uncertainty
drorzel | June 3, 2011It's been a long and brutally busy week here, so I really ought to just take a day off from blogging. But there's a new paper in Science on quantum physics that's just too good to pass up, so here's a ReasearchBlogging post to close out the week.
Aw, c'mon, dude, I'm tired. What's so cool about this paper that it can't wait until next week? Well, the title kind of says it all: they measured the average trajectories of single photons passing through a double-slit apparatus. By making lots of repeated weak measurements at different positions behind the slits, they could reconstruct the average…
drorzel | May 11, 2011While Kenneth Ford's 101 Quantum Questions was generally good, there was one really regrettable bit, in Question 23: What is a "state of motion?" When giving examples of states, Ford defines the ground state as the lowest-energy state of a nucleus, then notes that its energy is not zero. He then writes:
An object brought to an absolute zero of temperature would have zero-point energy and nothing else. Because of zero-point energy, there is indeed such a thing as perpetual motion.
This is really the only objectionable content in the book, but he certainly made up in quality what it lacks in…
illconsidered | November 2, 2010Really great essay here, by Stephan Lewandowsky, on scientific uncertainty and manufacturing doubt.
rallain | August 24, 2010I might as well make a new tag called "basketball throws" because I can't stop with the analysis of these crazy basketball shots. Watch - in the end someone is going to post a video about how all these were faked (and I have said there is no clear evidence they are fake). Oh, if you want to see some shots that I am talking about - just search for Dude Perfect on youtube.
Physically, these crazy shots are possible. Time of flight in the video is comparable to a numerical model. But, the question is: how difficult are these shots? Are these one in a million? Are they easy? Are they…
grrlscientist | May 15, 2010tags: Richard Feynman Talks About Doubt, Uncertainty and Religion, science, imagination, religion, god, doubt, uncertainty, beliefs, Richard Feynman, streaming video
Physicist Richard Feynman talks about the improbability of the existence of a god, and his thoughts about the mythologies that form the basis of religion.
rallain | March 30, 2010This isn't much - really it is part of another post I am working on. The point of this post is to calculate the density of this piece of wood.
Really, there is a reason for this. I saw this little stick (sticklette?) and noticed that it was very cylindrically shaped. So, what if I just pretend it is a cylinder to calculate the volume? This way I won't have to get it wet or anything (because I might need this stick later).
First the mass
Yes, there is some uncertainty in the mass - but it is small. I put the stick on balance and I will use a value of m = 28.9 g or 0.0289 kg.
Volume
The…
rallain | March 13, 2010The most basic explanation of Pi is that it is the ratio of the circumference to the diameter for a circle. That seems simple enough, but it turns out that Pi is an irrational number - so you can't just write it down. Oh, I know that you are an uber-geek and you could recite the first 80 digits of Pi. But the question is - how many digits are enough?
In this post, I am going to assume that we don't know the true value of Pi (which is essentially true). I can then use propagation of error techniques to see how dependent different calculations are on the value of Pi.
Super Brief Intro to…
rallain | January 30, 2010After judging the science fair last week, I would like to revisit my tips for you the science fair participant.
Warning number 1
Some of the things I say here might go against what your teacher has told you. I am not sure what you should do in this case. Your teacher gives you a grade and I am just some dude on the internet. Proceed at your own risk.
Oh, and maybe you are a teacher. I think that is great that you are seeking more tips for your students. However, note that I have not read any science fair rules. I am merely thinking about science fair projects from a science viewpoint.…
rallain | December 30, 2009Some time ago, I wrote about the awesome things the Greeks did in astronomy. Basically they calculated the size of the Earth, distance and size of the moon and distance and size of the sun. The value obtained for the distance to the sun was a bit off, but still a bang up job if you ask me. (where bang-up is meant as a good thing) If the greeks were in my introductory physics lab, they would need to include uncertainties with their measurements. What would the uncertainty in the final value look like?
In my introductory physics lab course, I have students measure things and estimate the…
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 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 | 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,…
rallain | May 14, 2009I think the Mythbusters have a wonderful opportunity for educational outreach. Take this week's episode. One myth was to see if arrows fired from a moving horse penetrated more than arrows fired from a standing position. They first did this with real horses, but they said the data was not convincing.
I am pretty sure they had more than 10 trials recorded (there was a glimpse of the notebook). I would love to see this data and find (or let students find) the standard error of these measurements. This would be a great exercise to see how this whole uncertainty thing works.
As long as I am…
rallain | March 19, 2009I just got back from judging elementary level science fair (this is like kids in 6th grade or something). Here are some quick notes in no particular order.
Please, please do not have a 20 item list of supplies that you used on your board including things like thumb tacks, tape, paper and poster board. And then please do not read this list aloud during your presentation. I know you are nervous, I feel for you. Maybe you are trying to fill up time - maybe you think a long presentation is a good one. However, don't do it. Stick to the important stuff. If you need to fill up space on your…
rallain | March 16, 2009I previously talked about measurements (some) when I looked at the uncertainty in the distance to the Sun. One of the simple ways of determining the uncertainty of a calculated quantity is to use the uncertainty of the measured variables and find the max and min that calculated quantity can be. The example I used was in calculating the uncertainty for the area of a rectangle. So, the maximum and min areas would be:
And then the uncertainty in the area can be described as:
Yes, I know this is not as sophisticated as the normal procedure for error propagation, but it works. This is the…
rallain | March 4, 2009Some time ago, I wrote about the awesome things the Greeks did in astronomy. Basically they calculated the size of the Earth, distance and size of the moon and distance and size of the sun. The value obtained for the distance to the sun was a bit off, but still a bang up job if you ask me. (where bang-up is meant as a good thing) If the greeks were in my introductory physics lab, they would need to include uncertainties with their measurements. What would the uncertainty in the final value look like?
In my introductory physics lab course, I have students measure things and estimate the…
rallain | February 12, 2009Previously, I talked about science fairs. One of the problems is that students don't really have a good understanding of data analysis. For me, statistical analysis is just something to do with data. It isn't absolutely true. So, it doesn't really matter that students use sophisticated tests on their data. The important point is they use some type of test to compare data.
I just made up some arbitrary data analysis rules. Maybe if students and judges accept something like this, it could really improve science fair projects and judging.
To explain my analysis, I decided to have my own…
rallain | September 12, 2008Suppose I am working on a problem and I wish to calculate the density of something. I measure the mass to be *m* = 24.5 grams and the volume is *V* = 10 cm3. In this case the density would be:
ALERT! ALERT! ALERT! This is not a test!!!! Something is drastically wrong! Clearly I messed up. How can I have the mass measured to **3** significant figures, the volume measured to **1** significant figure, but the density calculated to **3** significant figures? Isn't this a violation of some fundamental…
esiegel | May 13, 2008There is a very techincal paper this morning by Martin Bojowald that asks the question, How Quantum Is The Big Bang? Let me break it down for you.
If you took a look at empty space and zoomed in on it, looking at spaces so small that they made a proton look like a basketball, you'd find that space wasn't so empty after all, but was filled with stuff like this:
What are these? They're little pairs of matter particles and anti-matter particles. They spontaneously get created, live for a brief fraction of a second, and then run into each other and disappear. That's what happens on very small…