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David Anthony Colarusso - Sadly not Havoc Dinosaur
Intermittent musings on the law, science, education, technology, design, and life. Also, I build things: furniture, software, reasoned arguments... To learn more about that, click a persona below for my eponymous website.

Tabletop Explainer

I started this video series while teaching high school physics and astronomy back in 2007. With over five million views, it is the biggest thing I have done on the Internet. Be warned, however, sometimes years pass between postings, but never fear, I am always “working” on the next video.

Conservation Laws (1) Electricity & Magnetism (3) Newtonian Dynamics (1) Positional Astronomy (2) Quantum Mechanics (1) Relativity (2) Updates (2)

How to Build a Paper Quadrant

by David Colarusso - April 3rd, 2007

The quadrant is a simple tool for measuring the altitude (angle) of an object above the horizon. This episode makes use of a printable template found at:


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What is quantum tunneling?

by David Colarusso - March 25th, 2007

Einstein may have believed God doesn’t play dice, but God need not conform to Einstein’s beliefs. This piece explores the phenomenon of quantum mechanical tunneling whose explanation requires us to accept the reality of quantum mechanics. It’s not a trick; it’s reality.


Update: People have been asking for the math. So here it is. The Sun’s core temp is ~13.6 MK. For hydrogen nuclei the Coulomb barrier is roughly 0.1 MeV. This corresponds to a temperature in excess of 1 GK! Luckily, tunneling and the distribution of speeds among nuclei lower the actual temperature required. So without tunneling even the Sun’s core isn’t hot enough for fusion. To see most of this worked through, check out this link:
for a less mathematical explanation, try:

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Could that actually happen? Phylm examines the bus jump from Speed

by David Colarusso - March 20th, 2007

In the movie Speed a bus is forced to jump an unfinished portion of highway to avoid setting off a bomb on the bus rigged to explode should it go below fifty miles an hour. Of course, they make it, but we want to know if this could really happen.


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What is the conservation of angular momentum?

by David Colarusso - March 11th, 2007

What do bicycle wheels, figure skaters, and exploding stars have in common? That’s right, angular momentum. This video quotes three others: Rotating Person and Bicycle Wheel, Skating: Scratch Spin, and Exploding Neutron Star.


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How to build a simple electric motor, plus how it works.

by David Colarusso - March 3rd, 2007

A fast-paced time-laps demo of how to build your own electric motor, this segment was a lot of fun to make. I hope you enjoy it. Plus, you can now subscribe to the Tabletop Explainer via iTunes.


Also, by popular demand, here’s a TROUBLESHOOTING GUIDE

First, it’s important to understand the context of the “Build Your Own Motor…” video. It’s a demonstration aimed at solidifying the ideas presented in two earlier videos. If you haven’t already, you should watch the whole set:

1) What is the magnetic field?

2) Electricity & Magnetism Hand Rules (part one)

3) How to build a simple electric motor, plus how it works. (above)

The main idea here is that charges moving through a magnetic field experience a “push” perpendicular to the direction of their motion. This force is also dependent upon the direction of the magnetic field. The fact that the wire is stripped on only one side alternates the current from “on” to “off” every half rotation. So halfway through the spin, the ring coasts through until it gets current again receiving a “kick.” It’s a poor man’s commutator. The particulars of this kick/force are discussed in the second video. Armed with the knowledge from the above videos, you should be able to troubleshoot most of the problems that arise. The key is to make sure you understand the concepts first.

That being said, here are the most common issues I’ve seen my students have when working on their motors:

1) They strip the wrong part of the coil.

1.a) Most often they forget that they are supposed to strip only the underside of the wire on the arms of the coil. They mistakenly strip the whole wire. This could cause the coil not to spin properly and also in some cases to over heat.

1.b) They strip the bottom of the wire when the coil is lying down. Make sure you are stripping the underside of the coil when it is oriented as an upstanding “O.” Ask yourself, will the charges flowing through this wire get a push in the right direction according to the rules set out in the second video?

2) The coil isn’t symmetrical. Before you connect up the power, the coil should spin quite well with just a little push. If the arms are off center this can be a problem.

3) The coil isn’t wound tightly enough. The coil should be very tight and neat.

Also you could be using the wrong type of wire. It needs to be thin, but also insulated. I’ve had good luck with this wire.

If something isn’t working ask yourself “why?” You should have enough information to figure out the answer. After all, that’s half the fun. I hope that helps.

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