Measuring gravity with Kater's Pendulum

First off, let me describe how this Kater's Pendulum (shown in the adjacent picture) is supposed to work. There are two pivot points (a), one at each end. At one end there is a major weight (d) and at the other end a minor weight (b & c). The minor one is adjustable, and by moving it in or out, the period (the rate at which the pendulum swings) can be changed. So, what you do with this thing is hang it from one pivot and time the swing, then flip it over and time it again, moving the minor weight in and out until the two times are the same. Moving the minor weight counter-balances the major one and makes the whole thing effectively an 'ideal' pendulum.

Knowing the distance between the pivot points and the time of the swing, we can use this formula to get the value of gravity at that point. Of course Tom isn't going to be using a calculator over there, so all he's going to do is collect the numbers at various points and bring them back to Frank to do all the number crunching.

It turns out that Frank just happens to have a museum-quality piece that he's going to let Tom take through the Door to do some testing. It wasn't designed to be portable at all, so Frank has to make some modifications to the frame where Tom will be hanging the thing. Frank also has a set of hourglasses (though they really should be called minute-glasses) that Tom will be using as timers. I'm not certain if Tom (or ANYone for that matter) will have enough patience to do all this stuff. Those physicists must have been really dedicated to their field of study to invent stuff like this.

We'll see what we have to report next week. Until then, keep swinging!

Photos examined by astromers, and the core of the planet isn't iron

Well, the photos have been developed and most of them were quite good. Turns out Tom is fairly handy with a camera. Frank has sent the pictures off to an astronomer friend of his, and we hope to have some kind of estimate of the planet's location soon. Most of the pictures looked very much as we expected (see the adjacent picture from an amateur photo site). The only thing Frank has been able to determine from them so far is the rotation of the planet. Doing a calculation using the length of the star streaks and knowing the shutter speed, Frank says that a 'day' on the planet is a bit less than 32 hours. Much longer than here on Earth, but Tom says that it doesn't feel longer; he just has more time to get things done.

The fact that a 'day' is longer there can be the result of a couple different things. Either the planet actually rotates slower, or it has a much larger diameter. A larger planet should have a stronger gravitational field, but only if the composition is similar to Earth's. From the lack of magnetism over there, Frank has hypothesised that the planet is lacking the iron core that forms the basis of Earth's magnetic field, so although it might be larger, it has less mass. In other words, it is less dense.

So, based on his guess about the core, Frank's next experiment is going to test the exact gravity there, using a Kater's Pendulum. I suggested that he also measure the size of the planet the same way Eratosthenes did, but he just laughed. Apparently we'd have to explore a bit more of the planet to be able to get measurements like that.

BTW we can't just keep calling it 'the planet', so Frank thinks we should name it, but I'm certain that the natives already have a name for it. We just need to ask them. What do you think? Let us know in the survey.

I'll report on it next week.

Happy Birthday to the IBM PC (and what about Apple?)

Well, Frank has yet another anniversary to celebrate today. It's been 30 years since the IBM PC was released, and THAT was a step in the right direction. Of course, he's quick to point out that Apple beat IBM by four years when they released the Apple ][ in 1977. (I think Frank still has an old Apple ][ in the back of his closet, though he'd never admit it in public. In fact if he does have one, I know he'd never sell it.)

Back in those days, IBM kept most of the technical details close to the chest, if not outright proprietary, and Apple's reference manual not only had a schematic that folded out, but it also had the source code of the Monitor ROM (what is now known as the BIOS). Times have certainly changed since then, what with Apple keeping all the secrets and IBM being so open that just about anyone can build an ISA compatible board to expand the capabilities of a PC.

Well, enough reminiscing, we've got work to do. Next week. Same bat time, same bat channel.

Developing REAL film: a REAL task ahead of us

We had a bit of a difficulty getting the pictures Tom took of the stars developed. Do you know how few places are available that can take real film and make pictures? Yes, I know that may local stores can make prints, but almost all of them only handle digital pictures, which obviously won't work for us. In our case the decision was made easier by the fact that Frank is a bit paranoid about keeping the details of the Door secret (he's right to be concerned about industrial espionage). The decision was easier, but the results of that decision just made more work for us: Frank decided that it would be better to process the film in house.

Frank gave me a list of the chemicals needed, and whilst I was procuring them, he built a light-tight tank that would do the trick. BTW, this is not a procedure that I'd recommend to anyone who isn't seriously into doing things on your own.

Well, I've clearly got my work cut out for me, so I'll call it quits for now. See ya in a week.