By Hamish Johnston
In the above video Brian Anderson of Brigham Young University shows how the acoustic concept of “time reversal” can be used to knock over a series of LEGO figures using sound. The idea is that sound waves are broadcast into an environment and captured by a sensor at a specific location. The signal is then used to work-out how the sound waves bounced about before reaching the location and this information is then used to target that specific location with subsequent sound waves. In the demonstration, sound knocks over 29 LEGO figures one-by-one. It’s very impressive and entertaining as well.
When I was a boy in the 1970s and health and safety was embryonic at best, we used to make what we called a “Murphy’s cannon”. This was three or four tins taped together to make a tube that was sealed at one end. We would put a little lighter fluid through a small hole at the sealed end, drop in a tennis ball and ignite the fluid. With a whoosh, the tennis ball would fly high over the house, much to our delight. Little did we know that our creation (a type of “potato cannon”) was first developed by the British in the Second World War as a low-cost way of launching grenades from ships. Called Holman Projectors, the devices were powered by steam rather than combustion. They bear a closer resemblance to compressed-air powered potato cannons than our Murphy’s cannon, as William Gurstelle explains in Popular Mechanics.
Do your political beliefs affect your taste in popular science book? Yes, according to a study of millions of online book purchases. Michael Macy, James Evans and colleagues found that people who bought books that suggest they have liberal views tended to prefer books on basic sciences, such as physics and astronomy. People whose book-buying suggests they have conservative views preferred books on applied sciences, like criminology and geophysics. The researchers say that their findings back-up the idea that people tend to exist in ideological echo chambers or information bubbles that reinforce their established views.