Physics Puzzle: Changing an Oscillator’s Spring

Here’s a nice physics puzzle I was asked a while ago.
Suppose you had a harmonic oscillator - a very simple one, with no friction or driving force. Suppose your oscillator’s oscillating with an amplitude A and that the spring constant is k. Now suppose you slowly change k from its initial value to some final […]

Physics Puzzle: Newton’s Cradle

We’ve all seen this executive toy somewhere:

As the ball comes down and a collision occurs, it comes to rest while another ball at the other end rises up. This repeats ad infinitum - at least in theory - and illustrates perfectly the principle of conservation of momentum - the momentum of the colliding ball on […]

Physics Puzzle: a Race Between Two Marbles

For our weekly puzzle, here is a physics brainteaser to test your mechanics skills (did I mention already those are my favorite puzzles?)

Consider a marble which rolls from start to finish along one of two paths: either an inclined, yet straight plane (B), or a series of valleys and hills passing below that plane (A). […]

Physics Puzzle: Rope Between Two Poles

A good puzzle, someone once told me, is one that can be solved by a bright high-schooler, and yet challenge even a seasoned practitioner. As a puzzle-aficionado, I second that notion, which is why mechanics puzzles are my favorites. It is the most intuitive discipline and the first to be studied in both high school […]

The Pendulum and Truck Puzzle

Still working on the next part of our neural networks tutorial, but in the meantime, a puzzle.
A stationary truck has a pendulum of length L and mass m attached to the top of its insides (see figure A below). The truck driver hits the acceleration and as a result everything sort of gets “thrown back” […]

Bus Stops and the Electron Charge

While I’m preparing the next part in our neural networks tutorial, let’s digress a bit and talk about something completely different.
You’re standing outside, waiting for the bus to arrive. Being a physicist, you busy yourself with building some model until it does. Assume the rate of bus arrivals is - for example, 5 buses […]

The Ice, Water and Oil Riddle

Well, this is not really a riddle but more of a fun experiment.
We all know ice floats on water. We also know oil floats on water. Now the question is, if we take a glass and fill it with 50% water and 50% oil, and afterwards drop in an ice cube, where will […]

The Psychotic Train Riders Puzzle

Here is a somewhat cruel physics puzzle which illustrates the idea of momentum conservation.
Consider a train full of passengers moving along on a frictionless rail at a constant speed, v. In order to increase its speed, the passengers decide to throw themselves off the back end of the train, making use of the principle of […]

Getting Shot Isn’t So Bad For You

In this post we’ll be doing some simple, yet illuminating calculations.
A typical baseball weights about 150 grams and can reach velocities of up to 100 mph, or 40 m/sec, and so its kinetic energy is about and its momentum about . On the other hand, the bullets of a .38 special handgun - […]

Beating your Guitar into Tune

If you have any musical friends, this should get their attention (if it doesn’t, just spill petrol over their musical instruments and ignite. THAT will).
Basic trigonometry tells us that the rule for adding two sines is as follows:

It turns out that if our ear is exposed to two sounds which have similar frequencies, it only […]

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