Category Archives: Physics

The reverse sprinkler, part 3: results

In part 1 and part 2, we introduced the reverse sprinkler problem and tried to gain some theoretical insight. In this final part, we will simulate five different sprinkler designs and interpret the torque results.

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The reverse sprinkler, part 2: theory

In part 1, we introduced the reverse sprinkler problem and attacked the most ideal case, ignoring factors such as pipe diameter. Now we will perform a more general analysis.

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The reverse sprinkler, part 1: introduction

A short version of this post series is also available as a YouTube video here. The reverse sprinkler is a physics problem that has long been a source of confusion and debate. It is sometimes known as the Feynman sprinkler problem … Continue reading

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Directly downwind faster than the wind

Is it possible to build a wind-powered vehicle that can continuously travel faster than the wind, in the same direction as the wind? Like the airplane-on-treadmill problem and the Feynman sprinkler problem, this question has spawned endless Internet arguments. Continue reading

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Electromagnetic radiation from accelerating charges

Electromagnetic radiation is something that has often eluded my intuition. Electrical engineering depends on numerous abstractions: current flowing in wires like a fluid, capacitance/inductance in lieu of near field interactions, antenna theory to model far field interactions, etc. These abstractions … Continue reading

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MEMS oscillator frequency increase from helium

You may have heard of the incident where a helium leak suddenly disabled many iPhones at a medical facility. The root cause — tiny MEMS oscillators being susceptible to helium leaking into their hermetically-sealed casings — is interesting but not … Continue reading

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H field and material boundaries

For a long time I thought of the H field as being generated by free currents only. The problem with this view is that it leads us to make erroneous assumptions. We know from the definition of H that:   … Continue reading

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Magnetic field of a ferrite core solenoid

Consider a solenoid made of wire wrapped around a rod made of iron, ferrite, or other ferromagnetic material: It is well known that the magnetic field will be significantly stronger inside such a solenoid, compared to an air core solenoid. … Continue reading

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Weather balloon physics

One of the simplest solutions for sending measurement instruments up into the stratosphere is a rubber balloon filled with hydrogen or helium. While the physics of such a balloon would seem to be simple, there are actually some interesting considerations.

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