projectile motion
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…
rallain | June 3, 2009I haven't seen the Pixar Movie "Up" yet, so don't spoil it for me. I have, however, seen the trailer. In my usual fashion, I have to find something to complain about. There is this scene where the old man releases balloons out of the house.
What is wrong with this scene? Also, would that be enough balloons to make the house float? Here is a shot of the balloons coming out of the house.
Ok, I was already wrong. The first time I saw this trailer I thought the balloons were stored in his house. After re-watching in slow motion, it seems the balloons were maybe in the back yard held down…
rallain | May 29, 2009Here is another one from a great podcast - Buzz Out Loud. I totally can't remember which episode it was, I listened to a several in a row mowing the lawn and doing outside type work. Anyway, the discuss was along the lines of:
Could an iphone tell if your parachute didn't open with its accelerometer?
The first and simplest answer would be "no". When you are skydiving, you quickly reach terminal velocity such that you are no longer accelerating. Maybe the built in GPS could use elevation data, but it seems like that is rarely used (and not very accurate). There is perhaps a way that work…
rallain | March 25, 2009Dan Meyer made this awesome photo. He posted it so that others could look at it and come up with lesson ideas to use with this. There are some very good suggestions in his comments. I wasn't going to analyze this because I didn't want to rob some students of the opportunity, but I can't resist. Also, I doubt the first step a student would use would be to google for the answer. HA! I just caught you, you googling student.
Ok - I will try not to post any data. However, I will post some info on how I analyzed this.
The photo is a composite image from a video clip of a person throwing a…
rallain | February 24, 2009Basically, the title says it all. Here is a short tutorial on projectile motion calculations with a spreadsheet.
Record your screencast online
I left out a lot of details, so maybe these links will help:
Spreadsheet tutorial for numerical calculations (video)
More details on numerical calculations
Projectile motion
rallain | February 2, 2009I enjoyed the super bowl commercials for the most part. You have to be careful not to have too high of expectations, or you will set yourself up for a big letdown. Here is a quick analysis of one of the commercials. This is a Bud Light commercial where at the end they throw a guy out of an office window because he suggests they save money by not buying beer. Are there any actual office meetings that serve beer? (Sorry if I spoiled the ending for you)
I am going to analyze the motion of the guy going out the window. Just because.
At some point in the future, I am going to make a short…
rallain | January 29, 2009I really didn't want to post this, but I am going to anyway. I used ScreenToaster.com to make a screen capture movie (with audio) of a tutorial on spreadsheets.
This should accompany my previous post on numerical calculations.
Free online screen recorder
rallain | January 27, 2009We have all seen the Kobe Bryant video of him jumping over an Aston Martin - this keeps coming up on the Internet. There has been vast discussions of whether this is real or fake. I will do my best to examine the evidence. In short (in case you don't want to read the whole thing) Kobe can most likely really jump that high, it is possible that there was some perspective trickery involved. Here is the video in case you are brand new to the WWW:
Oh - don't forget I already analyzed Kobe Bryant jumping over a pool of snakes. I voted that was real.
First, let me give a personal note to Kobe and…
rallain | January 7, 2009I saw this video posted on Physics and Physicists:
It reminded me that I had at one point tried to analyze this. I had actually posted something about this on the first generation of my blog (which no longer exists). I have found the analysis, and here it is from the archives. Thanks ZZ for reminding me.
Could this be true, or is it fake? I started to do an analysis of the trajectory, but I found the following frames:
Look at the guy's back. His back starts moving before the water bottle rockets. It must be some type of cable pulling him. If the rockets were propelling him, the rockets…
rallain | December 29, 2008In part I of this post, I talked about the basics of projectile motion with no air resistance. Also in that post, I showed that (without air resistance) the angle to throw a ball for maximum range is 45 degrees. When throwing a football, there is some air resistance this means that 45 degree is not necessarily the angle for the greatest range. Well, can't I just do the same thing as before? It turns out that it is a significantly different problem when air resistance is added. Without air resistance, the acceleration was constant. Not so now, my friend.
The problem is that air…
rallain | December 26, 2008College football season is coming to an end (I guess technically, the season is over - it is bowl season). Anyway, this is something I wanted to do a long time ago, but I kept getting side tracked. If I don't do it now, I will never do it. Most people know that a ball without air resistance (traditional projectile motion) goes the farthest if you throw it at a 45 degree angle. What if there is air resistance? Why is 45 the best angle without air resistance? What other questions are there?
I posted about projectile motion before - so you might want to start there. When people say "…
rallain | November 24, 2008This is an old video, but still interesting. In this video clip, Kobe Bryant jumps over a pool of snakes.
You are probably thinking what I thought when I see that - this doesn't look real. Really, it must be fake. Why would Kobe jump over a pool of snakes? Isn't that dangerous (even if there were no snakes in there he could hurt himself). Video analysis is needed. Is this fake or is it real?
Start with my favorite video analysis tool (tracker). Use this to get position time data.
Step 1: Get the movie. I used Mpeg Streamclip to get the movie in quicktime format from the flash video…
rallain | November 20, 2008Georgia Tech is playing Miami (not the real Miami, the other one Miami Florida). Right after a commercial, the camera shows this sign from a student (or just person) at the game:
(Sorry if the image isn't that great.) I had to pause the game and take a closer look at this sign. I am not sure I get it. In case you can't see, the sign shows two players and the trajectory of a ball (clearly labeled x and y axes). The equations are:
, [Momentum Principle](http://scienceblogs.com/dotphysics/2008/10/basics-forces-and-the-moment…)
What are "numerical calculations"? Why are they in the "basics"? I will give you really brief answer and then a more detailed answer. Numerical calculations (also called many other things - like computational physics) takes a problem and breaks into a WHOLE bunch of smaller easier problems. This is great for computers ([or a whole bunch of 8th graders](http://scienceblogs.com/dotphysics/2008/09/…
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 | September 6, 2008Here is the video in question:
Looks too incredible to be real for me. That is when I start to question things. Is this fake or not? To answer this, I took a clip that showed a person launching a grocery item over the isle. This was a good shot to look at because it was *mostly* perpendicular to the camera view. I then used [Tracker video analysis (free) tool](http://www.cabrillo.edu/~dbrown/tracker/) to get x-y-time data for the flying projectile grocery. The scale was difficult, so I just guessed that the guy on the left was 5 foot 10 inches. Here is the vertical position data for…
rallain | September 5, 2008**pre-reqs:** [kinematics](http://scienceblogs.com/dotphysics/2008/09/basics-kinematics.php)
My previous "basics" post was on kinematics (in one dimension). But what about two dimensions? In particular, what about projectile motion. My motivation here is that I was about to talk about analysis of a video that involved projectile motion and I don't want to go over all the stuff again and again.
Let me start with a generic, one-dimensional kinematic equation:
This relates the position (s), the velocity…
rallain | September 4, 2008One of my daughters was just reading Chicken Little to me. I don't know if you are familiar with Chicken Little, but she is a chicken that runs around telling people "The sky is falling". In my normal fashion, I started thinking about the plausibility of this. What would fall? What would you look for? Then I figured it out. The sky IS falling. It is ALWAYS falling and it has always been falling.
What is the sky? I am assuming the sky is the air. I will treat the air as a gas of single particles (which it isn't, but that's ok). So, why does this sky (air) do what it does? If you…