Tag Archive | physics

The Eternal Fall

Here is a video of some astronauts on the International Space Station (ISS).  It depicts some common (and uncommon) activities that they do aboard it.  It has background music – so turn down your volume if you are at work.

As you can see, astronauts in space operate in a ‘zero-gravity’ environment.  They float around effortlessly and don’t fall toward the ‘floor’ of the space station.  Water, in a space station such as the ISS, automatically assumes the shape of a ball and floats around.  This is indeed, quite a strange environment.  But have you ever stopped and wondered – why are the astronauts actually floating?  Is it because there is no gravity in outer space?  Is it because the earth’s pull is so weak that it no longer affects them?  Is it because they are constantly being pushed away from the earth by rockets?  Or is it something more subtle?  In this post, we shall explore the phenomenon of micro-gravity.

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Three Strokes and Out

In this post, I will discuss the working of a four stroke internal combustion engine such as the one used in most automobiles.  The engine of most modern cars runs on gasoline/petrol.  It does this by burning petrol in air and using the energy of the hot gaseous by-products to produce mechanical movement and motion of the car.  We shall explore how fuel and air are combined in the engine, how the controlled explosion is initiated and how all the heat is converted into rotational energy for the wheels.

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The Day The Earth Stood Still


What would it take to make the earth stop spinning?  This scenario is not unheard of in B-movies and bad sci-fi shows.  It isn’t uncommon to have plots involving the Earth’s core slowing down or aliens from a different galaxy stopping the Earth’s rotation.  A lot of these plots have the Earth stop spinning either instantaneously or within a very short period of time.  Intuitively, we know that spinning bodies have energy.  The Earth is a pretty massive spinning body.  How much energy would the Earth have to shed to stop rotating?  How would that energy affect us worldly inhabitants?

Here, I will discuss the physics behind rotation and rotational energy.  We shall use simple facts about the Earth’s rotation to calculate what would happen to it were it to stop spinning.

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Aircraft and Treadmills

In this post, I want to address an interesting thought experiment that I “found on the internet”™.  The problem is usually phrased in a few different ways but here is the version I have chosen to attack.

The Problem

It was a calm, sunny day at Horsehead Airport.  An aircraft, ready to fly to a foreign country lines up on the airport runway, carrying out final preparations for takeoff.  On this calmest of days, the evil Dr. Horrible has decided to discombobulate the pilot of our aircraft by swapping out the runway for a long conveyor belt.  This belt is powered by a very powerful motor that can drive the conveyor belt and anything on it at  enormous speeds.  As the pilot throttles up for takeoff, he powers up his conveyor belt to move backwards.  His aim is to move the conveyor belt backwards just fast enough to cancel the aircraft’s forward motion, hence preventing the aircraft from achieving takeoff velocity.  Does he succeed in doing so?  Can the pilot still takeoff his aircraft or is he at the mercy of the evil Dr. Horrible?

What do you think would happen?  Take an intuitive guess.  Part of being a good scientist is getting good at making defensible guesses.  Also part of being a good scientist is realizing when your common sense and gut feeling are going to fail and training to guess more systematically.  When I first ran into this problem many years ago, my gut feeling was “Hmm..  if the conveyor belt moves as fast as the aircraft but in the other direction, then the two would cancel each other out and the aircraft would be at rest, unable to take off!”.  My second thought was “Wait a minute.. maybe the engines can produce enough airflow over the wings that the plane can lift off even if stationary!”.  The Mythbusters investigated a similar question a while back (here is a sneak peek).

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