gravity
rallain | June 26, 2009Was the moonwalk fake? No, not the Apollo landings. I am talking about Michael Jackson's moonwalk. You got to admit, he had a big impact on a lot of stuff and this is my way to give him respect - physics.
I am sure you know about the moonwalk. Maybe you can even do the dance move yourself, but how does it work? First, here is a clip of MJ doing his stuff.
As a side note, I can't remember where I saw it but there was a great discussion of the history of the moonwalk. If I recall correctly, some were saying Michael didn't create this move. One thing is for sure, he made it popular. Now…
rallain | June 24, 2009I made this screen cast for my algebra-based lab. Maybe you will find it useful also. This is a tutorial using Tracker Video Analysis (an awesome free program as I have said many times). In this tutorial I analyze a moving cart that shoots a ball up and lands back in the moving cart (called a Howitzer cart). The video is available at the LivePhoto Physics site.
Screencasts and videos online
rallain | June 22, 2009Maybe this isn't the best video to analyze, but it sure is funny. I am not sure why it is so funny - maybe you should just watch it first.
Sledgehammer Funby Stressmaker
I don't really know why these guys are putting explosive on sledge hammers. Sure it looks fun, but I think I would pass. Anyway, here is the part I was curious about.
Did the exploding hammer lift him off the ground, or did he jump as a reaction to the explosion. It kind of looks like he was lifted, but I am not sure that is possible. Video analysis to the rescue. (using Tracker Video) So, I assumed the sledge hammer…
rallain | June 12, 2009Jennifer over at Cocktail Party Physics has a nice post about her trip to Disneyland. The one ride that would be fun to play with (in terms of physics) would be the tower of terror. Think of the cool things you could do with a video camera during that ride. It would be like a mini-vomit-comet. Anyway, I want to talk about one part of Jennifer's post.
"As one would expect, this lifted us out of our seats slightly, as much as the straps would allow, and we got that one glorious moment of seeming weightlessness, before reaching a jerky stop and being raised back up for another drop."
It is…
esiegel | June 11, 2009100 years ago, the way we viewed our Universe was vastly different than the way we view it now. The night sky, with stars, planets, comets, asteroids, nebulae, and the Milky Way, was viewed to make up the entire contents of the Universe.
The Universe was static, governed by two laws only: Newton's Gravity and Maxwell's Electromagnetism. There were the first hints that the Universe was made up of quantum particles, such as the photoelectric effect, Rutherford's first hints at the existence of the nucleus, and Planck's view that energy was quantized. But other than that -- and Einstein's new…
esiegel | June 9, 2009One of the toughest things to do in science is to figure out -- of all the things that exist in the world -- is which ones are relevant to your problem. Take the Leaning Tower of Pisa, for instance.
Specifically, I wrote about Galileo's famous problem, where you take two cannonballs, one that's 10 lbs and one that's 1 lb, and drop them simultaneously off of the Leaning Tower of Pisa, about 55 meters up.
Perhaps you'll make the simplest model, and say that the only thing that matters is gravity. Perhaps you'll neglect air resistance, friction, the Coriolis forces, wind, horizontal motions,…
rallain | May 14, 2009Last night was Wednesday, so of course I watched Mythbusters. You never know when a good blogging opportunity will come up. I could talk about the kinetic energy of arrows, but instead let me talk about their episode for next week. I only caught a glimpse of it in the preview. It looks like they are doing something about jumping on a see-saw and launching the other person. It could be this video they are looking at:
EMBED-Extreme Catapulting - Watch more free videos
From my analysis of this video, I found that the likely outcome was a broken board (if it were not fake). Also, if the…
esiegel | May 5, 2009There's a new scientific paper online today about a very special and rare type of star: an ultracompact X-ray binary star. (One of the authors is surnamed Maccarone.) Let's start by explaining what these things are, how they work, talk about this one in particular, and what it all means. You've heard of binary stars before; these are systems where, instead of having one fusion-burning star in it (like ours), there are two. It turns out that most star system in our galaxy are binaries. If Jupiter were about 70 times more massive, we'd be living in a binary star system ourselves.
Well, let's…
esiegel | May 1, 2009When you look up at the night sky, what's the first and most obvious thing you see? If you answered anything other than "the Moon" you're in serious need of some new eyes, because -- in terms of size, brightness, and detail -- the Moon dominates everything else.
But the one thing you'll always notice about the Moon? We always see the same face. Why is this? There's a simple explanation: all objects in the sky are like spinning tops. But some of them orbit larger bodies, which pull them into gravitational, elliptical orbits. The closer the small body is to the large one, the bigger the…
rallain | March 17, 2009Dear Ruff Ruffman,
My kids really like your show. However, there is a problem. You promote it like it is science, but the content keeps having mistakes in it. Previously, I pointed out your mistake about in infrared thermometer (if can't remember, you said the thermometer measures the temperature with a laser. In fact, the laser is just used to aim.)
So, you see, I don't just like to randomly attack people. The problem is that you are saying "hey look at science" but your science is wrong. I suggest you either a) stop pretending to be a science show or b) get a science advisor (I am…
rallain | February 13, 2009The local Society of Physics Students invited me to watch the movie Sunshine and then participate in a post movie discussion. There was one thing in the movie that really got me. Of course the movie made many of the common space mistakes. But this one didn't seem necessary. Let me outline this part of the movie (I guess I should say spoiler alert - although this isn't central to the main plot). Here are three frames of a comic I drew to reproduce the scene.
After watching Sunshine, the astronauts try to go from one ship to another without space suits (well, one of them had a suit).…
rallain | January 30, 2009Buzz Out Loud is one of my favorite tech podcasts. Unfortunately, I am a little behind in the episodes. However, in the episode 900 there was an email from a listener regarding LHC and black holes. The emailer claims that a massive black hole would mess up Earth's orbit. This is not quite true.
I was getting ready to make a lengthy post about how black holes work, but did a way more awesomer job than I could do. Stefan and Bee describe some very important points:
First, black holes created in the Large Hadron Collider are based on a theory that has not really been verified. So, it…
rallain | January 5, 2009I finally saw the movie WALL-E. Good flick, I liked it. There was, however, one part I must comment on. You know I can't help myself. I feel like the shark Bruce in Finding Nemo. I try not to attack, but there is a tiny drop of blood in the water. Here is the scene that I want to talk about:
I guess I should give a spoiler alert. Although, I will not talk about the plot of the movie.
In this scene, WALL-E is hitching a ride on this space craft. The space craft is entering a hanger deck of a space station. While the hanger door is still open, WALL-E is clearly hanging on so that he…
rallain | November 25, 2008You see this all the time in textbooks:
This is often described as "the acceleration due to gravity". Is this really the best thing to call this? No. A better name would be "the local gravitational field" and list it in units of:
Where does g come from? The usual source is from the weight, or gravitational force:
This is the best way to write it (in vector notation) but you will often see it written as:
which looses the vector nature. In the vector notion, the vector g is a vector pointing towards the center of the Earth.
Why not acceleration due to gravity?
Take the following case…
rallain | November 23, 2008One of my favorite podcasts to listen to while driving or mowing the lawn is [Buzz Out Loud](http://bol.cnet.com). Buzz Out Loud (BOL) is basically just a tech-based podcast, but very entertaining. Anyway, as part of my attention seeking disorder, I try to get mentioned on the show. I succeeded once when I posted my [Optimal Commuting Speed Calculator](http://www.dotphys.net/page1/page10/efficiency/calculator.html). When I heard Tom and Rafe talking about orbital speeds, I realized this was my chance. Find any tiny flaw in their reasoning and I could perhaps come up with a comment worthy…
rallain | September 23, 2008In my classes, I like to bring up the question:
*Why do astronauts float around in space?*
The most common response to this question is that they float around because there is no gravity in space. Some people take this a small step further and say that there is no gravity in space because there is no air in space. This is why they claim there is no gravity on the moon (even though there is - more on this later).
I like to start off with the concept of gravity. Gravity is an attractive force between any two objects with mass. Your pencil and your dog both have mass so there is a force pulling…
rallain | September 19, 2008Today I was talking about electric potential. My favorite analogy for electric potential energy is gravitational potential energy. But electric potential is something different. Electric potential (commonly called potential) can be defined as:
So, V is the electric potential in units of Joules per Coulomb or Volts.
What about gravitational potential? I am sure some astrophysicist use gravitational potential. Maybe they even have some units for it, but I have never seen it. My students asked me if there was such a thing as gravitational potential. I said, sure. Here it is:
I picked…
rallain | September 14, 2008Can you believe it? Have you seen this video?
Are you thinking what I am thinking? WOW. How could these people not follow my rules for cool internet video. Once again, here they are:
1Keep the camera stationary. This way I don't have to keep moving the origin in the movie.
2Don't Zoom. Same reason, this video followed that rule.
3Include a clear and obvious calibration object. A meter stick would work, or even a Kobe Bryant (I can look up his height). Maybe it could be a Ford F-150 that has a known length. Something!
4Include the mass and height of all people involved.
5Use high…
rallain | September 13, 2008Scale of the Line Rider
First, we assume that the line rider is on Earth and for low speeds will have a free-falling acceleration of 9.8 m/s2. Next, an arbitrary distance is selected. In this case the length of the sled is chosen to be 1 LU (Linerider Unit).
The goal will be to put the linerider in a free fall (where air resistance should be able to be ignored) and determine his (it could be a she, it is difficult to tell) acceleration in LU/s2. Then we can determine the conversion factor from LU/s2 to…
rallain | August 28, 2008I recently saw a comment on a blog somewhere about putting satellites into space (I think it was from a post about a rocket that blew up). The poster suggested using a giant catapult to put things in space instead of rockets. Maybe he or she was kidding, or maybe not. But I have heard this idea before. Would it work?
First, how do things get in orbit? Orbit is a motion in which the gravitational force on an object makes it move in a circle around another object. In order to be in a circular orbit, it takes a certain amount of energy.
Let me just start with some calculations. How fast…