# buoyancy

### The Physics of a Sad Balloon

My birthday was two months ago, and SteelyKid's was the weekend before last, so we've had balloons running around the house for a good while now. Meaning that when I came into the library yesterday, I saw the sad little image on the right: a half-deflated Mylar balloon floating at about chest height. Now, the first thought of a normal person on seeing this would be "Why didn't we throw this away a while ago?" My thought, since I've been on a bit of an everyday physics kick for a little while now, was "Hey, physics!" "What do you mean?," you ask. "What physics is there in the sad balloon? It…

### Heavy Heavy Water

I make an effort to say nice things about pop-science books that I read, whether for book research or blog reviews. Every now and then, though, I hit a book that has enough problems that I have a hard time taking anything positive from it. I got David Bodanis's E=mc2: A Biography of the World's Most Famous Equation from Union's library because I like the subtitle, and plan to reference it in the relevant chapter of the book-in-progress. I figured that, if I'm going to swipe his subtitle, I should at least be able to say something substantive about the book. Bodanis takes pains to say that…

### Speed of a rising drop of oil

The oil spill is still in the news (sadly). One thing that keeps coming up is the speed that the oil bubbles rise to the surface. This is important in different oil-capture methods. The common statement is that smaller bubbles of oil can take quite a long time to reach the surface and larger bubbles can take about 2 days. This is one of those cases where things do not scale quite the same. Suppose there is a spherical oil bubble rising at a constant speed. Here is a force diagram for such a bubble: If this drop is going at a constant speed, then all these forces have to add up to the…

### How big of a balloon do you need to get to 120,000 feet high?

I am still thinking about the Red Bull Stratos Jump. Sorry, but there is just tons of great physics here. Next question - how big of a balloon would you need to get up to 120,000 feet? I am not going into the buoyancy details of Archimedes Principle - I think that was covered fairly thoroughly with the MythBusters floating lead balloon. However, in short, here is a force diagram for a floating balloon. For a floating balloon, the buoyancy force must equal the weight of the whole thing. It turns out that the buoyant force is equal to the weight of the gas (or fluid) the object displaces…

### Hey, look kids! There's Big Ben.

And there's parliament. Ok - sorry, I had to make a "Tom (Swans on Tea)" title for this one. Tom, forgive me. Here are two great circular motion videos. First, this one is from Dale Basler. He made himself a fine little floater-type accelerometer. Better than just make it, he made a video of the accelerometer in his car going around a round about. Check it out. Bobber Meets Roundabout from Dale Basler on Vimeo. So, if he is driving at a constant 10 mph, how big is the round about (traffic circle)? Next video - more silly kids First, I saw this one on ZapperZ's Physics and Physicists who…

### Surface Tension vs. Floating

Check 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…

### Diver in a bottle

I 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…

### Pressure demo: suction

How 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…

### RP 5: MythBusters: How small could a lead balloon be?

On a previous episode of The MythBusters, Adam and Jamie made a lead balloon float. I was impressed. Anyway, I decided to give a more detailed explanation on how this happens. Using the thickness of foil they had, what is the smallest balloon that would float? If the one they created were filled all the way, how much could it lift? First, how does stuff float at all? There are many levels that this question could be answered. I could start with the nature of pressure, but maybe I will save that for another day. So, let me start with pressure. The reason a balloon floats is because the air…

### RP 4: More on the movie Up! (or Upper)

So, analysis of the movie Up is pretty popular in the blogosphere. Figure I might as well surf the popularity wave. So, I have a couple more questions. The most important thing to estimate is the mass of the house. I am going to completely ignore the buoyancy of the house. I figure this will be insignificant next to the buoyancy needed. Anyway, let me go ahead and recap what has already been done on this in the blogosphere. Wired Science - How Pixar's Up House Could Really Fly - from that post: First, they calculated (seemingly correct) that the buoyancy of helium is 0.067 pounds per…

### Lab: The Charge of an Electron

Not really. Here are the details (and some data) for the Millikan Oil Drop Experiment without the oil drop that I talked about previously (originally from The Physics Teacher - lucky you, it was a featured article so it should still be available (pdf)). The basic idea that Lowell McCann and Earl Blodgett from U of Wisconsin propose is to do an experiment similar to the oil drop experiment, but not so squinty (if you have done the oil drop experiment, you know what I mean). Instead of dropping charged oil in an electric field, they drop containers with metal nuts in water. The goal is to…

### Millikan Oil Drop without the Oil

I 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…

### More on the movie Up! (or Upper)

So, analysis of the movie Up is pretty popular in the blogosphere. Figure I might as well surf the popularity wave. So, I have a couple more questions. The most important thing to estimate is the mass of the house. I am going to completely ignore the buoyancy of the house. I figure this will be insignificant next to the buoyancy needed. Anyway, let me go ahead and recap what has already been done on this in the blogosphere. Wired Science - How Pixar's Up House Could Really Fly - from that post: First, they calculated (seemingly correct) that the buoyancy of helium is 0.067 pounds per…

### Physics and the movie UP - floating a house

I 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…

### 'Weapon Masters' doesn't understand floating

There is this show "Weapon Masters" - I think it comes on the discovery channel. It is not a bad show. The basic idea is that they have this history guy talk about the historical aspect of some type of weapon and this other guy tries to make an improved version. Last night the goal was to recreate the original flame thrower mounted on a boat. They found a boat and they needed to test it's sea worthiness. The builder guy (sorry, I don't know his name) estimated that they would have 1000 lbs of equipment in the boat. To simulate this weight, they put 4 guys and two barrels of water in…

### MythBusters: How small could a lead balloon be?

On a previous episode of The MythBusters, Adam and Jamie made a lead balloon float. I was impressed. Anyway, I decided to give a more detailed explanation on how this happens. Using the thickness of foil they had, what is the smallest balloon that would float? If the one they created were filled all the way, how much could it lift? First, how does stuff float at all? There are many levels that this question could be answered. I could start with the nature of pressure, but maybe I will save that for another day. So, let me start with pressure. The reason a balloon floats is because the air…

### Stealthy alligators dive, rise and roll by moving their lungs

Crocodiles and alligators are the epitome of stealth. They can wait motionlessly for prey on the surface of the water, dive to the bottom, or roll around the length of their bodies, all without creating a single ripple. This sneaky manoeuvrability is all the more impressive for the fact that a crocodilian can pull it off without moving its legs or tail. It's particularly difficult because a waiting crocodilian has to move slowly and methodically, and must make do without the helpful forces of lift and drag that accompany faster movements. Now, for the first time, we know how they do it. They…