analysis
rallain | October 20, 2009I don't really know what that title actually means. So, I have been having problems with my PASCO projectile launcher devices. I will just call them launchers (they are really cannons). In my previous post, I looked at the launch speed from a launcher shot horizontally and vertically. The problem was that I was getting different launch speeds for the vertical and horizontal shot. So, here is my plan: shoot the ball and a variety of angles from 0 to 90 degrees and see how the launch speed changes. I will only use the data from video analysis (of course using Tracker Video Analysis)…
rallain | October 13, 2009The last time I looked at this projectile motion lab, I was confused. My different methods for measuring the launch speed of the ball were not even close to being consistent. So, I am bringing out the big guns - video. I made a video of the ball shot both horizontally off the table and vertically. No point posting the whole video (unless you really need it), but here is a screen shot of what the setup looked like.
These videos were made with my flip video camera, it doesn't have adjustable shutter speed so that there is some blur. Also, notice the carbon paper on the floor. This is so…
rallain | October 11, 2009The other myth the MythBusters looked at last week was the phrase "knock your socks off" (along with the dropping and shooting a bullet myth). But before that, let me complain.
Maybe it is just me, but I totally cringe when these guys use the word 'force'. Force probably isn't the best term to use to describe a collision especially when you are talking about one of the objects. "oh, we will just give this object some more force to impact with that other object". Force is not a property of an object, but rather an interaction between two objects. When two things collide, you really need…
rallain | October 9, 2009If you didn't catch the latest MythBusters (yeah! new episodes), they did something straight from the physics textbooks. Just about every text has this example of shooting a bullet horizontally and dropping a bullet from the same height. The idea is that they should hit the ground at the same time. No one but the MythBusters could actually show this demo with a real gun.
The Physics
I am going to do some calculations, but I want to first write about the physics that accompanies this idea (and you can actually do it your self without the gun). What physics principle does this demo show?…
rallain | September 30, 2009This is really a lab that I have students do, but I am pretty sure they don't read this blog - so it is ok. If they are reading this, hi!
We have these projectile cannons that shoot small balls. In order to look at projectile motion, they need to first determine the launch speed of the ball. I have a great method for this. Basically, shoot the ball horizontally off the table and measure how far horizontally it goes. You can get the final location of the ball by having it hit a piece of carbon paper on top of normal paper. If you don't know what carbon paper is, you are young.
Anyway,…
bcohen | September 25, 2009Instead of me answering that, I wondered instead how other people have argued about the question. To be more specific, since I am interested in the role of scientific practice for defining the land, I wondered how people argued about whether or not science was better for agriculture. I wrote a book about it. It's called Notes from the Ground: Science, Soil, and Society in the American Countryside. I commented here a few months ago that the book was finally on its way. Although Amazon sales do not begin until October 20th (here is their link), the publisher has it officially listed for…
rallain | September 23, 2009You know I like the Mythbusters, right? Well, I have been meaning to look at the shooting bullets in the air myth for quite some time. Now is that time. If you didn't catch that particular episode, the MythBusters wanted to see how dangerous it was to shoot a bullet straight up in the air.
I am not going to shoot any guns, or even drop bullets - that is for the MythBusters. What I will do instead is make a numerical calculation of the motion of a bullet shot into the air. Here is what Adam said about the bullets:
A .30-06 cartridge will go 10,000 feet high and take 58 seconds to come…
rallain | August 31, 2009Maybe this is a little old (in internet age), but it is a great example. Here is the Loop-the-loop stunt from the show Fifth Gear.
I like this. First, it is a bold stunt. But also, there is some good physics here. Though, most importantly, the Fifth Gear producers were kind enough to include a shot that was very compatible with video analysis.
I went to the official site of this stunt - http://looptheloop.dunlop.eu. From here I found some useful info:
Loop is 40 feet tall
The car is a Toyota Aygo
Some physics-y guy calculated that the car must go 36 mph to do the loop (I think that is…
rallain | August 28, 2009I found this in the most recent issue of The Physics Teacher (September 2009). Surprisingly, there were several good articles in this issue. One article discusses a doable version of the Millikan Oil drop experiment. Maybe you are not a (or were not) a physics major, so you might not be familiar with how cool, but tedious and squinty the oil drop experiment can be.
In the Millikan Oil drop experiment, small electrically charged drops of oil are placed in a constant electric field. It turns out that a small enough number of electrons are on each drop so that the quantization of charge can…
rallain | August 23, 2009I saw this video on digg or reddit. I can't remember which.
I was in awe. Then I started thinking. I wonder how fast that water was moving up right after the explosion. Too bad the video doesn't have a scale. Well, it kind of does - there is that ship. I am terrible at ship identification though. Maybe I can use my favorite scaling trick - assume the stuff is on the surface of the Earth. This means that free falling objects would have an acceleration of -9.8 m/s2. Let me try this on the water as it falls. Oh, trust me. I know it is not really free falling, but it is in this big…
rallain | August 12, 2009This Giant water slide video is extremely popular on the internets. Maybe you have not seen it (doubtful), then here it is:
This is such an incredible stunt that the very first question that comes up is - fake? or not fake? From my previous analysis, I can say:
Even though there is some slight perspective issues, the vertical acceleration seems to be constant and has a reasonable scale to give the acceleration of -9.8 m/s2
The horizontal motion is essentially constant (as a real jump would be)
The launch speed is about 19 m/s
The launch angle is 32.8 degrees
If the guy had no friction on…
rallain | August 6, 2009Thanks to Nick for showing me this video (Check out his blog - Fine Structure):
See more funny videos and TBT Videos at Today's Big Thing.
Wow. That was my first reaction. My second reaction was: no way. Is this real life? I just don't know. How hard would it be to find out exactly where to place that pool and where did they get the water from? Obviously, this one requires some analysis. First, on the VAS for this video: 4/8. Not too good. Oh here are the questions I would like to answer:
What is the guy's acceleration after he leaves the ramp?
What was his initial velocity leaving…
rallain | August 4, 2009Check this out (saw it on the interwebs):
It's this video inside a bus of a girl hitting the roof. My first thought was: well, she just jumped. But something was odd. She was in the air too long. Well, of course this calls for a video analysis (using Tracker Video Analysis). Actually, it is a good candidate for analysis. Primarily because the motion happens right next to the back of the bus and the bus can be considered the reference frame. The only problem is the scale. I totally guessed that the back window was 3 feet, but not sure this even matters. Here is the motion of the girl…
rallain | July 27, 2009Sciencegeekgirl is blogging from the AAPT. She talks about showing something interesting to get students thinking, and here is her example:
This reminds me of Dan Meyer's What Can You Do With This stuff. Anyway, I can't help it. I must analyze this video. Plus, Fran essentially threw down the gauntlet and called me out on this move. Another reason to analyze this movie is that it is obviously fake. Elephants are one of the few animals that can't jump. Not even a little bit. They don't like to have more than 1 foot off the ground. Ok, on to the analysis. As usual, I downloaded the…
rallain | July 15, 2009Note: This is a repost from my old site. Time to move it over.
First, what is different about motion on the moon and on Earth? Since the moon has a smaller mass in spite of its smaller size*, the moon has a smaller gravitational field. The gravitational field on the surface of the moon is 1/6th the field on the surface of the Earth. This means that the acceleration of a free falling on the object would be 1/6th the acceleration on Earth. So the question is: how would you change the time scale of a movie so that it looks like its acceleration is 1/6th of 9.8 m/s2?
*If you make the size of…
rallain | July 6, 2009July 4th can be fun. One activity my family enjoys is playing in the lake at my parents house. Along with this comes the jumping off the dock. Great fun, and great physics. Here is a short clip.
Work Energy Example from Rhett Allain on Vimeo.
Notice that I violated my own rules for making videos. In particular, the camera was not perpendicular to the motion. Also, I can handle panning cameras, but not when there is nothing but sky in the background. This video is therefore not appropriate for a video analysis. That is ok. I don't need it to talk about physics. So, here is the…
rallain | June 29, 2009I finally saw the movie Hancock. Yes, I know it has been out for a long time but I don't get out much. You know me, I can't leave something like this well enough alone. It's not my fault, I was born this way. It shouldn't spoil the movie too much if I tell you this one scene (you have probably already seen it anyway).
Basically, Hancock gets upset with this boy and throws him in the air to scare him or something. In case you did not time it, the kid was in the air for 23 seconds. I claim that in order for Hancock to throw a person in the air for this long, the acceleration during…
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 23, 2009This was on my 'to do' list, but Tom at Swans on Tea beat me to it. Basically, this grocery store has these plates that when depressed produce electrical energy. Tom does a good job pointing out that this is not free energy (the original article says this also). Clearly, the energy comes from the cars. How much would this cost the cars?
As always, let me start with some assumptions.
The original article says that the bumps will generate 30 kW of energy every hour. That is an odd thing to say. I am going to interpret that as 30 kW of power for all hours (every hour). They couldn't have…
rallain | June 22, 2009Note: This is an old post from the time before my blog was in wordpress. I noticed there was some incoming link for this, and I never moved it over. Here it is in it's unaltered (except for this part) format.
I don't know why I even suggest a new energy source. Fusion power is only a few years away in the future (just like it as always been). This will replace any other sources of energy that we could come up with. But, I can't help myself, I need to share my idea and save the world. It's what I do. (call me a superhero is you want).
We can get all of our energy from the rotation of the…