It might be surprising to see large planets have a pull comparable to smaller ones at the surface, for example Uranus pulls the ball down slower than at Earth! Why? Because the low average density of Uranus puts the surface far away from the majority of the mass. Similarly, Mars is nearly twice the mass of Mercury, but you can see the surface gravity is actually the same… this indicates that Mercury is much denser than Mars.
Okay, sure, but what’s heavier on Mars: a ton of feathers or a ton of bricks? [via kottke]
Physics and me never got along in high school and college, but I did always enjoy the low-budget demonstrations. It's one thing to see calculations on paper. It's another when the professor sets up a stuffed monkey on one side of the room and then shoots a sock out of a pressurized cannon angled at the trajectory you just calculated to make sure the sock hits the monkey on its way down from ceiling height.
In retrospect, shooting a monkey falling out of a tree seems kind of wrong.
And while we're at it, I always liked this demo too. A bicycle wheel gyroscope hangs from a rope, and when it spins its axis stays horizontal like magic.
This weekend I took my parents to visit the Greenwich Meridian – or did I?
The marked meridian on the site of Greenwich Observatory, where tourists line up to pose for silly pictures with one foot in the East and one foot in the West, has claimed to be zero degrees longtidude since 1884, but if you check your smart phone GPS on that spot, you’re NOT at exactly 0.000 degrees.
According to GPS, the zero meridian appears to be in a park adjacent to the observatory, and not in the section behind the fence that charges admission so you can “visit the meridian”.
What’s going on here?
Earlier this month, an article by Stephen Malys and others in the Journal of Geodesy revealed the reason behind the discrepancy. The technology used in the 19th century to determine the location of the zero meridian was subject to local distortions from the Earth’s gravity and shape of the local terrain. GPS technology uses measurements from satellites, which aren’t affected in the same way as technology located on Earth.
The dotted line is the much photographed meridian established in 1884. The solid line is where the GPS says it should be.
So the meridian really is in the wrong place. What does that mean for maps or for time? Well, the Ordnance Maps used in the UK were already using a slightly different zero meridian as reference point, because they were established before the 1884 meridian convention. And the effect of the new meridian location on Greenwich Mean Time, which determines Universal Time, is unnoticably small, so nothing much has changed.
Except, for a shorter line and a cheaper visit, you could technically skip the museum and the crowd of tourists and find the true GPS meridian about a hundred meters to the East of the Observatory in Greenwich Park. It’s probably not as fun a place for a family visit, though.
Last week I posted this photo of an animation that was used regularly during the NCAA Men’s Basketball Tournament and asked you to divine which of the multiple problems* bothered me so much. I think I’ve left you on pins and needles long enough.
I am a fan of gravity, which seems to be conspicuously absent from this animation. What is with the slack in the cables (for best results, imagine I’m doing a Jerry Seinfeld impression)?
To avoid the viewing problems with the photograph, I have created a whole new set of viewing problems by cartooning** the situation for you.
As the pictured screen slides into place it stops and wiggles side to side (green, above) perpendicular to the force of gravity. Virutally all components show some degree of movement around their potential pivot points (orange), indicating that few of these points are fixed and, therefore, are not fully supporting the screen. We also know the screen has some mass because of the momentum induced wiggle.
Gravity pulls down (green, below). Those cables should not be slack (red), but mostly taut (cyan). The connections below should not be perfectly straight (red), but be slightly flexed (cyan).
If the wheels on the cable are attached, but not rigidly fixed (allowing the aforementioned wiggle), to the gantry above, they should be angled toward the screen. If they are not fixed at all, they should align themselves above the corners of the screen with some variation due to friction and momentum (and due to trigonometry).
Even if we assume that the screen’s weight is fully supported from below, the screen should be angled either toward or away from the viewer. The direction of tilt would depend on small variations in the screen’s position as it settled. It could, theoretically, align perfectly straight up and down (not leaning), but I’ll let Dr. Ian Malcolm explain to you why this is vanishingly unlikely to occur.
I can identify two options that probably don’t violate the laws of physics. One, the NCAA Basketball Tournament has gone full Space Jamand is being played in the zero gravity of space. Alternatively, the force of gravity could be pointing toward the top of the screen (green, below). Neither of these options explain how the dudes in the background are staying in their seats.
**I’m using the scientific definition of cartooning here, which means to create an explanatory drawing to make your point less clear and more obtuse to those who might otherwise criticize your thinking (they get derailed by worrying if they are dumber than your or if you are just being unclear – this is called social engineering and is totally ethical and everything).
We all know how gravity is supposed to work. Without air resistance, a feather and a bowling ball (the standardized materials for all gravitational tests) should accelerate toward the center of the Earth at the same rate, thus striking the ground at the same time. Humans have tested this. It works.
Although we know this thing, it is so far removed from our daily experience that it is still stunning to watch it happen. This fundamental principle is nicely illustrated in this video from the BBC. The video also nicely shows how amazed a roomful of individuals who know how the experiment will work can be when the experiment works exactly as expected.
That is why we need the scientific method to rigorously test hypotheses and incrementally build our knowledge of how the universe works. Our day-to-day experience of and intuition about the world is extremely valuable, but also extremely deceptive.
For the record, the tortoise vs hare in a vacuum race I alluded to in the title would be incredibly inhumane and disappointing, in addition to having no winner – unless, UNLESS we had the tortoise and hare race in spacesuits. Why aren’t we racing animals in spacesuits?
