# charge

### The Strong Force for Beginners

"I found I could say things with color and shapes that I couldn't say any other way -- things I had no words for." -Georgia O'Keeffe When it comes to the Universe, it isn't just the stuff that's in it that's important. Image credit: 2MASS Extended Source Catalog (XSC). It's also how all that stuff interacts with itself and everything else. To the best of our knowledge, there are four fundamental forces in the Universe, and they're all essential to our existence. Image credit: Stichting Maharishi University of Management, the Netherlands. Some of them are familiar, like gravitation. On the…

### Basics: Electric Potential for a Point Charge

Pre Reqs: electric potential, electric field, work-energy To start, remember that for a constant electric field the change in electric potential energy would be: WARNING: that is only for a constant electric field. I know you will be tempted later to use this for a different electric field, but DON'T DO IT. But if not that, then how do find the change in electric potential for a point charge? Let me start with a conceptual question. Suppose there were two point charges, both positive but one is held in place. If I hold the other point charge a distance r away from the other charge and…

### Basics: Electric Potential

Pre Reqs: Electric Field, Work-Energy, Potential Energy If you are already familiar with the topics listed in the pre-reqs above, this will be uber-simple. Potential energy - short version The work-energy principle basically says: In this most basic form, the energy is just kinetic energy (if you are not going near the speed of light). BUT...if you have a force that is conservative (meaning the work done does not depend on the path you take), then you can make it a potential energy and move it to the other side. Warning: you can not have a force and have that force do both work AND be a…

### Basics: The electric field

Suppose I take a 1 kg ball and hold it near the surface of the Earth. What would be the gravitational force the Earth exerts on this ball? And I could say "g" is: The magnitude of this force would then be 9.8 Newtons. And, if I replaced the ball with a 10 kg ball, the force would be 98 Newtons. What does this have to do with the electric field? Well, you are probably already familiar with this idea of the gravitational force. Guess what? "g" is the gravitational field. Basically, it is the force per unit mass due to the Earth. This is only approximately constant. If I get very far…

### Basics: The Electrostatic Interaction

Pre Reqs: vectors, forces This is typically the first topic in the second semester of introductory physics - the interaction between objects with electric charge. There are 4 fundamental forces that physics typically looks at: Gravity - an interaction between objects with mass - wow, I don't have a post on the universal law of gravity? Electromagnetic - an interaction between objects with electric charge. Weak Nuclear - an interaction between (let me just say for simplicity) leptons. Strong Nuclear - an interaction between hadrons. I know those last two are complicated - but I am not going…

### 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…

### What kind of electricity is lightning?

Someone complained about a teacher using this question and the answer was disputed. After some time, the teacher claimed that the answer was that lightning is static electricity because she looked it up on the internet. So, I decided to look also, here is what I found searching for "what kind of electricity is lightning?" in google: Electricity Facts - Dialogue for Kids (Idaho Public Television) A couple of complaints about this site: First, I am not fond of the term "Science Facts". What is a science fact? Something that is proven true? This really is not how science works. Second, I am not…

### Big News about Black Holes!

This has been all over my inbox since the press release came out yesterday; it's been on slashdot (thanks Brian), it's been at space.com, and there's a mediocre writeup on Universe Today. What's the big news? Black Holes don't destroy information after all! What is this whole information thing, anyway? Take a look at all the normal stuff in the Universe: photons, protons, neutrons, and electrons, for example. They have lots of different properties each. They move around one another, they get bound and unbound from one another, they exert forces on one another, etc. They're aware of one…

### Will the LHC Create Dark Matter?

Hector writes in and asks about someone from Sheffield in the UK who says that the Large Hadron Collider (LHC) will create Dark Matter: The massive ATLAS detector will measure the debris from collisions occurring in the Large Hadron Collider (LHC) which recreates the conditions found in the early universe during the Big Bang when Dark Matter was first created. If the LHC does indeed create such particles then it will be the first time that the amount of Dark Matter in the universe has increased since the Big Bang - the LHC will effectively be a Dark Matter 'factory'. Well, Hector basically…