1. 2012
    Nov
    03

    Local measurements: the Rosslyn escalator

    Posted by David Zaslavsky on

    On my way to (and from) China last month I passed through Rosslyn Metro station, which has the distinction of hosting the third longest escalator in the world.

    How long is it?

    So long, you could… okay, I won’t bore you. But seriously though: suppose I wanted to actually measure how long the escalator is? The obvious method is to pull out a measuring tape and run it along the length of the escalator, but that’s hard without a helper.

    What I need is a measurement method which is local: roughly speaking, something I can do using only objects within reach. Fortunately, physics provides such a method. I can (and did) time how long it takes to ride the escalator from one end to the other, then wait at the bottom for that much time and see how many steps passed by. Then the length of the escalator is just

    $$\text{length} = \text{length per step}\times\frac{\text{steps}}{\text{second}}\times\text{time of ride}$$

    On my way down, I timed the ride at 140 seconds. I didn’t feel like waiting a full 2+ minutes to count steps (people would have thought it kind of …

  2. 2009
    Oct
    08

    LHC to test hyperdrive

    Posted by David Zaslavsky on

    Wait, what?

    Just stumbled across this nifty little idea: that a particle moving at high speed can actually repel a stationary object in the other direction. I haven’t read the paper but if the summary is to be believed, this is very cool. Although it’s not actually faster-than-light propulsion, so not quite the hyperdrive of science fiction.

  3. 2009
    Aug
    28

    Failure of the equivalence principle?

    Posted by David Zaslavsky on

    Here’s an interesting physics tidbit, to close out a long break from the science on this site: a couple of scientists claim to have proposed an experiment which theoretically should be able to distinguish between gravitational and inertial accelerations. This would break one of the most widely accepted laws of physics, the equivalence principle of gravitational and inertial masses — in other words, the belief that the \(m\) in \(F=ma\) is the same as the one in \(F=-GMm/r^2\) is now being challenged.

    But I’m not really buying it. The equivalence principle is one of those things that just makes sense, that’s why it’s been accepted so widely for so long. If it’s going to be overthrown, I need to see hard evidence, and nobody’s even done this experiment yet. I’m not familiar with the calculations they did that predict different responses for gravity and kinetic acceleration, but it’s easy to imagine that they might have missed a term somewhere, or perhaps one of the equations they used is incomplete, or whatever, and that would make physics a lot more consistent (albeit a lot less exciting) than the alternative of …