gravity
esiegel | February 24, 2010When you get into a tight place and everything goes against you, till it seems as though you could not hang on a minute longer, never give up then, for that is just the place and time that the tide will turn. -Harriet Beecher Stowe
Last week, our longtime reader Pamela asked if I could explain how the tides work. As you all know, when the tide comes in at the ocean, the water level appears to rise (and can do so significantly), while at low tide, the water level appears to drop.
This goes in a cycle twice per day, with the ocean level reaching its highest point twice daily (high tide),…
rallain | February 23, 2010I had so much fun creating graphs for the Red Bull Stratos Space Jump calculation, that I figured I should make some more.
Can you fall faster than terminal velocity? That is the question.
Air Resistance
Air resistance is a force exerted on an object as it moves through some stuff - air in this case. The magnitude is usually modeled as:
Rho is the density of the stuff the object is moving through
A is the cross sectional area of the object
C is the drag coefficient of the object - this depends on the shape (a cone would be different than a flat disk)
v is the magnitude of the velocity of…
esiegel | February 22, 2010Free energy will promulgate a forward leap in human progress akin to the discovery of fire. It will bring the dawn of an entirely new civilization -- one based on freedom and abundance. -Sterling Allan
Of course, when Sterling Allan talks about free energy, he's talking about natural energy from sources like wind and solar, not the violating-the-laws-of-thermodynamics type of energy.
There is, of course, no such thing as truly free energy, or energy that we can take out of nothing and use for something, which is why perpetual motion machines not only don't work, but are physically impossible…
rallain | February 19, 2010Red Bull is sponsoring this sky dive from really really really high up - Stratos: Mission to the Edge of Space. Seems dangerous. The basic idea is that Felix Baumgartner will take a balloon ride up to 120,000 feet and jump out. Here are some questions:
Will he reach supersonic speeds?
The Red Bull site says: "can Felix react to a 35 second acceleration to mach 1?"
How about the claim that he will free fall for 5 minutes and 35 seconds? That seems pretty short.
In 1960, Joe Kittinger jumped from 102,800 feet. Will 20,000 feet make a large difference?
Assumptions
Clearly, this can be a…
esiegel | February 12, 2010However time may be measured at the Naval Observatory, the clock seems to tick slowly here when Congress is out of town. -Richard Corrigan
The following is the mostly true (but somewhat fictionalized) story of the first clocks in the Americas. In the 17th Century, the finest clockmakers in the world were Dutch, going back to the time of Christiaan Huygens.
Image: A Dutch Longcase clock, courtesy of The Museum of the Dutch Clock.
Huygens determined that if you allowed a pendulum to swing just a little bit, the period of its swing could be used to keep time to incredible accuracy. By the mid-…
esiegel | February 8, 2010Ever since I was a child I have had this instinctive urge for expansion and growth. To me, the function and duty of a quality human being is the sincere and honest development of one's potential. -Bruce Lee
It isn't only our heros that expand and grow; the Universe does that, too! In the first three parts of our series, we talked about inflation, its end, and the hot big bang. But during all of this time, the Universe has been expanding.
This is probably the most confusing aspect of cosmology, so tread slowly through this. First off, it is space itself that is expanding. It doesn't make…
rallain | January 22, 2010Since my previous post on R2-D2 flying was so popular, I thought I would follow it up. I was going to add these two points in the comments, but a separate post seems to make more sense.
Point 1 - R2 flies at a constant speed
Well, he obviously doesn't always have to fly at a constant speed. However, in the clip I was looking at there are two important things in the analysis. What angle is R2's thrusters at? Is R2 flying at a constant speed? I found a much better quality version of the flying R2 from Billy Brook's site. That helped out a lot. So, on to Tracker Video Analysis (I always…
rallain | January 21, 2010You know I can't help but like Star Wars. Even with the new stuff, I watch it. Recently, I was watching the Clone Wars cartoon and noticed something odd about the way R2-D2 flies. I know what you are saying...."the odd thing is that he flies at all. Why didn't he fly in episodes 4-6?" Who knows. Here is the best image I could get of R2-D2 flying (from wookieepedia).
What is wrong? Well, maybe you can't tell from the image I posted. Here is a diagram of flying R2-D2.
If R2 (I can call him that because we are good friends) was flying like that, why would that be a problem? That would…
esiegel | January 20, 2010I'm always happy to receive questions from those of you interested enough to ask them, and every once in a while one of them feels just right to write up an article about it. Today's comes from Brad Walker, who asks about the inside of gas giants. Specifically,
The question pertains to the insides of gas giants like Jupiter... My question is, supposing Jupiter is made of Metallic Hydrogen, and it was dragged close enough to the sun that its atmosphere evaporated, what would be left? How would it go from a very strange non-terrestrial core to a rocky body like CoRoT-7b? Why wouldn't the…
esiegel | January 12, 2010There are two mistakes one can make along the road to truth... not going all the way, and not starting. -Siddhārtha Gautama, a.k.a. Buddha
Last week, I started a new series on The Greatest Story Ever Told, about the origin and evolution of the Universe. In it, I asserted that inflation is the very first thing we can definitively say anything sensible about, and that it happened before the big bang. This runs contrary to a lot of statements out there by a lot of reputable people, including this "timeline" image from Discover Magazine:
Everything else aside, it's very important to remember…
esiegel | January 8, 2010The more I examine the universe and the details of its architecture, the more evidence I find that the universe in some sense must have known we were coming.-Freeman Dyson
When we look out at our Universe today, we see all sorts of beautiful things throughout space, from galaxies and clusters, distributed roughly evenly throughout space:
to the cosmic microwave background (also known as the last scattering surface), radiating at the same temperature in all directions.
We also see, when we try to measure the shape of the Universe, that there are three major possibilities: it could be flat…
rallain | January 4, 2010This is great. Many people have already reported google's apple-dropping homepage in honor Newton's birthday. In case it disappears, here is a screen shot.
So, I got this awesome note from Dale Basler. He said that his class had analyzed this falling apple animation. What a very Dot Physics-y idea (check out his analysis). He said they were questioning the results which might be due screen capture issues. I decided to reproduce this.
I captured the motion with Apple's Quicktime X screen recording feature. I then used Tracker Video Analysis - which now has an autotracking feature that…
rallain | January 3, 2010Wow. In xkcd 681 comic, there is an impressive illustration of the common term "gravity well". Here is a small part of that large image:
I can't resist. I must talk about this awesome illustration. My goal for this post is to help someone understand that comic (although the comic itself does a pretty good job).
Energy
Energy is the key here. Here, I will talk about two types of energy - kinetic energy and field energy. In this case, kinetic energy is basically just the energy associated with something moving. Field energy is the energy stored in the gravitational field. You could…
esiegel | December 28, 2009Watch me as I gravitate (hahahahaha). -Gorillaz
Gravity -- unbelievably -- is the weakest force of all. But if you get enough mass together, gravity will overwhelm even the strongest outside influence. A simple case-in-point? You take a rock that's massive enough, and gravity will crush it into a spherical shape,
like it was nothing more than a drop of water.
And here we live on the surface of one of the smaller gravity balls in our Solar System. XKCD has a wonderful illustration of this today (and click for full-size).
The more massive and more compact your planet is, the harder it is to…
rallain | December 15, 2009Maybe you have noticed how much material there was (for me at least) in last week's MythBusters. One of the myths they looked at was the bus jumping over a gap in the road from the movie Speed. I am not looking at that myth, it has been discussed many times in many places. Rather, I am going to talk about scaling the motion. As typical with the MythBusters, they like to make a scaled down version of the event. It's cheaper that way. In this case, they made a 1/12th scale model of the bus and the road. The question was: how fast should the model go?
The first question to ask is: what do…
esiegel | November 30, 2009Follow humbly wherever and to whatever abyss Nature leads, or you shall learn nothing. -T.H. Huxley
We've spent a little bit of time talking about dark energy, including what we think of it, how we first discovered it, and how we knew that there wasn't just something out there blocking the light. It seems to be the latest abyss that Nature is leading us, so we needed to look beyond the type Ia supernova data and see what else the Universe was telling us.
Image credit: Don Dixon.
So what do we do? First off, we can try to measure how much matter is in the Universe independent of anything…
esiegel | November 23, 2009The cradle rocks above an abyss, and common sense tells us that our existence is but a brief crack of light between two eternities of darkness. -Vladimir Nabokov
Last Friday, I posed a question to you, and you kindly responded by voting as to whether, when you crossed the event horizon of a black hole, the lights would stay on or go off. The results so far?
What do I have to say? Good for you! Just because no light gets out doesn't mean that you can't see the light that comes in! When you're in your spaceship, very few things matter.
You could be in a strong gravitational field, like exists…
esiegel | November 13, 2009Can you touch your toes? Seems like an easy thing to do for those of us who have the flexibility.
Now, here's the challenge. Stand with your back and your heels pressed up against a wall, and now try to touch your toes.
You can't do it! Not without putting your hands down on the floor, you can't. There's a super-simple reason for this: center-of-mass.
For human beings, your center-of-mass is somewhere in your abdomen. It's lower down for women than men, but in the abdomen region for everyone. When you typically bend down to touch your toes, you'll notice that the upper part of your body…
rallain | November 10, 2009This is for commenter JimP. How do you take into account uncertainty when using video analysis? A great question. The first thing to think about is where does the uncertainty come from? My first guess would that it would be from the user. Where does the user click? Is it right on the object in each frame? Is the scale set correctly? I guess there could be other sources of error - maybe there are repeating frames that are a result of encoding. Maybe there is interlaced video frames.
Well, what to do? I will just look at one motion in particular and do the analysis several times. I…
rallain | October 12, 2009I put together this short presentation on fake videos for a class. What the heck, I will also put it online so that maybe some other people can use it. So, here it is. I have it in many forms. First, a video of me going through the talk. Then I have the keynote and PowerPoint files with the movies. Feel free to use it as you see fit. You might want to modify some of the files, I have no problem with that.
How to spot a fake video from Rhett Allain on Vimeo.
And the other versions:
Keynote (fakevideos.key - 46.1 MB) - this has the movies embedded
PowerPoint (fakevideos.ppt - 2.6 MB) -…