During the Age of Sail, ships circled the globe on voyages of discovery and trade. That era ended in the 1800s, when coal-fired steam engines began to replace wind power. Now we may be entering a new age of sail—but this time in space. Reversing history, engines and fuel could be replaced by sails on … Read more
We can break that diagonal motion down into horizontal and vertical portions; for now let’s just focus on the former. Say you start with a horizontal velocity (v1) of –1 meter per second and rebound with a horizontal velocity (v2) of +1 m/s. The change of sign indicates the reversal of direction. Think of it … Read more
Have you ever sat on the bottom of a swimming pool and pondered your watery ceiling? Most of the surface is a sheet of light blue, and you can’t see through it, even though the water is clear. But right above you, there’s a round window of transparency. And here’s the awesome thing: Through this … Read more
However, since this force is applied at the feet, far from the center of mass (r > 0), it’s going to produce a torque. In this case, the torque would cause a forward angular acceleration, tending to deposit the jumper face down in the sand. So athletes use a few different techniques to counter this … Read more
A gymnast can actually perform both of these types of rotation at the same time—that’s what makes the sport so interesting to watch. In physics, we would call this type of movement a “rigid body rotation.” But, clearly, humans aren’t rigid, so the mathematics to describe rotations like this can be quite complicated. For the … Read more
The angle at which the light hits the panel, θ, is measured from a line perpendicular to the surface. This means you will get a maximum solar panel power when the light is shining straight-on (θ = 0), since cosine(0) = 1. OK, let’s do a quick calculation. The intensity of sunlight at the location … Read more
When the elevator is stopped, the two forces are equal and opposite, and the net force is zero. But if you’re accelerating upward, the net force must also be upward. This means the normal force exceeds the gravitational force (shown by the lengths of the two arrows above). So you feel heavier when the normal … Read more
Theres a famous star that I’m sure you’ve seen in the sky. Its name is Betelgeuse, and you can find it in the Orion constellation, where it marks Orion’s right shoulder. If you want to call it “Beetlejuice,” I’m fine with that so long as you don’t say it three times. But something is going … Read more
Melting an ice cube takes 3.34 x 105 joules per kilogram. So a single ice cube with a mass of 50 grams would take 16,700 joules. You can already see that melting stuff takes a bunch of energy. If you want to melt a metal door, you have to do two things—increase the temperature to … Read more
Just because you see something done in a movie, that doesn’t mean you should try it yourself. Take, for example, a human running on top of a moving train. For starters, you can’t be sure it’s real. In early Westerns, they used moving backdrops to make fake trains look like they were in motion. Now … Read more
