I was not content with the larger weight bag that was included in the Gravity Light kit. It’s too long and takes up a lot of room. By making it smaller I may be able to get the Gravity Light to run for up to a minute longer. I filled it with rocks which are pretty heavy, but they still take up the whole bag. I thought what I needed was a smaller piece of a much denser material. I went online and found tables of the densities (specific gravities) of common materials. One table listed the density of rock as somewhere around 2.8. That means the cubic centimeter of rock weighs about 2.5 to 3 times that of a cubic centimeter of water. Another table of the elements listed iron as having a density of about 7.8. Wow! That’s more than twice as heavy as a rock of the same size! It also listed the density of lead which is more than 11!
A few years ago I had a problem: I put a CFL light into a gooseneck lamp and it wouldn’t stay upright, it was too top heavy. I went to Walmart and bought a two and a half pound weight for a barbell. I screwed that to the bottom of the lamp and everything was fine. So I put this on my to do list: go to a store or Walmart and check the prices of barbell weights. They are made out of cast iron which is 7.8 X as heavy as water.
As the bag hangs from the gravity light, it has to hang a certain way so that it doesn’t get caught up in the small weight bag as they pass by each other. Using a piece of denser iron will allow more room for the bags to go by each other. If I replace the bag with a barbell weight, there should be plenty of room.
I also thought about the scrap metal yard where I used to live. It had a sign that said “we buy scrap” and the local clowns used to paint over the S! They might have a piece of steel or iron for cheap. But how big of a piece of iron do I need? The gravity light instructions say to use up to 12 kilograms of rock in the heavy bag. That’s the same as 26.4 pounds, so I figured that 25 pounds was a good number to look for. 12 kilograms is the same as twelve thousand grams. I divided that by 7.85, which gave me 1528 cubic centimeters. I divided that by 2.54 cubed, because it’s a cube. My result was 93 cubic inches. A common thickness for steel is one inch, so I need 93 square inches of 1 inch thick steel. A 10 inch by 10 inch square would be a hundred square inches, so it’s slightly less than 10 inches square, or about nine and a half inches square. If it’s thicker, then it would be smaller than nine and a half inches square; 2 inches thick would be about 6.8 inches square.
So armed with that knowledge, I set off for a few stores to see if I could get a 25 pound barbell weight. I found nothing until I got to Walmart. There I found several different sized weights like 25 pounds, 10 pounds and 5 pounds. But the 25 pound weight was more than a dollar a pound, and the 10 pound weight wasn’t much cheaper. The five pound weights were nice and small and only cost $4 and change, so I bought 2 of those. But I still wasn’t happy. I pulled out my phone and got online to look for a scrap metal dealer. I found one in Anaheim, right down the street from Fry’s Electronics! Fry’s is the geek’s candy store here in California. All the high tech stuff: computers and computer parts and software and electronic parts and on and on and on. So I can kill two birds with one stone, so to speak. I hit Fry’s first because it was a little closer, but really since I’m a geek I wanted to go there first anyway. In the end I’m glad I did.
Fry’s was uneventful; they had some Sony Microvault 32 GB thumb drives on sale, but they were all gone. I think the employees buy all of the items on sale and then put them on eBay. So up the street I went and pulled into the scrap metal yard. I found some guy ordering the other workers around, so I talked to him and told him I was looking for a piece of iron about 25 pounds and the shape was not critical. He said I could have it for free and motioned to a guy to come over and said, Hey Carlos, Ve allí y buscar un blah blah blah blah. Soon Carlos was up on top of a scrap pile and threw down a piece of steel, so I went over. I picked it up; it was about an 8 inch by 11 inch piece of 1 inch thick steel. I thought it was about 85 to 90 square inches, and I said, That’s perfect, and thanked him and left. I got to the car and my hands were covered with rust and grime, so I had to take a piece of paper out of the trash and wipe my hands off. Well, I got to hit two places with at least partial success. I got home and washed the grime and rust off with the garden hose, then put the slab of steel on the scale. Was I surprised: 24-1/2 pounds! The scale doesn’t lie (unfortunately, sometimes). Almost right on the money! Later I filed off some of the rough edges and I got out the drill and found a sharp bit, and started drilling halfway along one edge. Really tough, so I got a bottle of paper shredder oil and lubricated the hole liberally. I proceeded slowly but surely; nothing like the smell of hot oil to get you motivated. Afterward, I put a screwdriver through the hole and picked it up, and it balanced perfectly. All I have to do is hang it on the Gravity Light with a short length of strong wire.