In the UK, one penny coins are only legal tender for amounts up to 20p. (Source: Royal Mint)
Wednesday, 13 May 2015
Tuesday, 21 April 2015
You may have lived for field trips as a kid, looking forward to a whole day of out-of-school fun and exploring. That is, until you got started on a tour of some musty building that seemed, well, boring. Not even the tour guide's explanation of how the glass in the wavy, uneven windowpanes has slowly flowed downward over time could keep your attention.
Liquid windowpanes? No.
Rather than the (magical-sounding) slow drip of centuries, the reason old glass windows aren't perfectly even and clear is because of how they were made. Until the early-mid 1800s, most window glass was made using a process called the crown method. The glass was blown, flattened, heated and spun, yielding a sheet that was relatively cheap to produce. It was also rippled and thicker in some places than in others.
In other words, the windows looked that way when they were installed, and they look that way now. No downhill liquid flow is involved. (And if you're really wondering: Glass is an amorphous solid.
Monday, 13 April 2015
This is a myth that originates before we had spaceflight, so no-one knew enough to get it debunked before it became so pervasive. In fact, you can see other man-made objects from space (especially when the part of the Earth being viewed is awash in the artificially illuminated glow of nighttime). It's also pretty hard to pick out the Great Wall of China from any space-based locale. In low-Earth orbit, it's next to impossible to see it with the naked eye. Even with a fairly hefty camera lens, it's still challenging to tell if you're looking at the Great Wall or not.