Category: Learn

A bolt of lightning.

Electrical Energy Density Derivation

In this post, we’ll do a mathy proof of the electrical energy density of an electric field. Here’s the statement: For any continuous distribution of charge where the electric field vanishes at infinity, the total electrical energy of the system is given by where is a small volume element, is […]

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Lava from volcano.

The Leidonfrost Effect is cool

You can test the Leidonfrost Effect at home right now. Check out this video. Ever dip your hands in molten lead? (Skip to around 4 min) Ever dip your hands in liquid nitrogen? The explanation All three phenomena are a result of the Leidonfrost effect. The explanation is pretty simple. […]

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Learn Projectile Motion (Again)

Projectile Motion is the most classic high school physics problem in existence. It might be a little bit boring, but it’s very important to master, and it’s a great way to apply what you’ve learned in kinematics. Here’s the set up. First of all, what are the forces acting on the ball […]

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A glass of hot chocolate.

The Hot Chocolate Effect

The hot chocolate effect The Hot Chocolate Effect is a cool little experiment you can try at home right now. Take a cup of hot water and tap a spoon against the bottom of the glass. Then add your favourite hot chocolate powder and stir it in. Now tap at the […]

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Wave equation diagram.

The Wave Equation for Ideal Strings

One of the most important equations in physics is the wave equation. In this post, we will derive the wave equation for the case of a transverse wave on a string. We’ll also find this speed as a function of tension and linear density. Let’s get started. Consider an infinitesimal rope […]

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A plasma sphere

Energy of a Charged Sphere

In this problem, you’ll be calculating the energy of a charged sphere. This can be pretty hard if you’ve never done anything like it before. But it’s super easy once you know the trick. Give it a shot! You have a solid metal ball with a total charge and a […]

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Picture of a whirlpool on a beach

Whirlpools in your Bottle

You’ve probably played around with whirlpools in your water bottle. In this problem, you’ll be analyzing an idealized form of this experiment. You have a cylinder filled with water. Put it on a spinning disc so that the cylinder is spinning around it’s primary axis at an angular speed . Gravity points downwards […]

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Photo of Albert Einstein

What is a 4 Vector?

Special relativity is super simple when it’s all time dilations and length contractions. But if you study relativity a little more deeply, you’ll notice a lot of talk about 4 vectors? What the heck is a 4 vector and why do you need them? A simple analogy I’m assuming you know what […]

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Two springs in series

How to Solve Springs in Series

Most physics students have studied springs before, but not many have studied springs in series. Did you know that having  identical springs end to end actually makes a new spring that’s half as strong? Cool right? How do you figure this out? Take a look at the diagram above and see […]

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If your car is travelling at the speed of light, how fast are your headlights moving?

This is a classic problem in relativity. Let’s rephrase it a little bit for clarity. Let’s say is moving past at the speed of light and is moving past at the speed of light. and are all moving in the same direction. How fast is moving relative to ? I’ll give […]

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