Recent content by chrisbaird

Actually, the potential going to zero at infinity is just a convention to make the math easier. If you placed your system in a giant metal box (giant enough to be considered out at infinity) and held the box at a potential V, the problem would go to V at infinity and not zero. When you work with...

Static fields, by definition, don't propagate. If you have an initially static field, and a change occurs, you no longer have a static field. You now have a regular electrodynamic field and the change propagates out at the speed of light in the material just like all propagating electrodynamic...

An oscillating dipole cannot radiate along its axis (you can convince yourself of this by drawing a charge bobbing up and down with the electric field lines attached at different points in time). For the one polarization, the axis of the induced dipoles lines up with the reflected ray at...

Dark matter is the gravitational glue that keeps galaxies from flying apart. Without dark matter, most galaxies would not have enough mass to create enough gravity to keep it in one piece. Dark matter gives enough extra mass to do the trick. Dark matter is not just dust or gas. You can see dust...

A short circuit sends more current than expected to parts of the circuit, causing them to physically burn out as they are not designed to handle such a load. If you opened up the phone, you may even see burn marks and melted plastic on the circuit board. Replacing the burned out circuit...

If Earth were perfectly rigid, then yes, in principle, you spinning on a chair would cause the Earth to spin in the opposite direction to conserve momentum. But the Earth is so huge compared to you that the change in spin the Earth would experience is so small it would just get overpowered by...

No, you need the fields for a complete description of electromagnetic. The fields exist in their own right. How can you describe an isolated electromagnetic wave in free space without using fields? The force construction replacing the fields construction only works when you are talking about the...

Yes of course. I have in fact experienced this. I had a pedal bike with a headlamp that was powered by a little generator attached to the wheels. Whenever I turned on the headlamp, the wheels a little harder to push. Of course it should because you can't create energy out of nothing. I...

More accurately: The electric field in a perfect conductor at equilibrium is zero. There are no perfect conductors in real life, so the field always pokes in a bit. But this is an excellent approximation for many conductors. Also, you have to have perfect equilibrium to give all the excess...

It's called the law of conservation of mass/energy. Matter/energy cannot be created or destroyed, but only transformed into different states. The total matter/energy in a closed system must stay constant. That is what the equation means. The c is just to make the units work. In naturalized...

"I was always told that the physics of these ride designs made it so that the people would be safe even without a restraint." You were told wrong. That used to be true of many of the older, safer, slower rides. As an extra precaution, designers aligned the g-forces to keep a person in their seat...

sweet_springs: Gauge freedom is not a result of some kind of redundancy in Maxwell's equations for the fields, because there is no redundancy in Maxwell's equations for the fields. Gauge freedom is a result of the fact that we are defining the fields in terms of something else non-physical (the...

I know this thread is old but I have done some analysis and I need to correct my earlier comments. Maxwell's equations contain six unknowns: Ex, Ey, Ez, Bx, By, Bz and seem to contain a linear set of differential equations consisting of 8 scalar equations. The problem therefore seems...

- Suck all the air and dust out of a given volume and you have a classic "vacuum", but you still have solar neutrinos shooting through (among other things). - Shield the solar neutrinos (good luck), and you still have cosmic rays (among other things). - Shield the cosmic rays, and you still have...

The point is that cosmic expansion itself does not stop. Space itself is everywhere expanding, even here on earth. But as the Earth is bumped slightly father away from the sun due to cosmic expansion, it does not have the velocity to sustain a higher orbit, so it returns to its original distance...