rallain | May 18, 2009Another electric motorcycle post. (Here is the post on the wind-recharged drag racing motorcycle) This new one is a solar powered motorcycle. The site claims that the bike can go 50 miles on a full charge (from Gas2.org). This is easily possible, but how long would it take to charge with normal solar panels? Here is an image of the bike.
Questions to be answered: How much energy would the bike need to go 50 miles? How much power (average) could you expect to get from the solar panels? And...how long would it take to charge this sucker. I am sure you can store enough energy in a…
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 | 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…
rallain | May 12, 2009Maybe you have seen this trick. Basically, you hold by supporting it with two fingers from the bottom. You then move your hand around to keep it balanced while the stick is vertical. It is really not as hard as it looks. Also, there are two things that can make your job easier. Use a longer stick, or add an extra mass at the end of the stick. Here is a video of me demonstrating this. (I forgot, this also an event in the show Unbeatable Banzuke)
Balancing a Stick Demo from Rhett Allain on Vimeo.
So, how does this work? Let me start with a stick that is mostly vertical and supported by…
rallain | May 7, 2009Time Warp is this Discovery channel show that makes slow motion videos of stuff. Not too bad of a show (although I already talked about the samurai guy and "waves of energy").
Professor splash is this guy that jumps from really high positions and lands in 1 foot of water (and doesn't die). He was on Time Warp last night. If you are interested in this, I did an explanation of how it works in a previous post.
The Physics of Professor Splash's Jump into 1 foot of water
I haven't watched the whole show yet - but I did TiVo it. If there is any thing interesting to analyze, I will post that…
rallain | May 6, 2009I probably should have included this idea on my "All about science" blog post. Maybe I didn't put it in there because if I talk about what science is you can figure out what it is not.
Science is not math
Science is all about making models. It is true that many current models are mathematical models, but it doesn't have to be that way, and it hasn't always been that way. Think about rubbing a piece of metal with a magnet. It gets magnetized - right? What if you then cut that magnet in half? Then you have two smaller magnets. How can you make a model that explains this phenomena? Yes…
rallain | May 5, 2009I just realized that something has been bothering me. It is this KillaCycle - the electric zoom-fast motorcycle that I posted about previously. It clearly is super fast. However there are two claims that seem iffy.
It can be recharged in 4 minutes.
It is recharged by wind power.
It may be possible that these individually could be true - but could it be recharged in 4 minutes by the wind? I am not sure. Let me do some estimations to see if this is possible. What am I starting with:
From the review on gas2.org, uses cordless drill batteries.
Uses 1200 batteries
Produces 500 bhp - not…
rallain | May 4, 2009I got a great question (several actually) from the students participating in the Adopt a Physicist program. The question went something like this (not a direct quote):
Why is it that the stuff we study in physics class is 100 year old stuff?
I am sure the students phrased this better than that, but you get the idea. The first response is that most of the most of the topics covered in introductory physics is more like 300 years old (Newton). Needless, why do most course cover old topics?
First, to answer this question I would ask the following:
What is the purpose (goal) of the introductory…
rallain | May 2, 2009So, I am mowing the lawn. What to do better than thinking while I mow? Sometimes mowing is no fun. It is just a type of maintenance. How much of what we do is maintenance? I first thought about this when I was thinking about getting a new car. Wouldn't it be great if you didn't have to get the brakes changed or the tires rotated? I hate taking the car to the shop to get these things done (yes, if I was motivated I could do them myself). Here are some other maintenance things:
Mopping the floors
Paying bills
Keeping files organized on your computer
Brushing your teeth
How much of…
rallain | May 2, 2009There are a couple of things I should probably not talk about. One of them is photons. But no matter what you think about photons you will probably agree that this is not a very good description of electromagnetic radiation. (from comos4kids.com)
Structure of Energy:All EM energy waves travel at the speed of light when in a vacuum. No matter what their frequency or wavelength, they always move at the same speed. Some properties of waves, such as diffraction and interference, are also seen in EM radiation. Scientists have figured out that there are tiny particles in these waves. The…
rallain | April 30, 2009Announcement: There is a ton of extra money for education of teachers. You should submit a grant proposal.
Hey, let's submit a proposal and get laptops for a whole bunch of students.
To me, this is like giving morphine to people with the flu. It will make them feel better, but doesn't really fix the problem. A proposal like the above would probably get funded and probably make some people look great, but would it really help?
rallain | April 30, 2009ZapperZ already beat me to this, but if it is worth doing once it is worth doing again. Here is a video of an electric motorcycle that can apparently go from 0 to 60 mph in 1 second.
What acceleration would this have? If you want, you can look at my stuff on kinematics, but this case is pretty straight forward. Really, as straight forward as one could get. Let me start with the definition of acceleration: (in the x-direction since this is a 1-d problem)
I know both the change in speed and the time, so this is easy. I can make it even easier using google. The acceleration is 60 mph/s.…
rallain | April 28, 2009In the second Cat in the Hat book (I think it is the second one), the Cat reveals that he has more smaller cats under his hat. They are labeled A - Z with Z being so small you can't even see. Question: What is the sequence of sizes for successive cats? How big would Cat Z be?
Here is the first picture that Cat reveals Cat A. It is not trivial to measure their relative sizes because they are in different positions. I drew two circles, one around each head and looked at the circle sizes.
So, Cat has a head that is 165 px tall and Cat A has a head 61 px tall. Let me call the total length…
rallain | April 26, 2009It's odd that I have talked about these forces so much. First, I talked about how centrifugal forces were not real and the difference between centrifugal and centripetal forces. Then I talked about how sometimes, fake forces are good. Finally, I talked about the origin of the words centrifugal and centripetal. (note: "talked about" means wrote a blog post)
In thinking about centripetal forces, I realized that I could come up with a situation in which the centrifugal force is the centripetal force. This is great. I can end all the confusion between centrifugal and centripetal by making a…
rallain | April 24, 2009A student in my office temporarily confused the words centripetal and centrifugal. This started me thinking about these two words. They mean different things, but do sound and look similar. I have previously talked about the difference between fake and non-fake forces, but let me quickly define these two:
Centripetal: This is the force needed to make something move in a circle. The force could actually be a number of things such as: friction, gravity, tension in a rope or any combination. Centripetal force is a name for a real force that has the role of making something move in a circle…
rallain | April 24, 2009I have already indirectly talked about this before, but I see it more and more. Say you have a show. It has to be more than entertaining, it has to educational. How do you make things educational? Describe the physics behind the concepts - right? Fine. How do you explain stuff? It's simple. Just make some diagrams with arrows. Be sure to use words like "force", "velocity", "acceleration". You know, physicsy words. Everything will be fine.
Everything will not be fine. First, I love MythBusters. They are awesome. I know they are not scientists, and that is maybe why I like them.…
rallain | April 22, 2009Some time ago I was looking for materials to possibly build a foucault pendulum. Of course the first step is google. There was a site that suggested two old issues of Scientific American, and it happens that we have tons of old Scientific Americans in the store room. I found the two that I needed. I will talk about foucault pendulum in second, but let me show this picture.
This is a device to prevent elliptical motion of the pendulum. Part of it has a ring of nickel. Now for the quote:
"The nickel ring, perhaps appropriately, should have the dimensions of a U.S. five-cent piece, with a…
rallain | April 21, 2009I am not sure if First Excited State posted this as a blog entry, but it was mentioned on twitter. Question: why are sparks blue? My first gut response was that this is the blackbody color. Wrong for several reasons. The short answer is that sparks are blue because of the colors given off from nitrogen and oxygen when they are excited.
In order to make this post longer than necessary, let me say something about blackbodies. A blackbody is an object that emits radiation due only to it's temperature. Since it does not reflect anything, it looks black at room temperatures. You can make a…
rallain | April 21, 2009First: Car Talk is awesome. I wish I could come up with some class activities that help students become as good at trouble shooting and critical thinking as Tom and Ray are. Anyway, they are quite entertaining.
So, my Dad called and told me he heard a discussion on Car Talk about the effect DC to AC converters and accessories plugged in to it and how they would effect gas mileage. I skimmed through the last Car Talk podcast, but couldn't find it. He must have heard a re-run on the radio or something (he doesn't really believe in podcasts). Let me calculate the effect a number of things…
rallain | April 16, 2009I have been meaning to write about this for quite some time. Really, I wanted to reply to Chad's article on science at Uncertain Principles, but you know how things go. So, here are my key and interesting points about science in random order.
Science is all about models (not ball bearings)
Science is about making models. What is a model? A model can be lots of things. It can be a mathematical relationship, a conceptual model, or even a physical model. One model I like to use is static friction. For many cases, the frictional force can be modeled as:
This model says the frictional…