had stopped working, and my kids were tired of going out in the rain to open the garage door manually (it’s my job as the dad to control the car). It turned out that our 20-year-old opener had a bad relay.

But what the heck is a relay? How do they work? Why do you need one? Yes, I am going to answer these questions for you.

It appears that the first relays were created for the telegraph system. A telegraph is a fairly simple technology. Essentially, it’s a battery and a switch on one end and an electromagnet on the other end. When a human presses the switch at the transmitting side of the telegraph, electric current runs down a wire and activates an electromagnetic switch on the receiving side to produce a “click.” These clicks can then be timed to generate a pattern that can be mapped to letters—you know this as Morse Code.

But there’s a problem. If you have [...]  read more

A Flying Tesla? Sure! We Calculate the Power Demands

Elon Musk isn’t afraid to play around on Twitter. In a recent tweet, Musk suggested that a future Tesla would look like the flying car from Back to the Future.


p class=”paywall”>Ha ha. Funny. But could it really work? What would it take to make a flying Tesla that converts from driving to flying mode with the thrust coming out of the wheels? Time for some physics.

I can think of a couple options for getting a flying Telsa off the ground. The first method would be rocket propulsion. This seems to be what Elon wants to use (a natural choice because of the connection with SpaceX). In fact, it appears he’s not even joking.

I’m not a rocket expert, but it seems like you would have to keep refueling the rockets. It would be a nice stunt, but not for everyday use.

However, there is another way to make a car fly—some type of air thruster. It doesn’t matter if you use some type of jet engine or a rotor, the physics is mostly the same. In [...]  read more

A Magic Wand? Nope, Just Good Ol’ Fashioned Physics

Check this out. It looks like a magic wand that makes things float, but it’s just plain physics. I guess that’s what makes these kinds of toys so cool. They do things that go against our everyday experiences. Normally stuff doesn’t just hang in the air like this.

But how does it work? The answer is a fundamental interaction in nature—the Coulomb force (also called the electrostatic force). The Coulomb force is an interaction between any two electric charges. It’s sort of a circular definition, since you still have to define an electric charge. I will just say that the two most common electric charges are everywhere—they are the electron (negative charge) and the proton (positive charge). Along with the neutron, these three particles make up pretty much everything you see in everyday life.

For the Coulomb force, if the two charges are opposite in sign (negative vs. positive), there is an attractive force between them. If the two charges have the [...]  read more

How to Calculate the Physics in Super Smash Bros. Ultimate

Videogames can do whatever they like with their physics. They don’t have to follow our so-called laws of nature. Yet there are indeed rules in every game, otherwise the motions of characters wouldn’t make any sense. But what are the rules? What physics govern the motion of in-game stuff?

That’s where the real game begins: finding out the in-game physics. It’s just like doing real physics except it’s cheaper, because you only need the game and not something like a giant particle accelerator.

For this experiment, I am going to be looking at Super Smash Bros. Ultimate on the Nintendo Switch. The goal of the game is to fight other fictional characters. But you can choose just about any of the Nintendo characters from previous games. That means you can have a battle between Pac Man and Mario.

I’ve done this videogame stuff before—for example, the physics of Angry Birds[...]  read more

How Does a ‘Martian’-Style Gravity Assist Actually Work?

What the heck is a gravity assist and how does it work? The first question is easy—a gravity assist (also called a gravity slingshot) is a space maneuver in which a spacecraft gets a speed boost by moving past a planet. You could also use the gravity assist to slow down or even to change directions. However, in this case let’s just consider boosting the speed.

Yes, this gravity assist was used by a bunch of spacecraft like both Voyager 1 and Voyager 2 to get out the outer part of the solar system (and beyond). The maneuver was also used by fictional spacecraft like the Hermes in the movie (and book) The Martian. OK, actually my interest in gravity assists started with this tweet.


p class=”paywall”>So, let’s do it. Here is my introduction to gravity assists.

One of the things we like to do in physics is to make things as simple as possible while still keeping the main concept that we want to explore. This is where the famous “spherical [...]  read more

Trigonometry Is Essential to Physics. Here Are the Basics

You might have already passed that silly course with a title something like “Introductory Algebra and Trigonometry.” It covered a bunch of stuff, but the important part was that the class was a prerequisite for your physics course.

But do you really understand the very basic concepts of trig? Yes, I just call it “trig” because I always misspell trigonometry. Maybe you can use the double angle formula and you don’t have a problem with trig identities. It’s very easy to do some of the more complicated parts of trig while forgetting about the essence of trig (a nice name for a perfume, don’t you think?).

Honestly, I find that quite a few students make silly trig mistakes. It happens way more often than it should. Don’t worry, I’m here to help. Let’s start from scratch and go over the super basic ideas of trig. Yes, I will also show you why you need this.

Start With a Right Triangle

There are only two requirements for a right triangle. First, [...]  read more