## How Much Does a Fly Hitting a Train Slow It Down?

[caption id="attachment_27068" align="alignright" width="480"] The Scenario: a fly hitting a train.[/caption]Say you have a train, a locomotive traveling along a straight railroad track. The atmosphere is absolutely free of every conceivable impediment except for one lone housefly. Unfortunately (for the fly), it and the train collide head-on. You have a fly hitting a train. Clearly, the fly will turn into a smear. How much does that fly slow the train down that it has hit? The train will suffer no apparent change in speed, yet it does slow down, even if there is no obvious change. How much does it slow down? Fly Hitting a Train: Specific Numbers We will attempt to use realistic numbers. We choose the following: Locomotive: 4,000 tons [a light train] Fly: 14 milligrams Locomotive Speed:…

## In Simple Terms: The Heisenberg Uncertainty Principle

[caption id="attachment_26306" align="alignright" width="480"] L to R: Niels Bohr, Werner Heisenberg, Wolfgang Pauli[/caption]Werner Heisenberg (1901-1976) was yet another bright German physicist. He was a "founder" of quantum mechanics, the physics of the subatomic. As with astrophysics, behavior at this level appears to vary from the physics of the everyday world. A Brief Description The velocity of an auto of mass m can be measured accurately. If its velocity remains constant, its location over time is predictable. This is the norm according to ordinary human experience. Yet, at submicroscopic levels, physicists experienced something different. For certain measurements, various pairs of variables could not both be accurately known simultaneously. Simultaneous measurement is only precise to a point. These pairs of variables are termed conjugate variables. The Standard Example The simplest example is…