Washing Cups

Only... two more blogs left? *cries* How is this possible?!?! I feel like I have to think of some really awesome blog topic to sum up the year, but all I could think of was cups...

A few days ago, I was washing dishes in hot water and soap. I like to stack them in the sink, especially the cups, after I get them all sudsy. :P However, when I began to rinse them out, I realized I couldn't separate two of the cups. THEY WERE STUCK. O_o. Frantically, I tried to pull them apart, but to no avail... the cups won the battle. Defeated, I left them in the sink (like a coward) for my dad to deal with when he got home.
Later, when he came home, he asked me why I'd left two cups in the sink. He seemed puzzled when I said that I couldn't separate them, because he said that he'd simply pulled them apart.
There were two solutions to this mystery. One was that I was just extremely weak, and the other, slightly more probable one was... PHYSICS! (The answer to everything!)

When I washed the two cups with hot water, they heated up and expanded. However, the inner cup was hotter than the outer one, because I washed it later, and then the outer cup acted as an insulator, keeping the heat in. The outer cup was constantly splashed with colder water as I rinsed the other dishes, cooling it. This means the inner cup expanded more than the outer one, and got stuck inside. The surfaces were then so close together that the static friction force was greater than the force of me pulling them apart. When the cups cooled down again, as they had by the time my dad came home, they were back to their normal sizes and were easy to separate.

Random Pop Gun Thing

Yes, a very creative title, I know... Sadness... only a few blogs left... *sniff*
So on Friday, while carrying my brother's various prizes while he bounced maniacally in a bounce house at the fair, Bean and I discovered the massive fun involved in this particular little toy. Who would have thought it would be so addicting? :P The gun works because of pressure, and also exhibits projectile motion of a sort, so naturally the first thing I thought of was physics...
To "load" the gun, you pull back on the handle, which applies a tension force on a string and causes a net force which equals ma (mass of the cork * acceleration) to accelerate and wedge itself into the hole at the end of the gun. When the handle is quickly pushed together again, the volume rapidly decreases, and using the rule PV = nRT, since the number of moles, temperature, and constant R stay constant, when V decreases, P must increase. Finally, the P increases enough that this force overcomes the static friction between the cork and the edges of the hole at the end of the gun. When this happens, the cork flies out, increasing the volume and decreasing the pressure. The cork then follows projectile motion, continuing with constant X velocity (assuming no significant air resistance) and accelerating downward at a rate of 9.8 m/s^2, until it reaches the end of the string and is yanked back by the tension and falls. The cork then hangs at equilibrium, with it's mass balanced by the tension in the string.

I've just noticed that the little kid in the video seems to be mesmerized by Bean repeatedly popping the pop gun... XD

Wireless Router

On Friday, I helped fix the robot which had been unfortunately broken by some overethusiastic robot *coughwaialuacough*.  However, that's not what I'm talking about in this blog.

As we tested the robot and drove it around, we used a wireless router, shown above, to connect the driver's station computer to the robot wirelessly.  There was a router attached to the driver station, and an antenna receiver on the robot itself which was connected to the CRio, the onboard computer on the robot.  The robots use WiFi to communicate, which uses 2.5 gigahertz frequency electromagnetic waves.  If you use the equation c=lambda*f, you can calculate the wavelength of the WiFi as 0.12 m.  This means the WiFi can fit through pretty small gaps and this explains how you can get WiFi signal from pretty far away.  However, over a long distance the protons experience scattering.

FRC Robotics!

Last weekend, I was at the FRC (FIRST Robotics Competition) at Stan Sheriff Center. Our team, 2438, did pretty well, and ended up in the finals, and although we didn't win, we got eliminated after losing to the winning alliance.
Here is our robot.Credit to Lauren Faris who was doing field reset stuffs, so she was close enough to take decent pictures.
Pretty! Shiny! (This is sounding strangely like Vicky, so I'll stop now...)

Obviously a lot of physics (and fun) is involved in building a big metal hundred pound robot. The part that I'll focus on today (so that I can stretch out robotics over several different blogs) is the balance of the robot. It's really important that the center of mass be as close to the center of the robot as possible, so that our robot is stable and will not flip over. As proof of the skillfulness of this, our robot was never flipped in a match, as many others were. While building and designing, we occasionally checked to see if there was more weight (mg!) in the front or back of the robot. When we tried to figure out where the battery should be placed, we balanced the robot on something to see if it wanted to tip further forward or back. Eventually we decided to mount the battery straps in the back to balance out the weight of the kicker in the front. Our robot was also low to the ground, and this meant that the center of mass was lower and so the robot wanted to stay in static equilibrium.