demo
rallain | September 10, 2010Here is the next item.
There is a threaded plug on the top. I took it off so you could see inside. The whole thing is pretty heavy.
Good luck, and let's be careful out there.
rallain | September 8, 2010Actually, it should be called Happy "Magnitude of the local Earth gravitational field" day. You know, 9.8 N/kg on September 8 (9/8). Get it? Well, the idea was for the physics students and faculty to build some stuff to do outside - projectile motion type stuff. Well, we had the idea a while ago and then kind of forgot about it.
In order to just get something done, I set up the "shoot the falling target" demo. (previously known as shoot the monkey). Here is a quick video demo (seriously - first take too).
What is going on here and what does this have to do with g? Well, it doesn't…
rallain | September 7, 2010Congratulations Fran. Not only did she answer the "What the heck is this?" correctly, she was the first commenter.
Here is the original item:
It is of course a gas discharge tube. You put these tubes in there (as shown above) with helium or neon or whatever in there and it excites the gas to give off light.
Honestly, we have like 10 of these things laying around. Some of them are newer and say "Danger 5000 volts"), but these older ones say nothing. Here is an example of one of the first ones I saw.
I didn't figure out what it was for a while because most of the ones we have don't have those…
rallain | September 3, 2010Please note the official change of the title of this game, it is no longer "what is this".
Here is the item:
I suspect someone will know what this is. Honestly, I didn't figure it out right away. However, I have found that the readers as a group generally are more knowledgeable than me by myself.
Oh, I don't think there is really much description to add here. I included a meter stick for scale.
P.S. How come a device for measuring temperature is a thermometer and a device for measuring electric potential is a voltmeter? Shouldn't the meterstick be called either a length-meter or a meter…
rallain | August 31, 2010Reader Fruity was the first to correctly name this device - on just the 9th comment. Impressive. Honestly, when I found this thing I had no clue. I asked other physicists and none of us were sure. However, I did find the answer. Let me show you my secret.
I don't know how old this thing is, but it is old. When I open it, my nose and eyes get all tingly - probably from the mold. Here is that apparatus in the book (tome):
I can't show you the whole page because it has other stuff of awesomeness that I want to show you later. But, I can show you the description for that item.
I am…
rallain | August 27, 2010Here is my plan. Post a "what is this" on every Friday until I run out of things. I will post the answer on Tuesday. Maybe we should start keeping points. You get more points for being the first one to get it right. You lose points for getting it wrong.
Last week was easy, but I think this is more of an appropriate level. Here it is:
Nice - it has a tag, but no part number. Honestly, this one stumped me for a while. If you have any reasonable questions, I might answer them.
rallain | August 24, 2010Perhaps you have had enough time to think about the first "What is this" demo item. Here is the item in question.
It seems most of you were right on track with this one - probably because you can still buy such a device. This thingy launches a small ball horizontally while at the same time dropping a ball. It is supposed to show that the vertical and horizontal components of an object in projectile motion are independent.
It takes two balls (which I didn't have when I took the picture). One ball goes on each end and the arm is pulled back.
Update: Thanks to Kevin and Frank for pointing…
rallain | August 21, 2010Let's play a game. I think this will be fun. So, a couple of years ago I had the duty of organizing the physics demo room (well, "demo" is maybe not the best term). This room is quite large and there is a whole bunch of stuff in here, some of the items are very old.
There were lots of items that I knew exactly what they were. But, there were other items that made me go 'huh?'. So, here I will post an item. You post a comment regarding what you think it is and what it is used for. Some of these items I know the answer to, some I do not. Some of these pictures might just be part of a…
rallain | July 11, 2010My car had a flat tire. When you get a flat tire, you might as well make something useful of it - right? As I was jacking the car up, I had a great idea. Use this for one of my "Spoof Science" videos. The only problem is that this takes a ton of work to put together a short video. So, I am just going to talk about what I could have done.
Here is a quick clip of my 4 year old lifting the car.
So, he lifted the car - it maybe be difficult to tell, but he did. HE LIFTED THE CAR! Ok, I know, he only lifted part of the car. If I were to use this in a real Spoof Science video, I would have…
rallain | June 27, 2010Sometimes I get asked to do some demos for kids. I like this, it is fun. This week, I was asked to do just such a demo. Kind of as a historical record, I am going to document what I did.
The audience
It is always important to think about who you are talking to. Is this a group of high school physics students? High school teachers? Middle school teachers? Kids? It could be anything. In this case, I was meeting with a group of kids from ages 8 to 12 as part of a science camp.
The Objective
Is there a reason for the demo show? In this case, there was no stated objective. That means I can…
rallain | May 13, 2010Yes, green laser pointers are cool. Especially when you use them to make stuff fluoresce. Ok, what about a blue laser pointer? They are getting surprisingly cheap (Amazon has a 10 mW for pretty cheap). Still not cheap enough for me. But, you know what? Some of the physics majors here at Southeastern Louisiana University purchased a couple of these. Physics major Daniel let me borrow his.
First, they don't look too bright. This is probably because our eyes are not too sensitive to this wavelength. The blue 10 mW does not look anywhere near as bright as the 5 mW green that I used in…
rallain | May 5, 2010I was going to make this as a video tutorial, but it just didn't work out right. So, here it is in blog post form.
How do you deal with a video that zoom and pans at the same time? You could keep on adjusting the coordinate axis AND adjust the scale for each frame - but sometimes that is not possible. Tracker Video has a great tool to handle these types of videos - the calibration point pair. The basic idea is that you identify two points in a scene that should be stationary (part of the background) and track those two points. Tracker will then adjust the coordinates and scale to make…
rallain | May 4, 2010So you have seen these color filters (or gels as they are also called). When you look through a red filter, everything looks red. What do they do to the light? I am not going to tell you the answer. However, I will show you some examples so that you can figure out the answer yourself.
In this video, I am going to use a red and a green laser pointer. The nice thing about laser pointers is that they essentially create only one color of light.
rallain | May 4, 2010It is my duty as a blogger to mention lasers in this time of international laser celebration. This May is the 50th anniversary of the first lasers. Everyone knows a laser that they love, right? We all use them. So, instead of talking about lasers, I am going to post some great links to other laser stuff (including some of my stuff).
the history of the first lasers (AIP)
The above is the American Institute of Physics's presentation of the history of the laser. Really, this does a great job of giving all the details you would want. I highly recommend it.
Uncertain Principle's Laser…
rallain | April 12, 2010This was a great question. When you come inside after playing in the sunny outside, why is it so dark?
Simple answer: because your eyes are smart. When you are outside, there is a lot of light. Really, it is too much light. To compensate for this, your pupils (the part of your eye that light goes through) closes some. And then, when you go back inside your pupils are still small. Inside (even with the lights on) is not nearly as bright as outside. Not enough light is getting through your pupils and so everything looks "dark".
Here is a simple demo. While inside, take a flashlight (not…
rallain | April 7, 2010Check out this video demo:
So, that is just plain water. If I am careful, I can make that thin aluminum disk stay on the surface of the water. This is not the same as floating in Archimedes principle. It is different. This is staying on the surface because of surface tension.
Bouyancy
I think my best explanation of buoyancy was in the post about MythBusters floating a lead balloon. But, basically for buoyancy there is an upward force from the water on the thing that is floating. If I want to explain this in terms of the particle model of a gas or fluid, I could say that the particles in…
rallain | March 26, 2010I am surprised at how many people (chemistry faculty included) have never seen this demo. (oh, technically it is called a cartesian diver demo) Basically, you put some floating object that has an air space in a closed bottle of water. When you squeeze it, the diver goes down.
For my setup, I used a glass eye-dropper. Put it in a cup to make sure it just barely floats and then put it in a completely full water bottle. If you don't have a eye-dropper, you can use anything that floats with an air space. I have done this with part of a straw before. Fold a small section of a straw in half…
rallain | March 24, 2010How does a suction cup work? It is all about the atmosphere. Here is a demo. Take some type of "suction cup" device. In this case, I used a toy dart. Stick it to something smooth and lift it up. Like this:
What lifts up the metal block? The atmosphere. Diagram time:
But this isn't a very realistic diagram. Actually, the suction cup would be pushing down on the block because the force from the atmosphere would be too large to balance with the weight. Let me put some numbers in here. Suppose this is an aluminum block - I just going to pretend it is 4cm on a side (and a cube). In…
rallain | March 14, 2010Oh, I know you missed it. Really, it wasn't your fault. Pi day fell on a Sunday, so how are you supposed to have pi-day activities in class? Don't let it stop you. You are better than that. Do the activity anyway. What to do? Here are some suggestions. (Suggestions aimed mostly at the high school level)
Plot Diameter vs. Circumference
This is a great one. Let your students find as many round things as they can (cylinders work the best - or flat stuff). Measure the circumference (you can use a string or a tape measure) and the diameter. Since the relationship between these two is…
rallain | March 8, 2010Hat tip to Frank for sending me a link to this video:
If you have never done a demo like this (without the motorcycle), you should. It really isn't too difficult. Here is a video of my version:
Inertial demo from Rhett Allain on Vimeo.
So, the question is: is the motorcycle thing real or fake?
First, let me talk about the key aspect of this demo. Why don't the glasses move? Well, they move - but just not very far. The demo is supposed to be an example of Newton's Second law, or you could say it is the momentum principle (which is what I will use). If a force is applied for a short time…