By Hamish Johnston

“A surprising amount of stuff gets wasted every year because consumers can’t get it out of the packaging it came in,” writes Katie Palmer, who covers the science beat at Wired. In her article “The physics behind those no-stick ketchup and mayo bottles”, she explains how the company LiquiGlide has developed its slippery coating for the insides of bottles. The challenge was to create a permanently wet coating that would stick to the inside of the bottle but not mix with the liquid foodstuff – and it also has to be safe for human consumption.

LiquiGlide spun out of the lab of Kripa Varanasi at the Massachusetts Institute of Technology and has just announced that an international food-packaging supplier will be using the coating on its mayonnaise bottles. You can watch a demonstration of the coating in the video above.

I am a Cub leader in my spare time and one of my favourite activities is the “trebuchet challenge”. Working in teams, the Cubs are given poles and rope that they lash together to make a medieval siege engine. The winner is the team whose trebuchet can lob a water balloon the farthest, although the balloons often get flung backwards and soak the Cubs.

There is a lot of interesting physics in a trebuchet – leverage, conservation of energy and more – so I hope that at least some of the Cubs will be inspired to go on to a career in physics. Over on medievalists.net, Danièle Cybulskie writes about the challenges of building a trebuchet and getting it to work properly. Her article is called “A good day for a trebuchet”.

This week’s Red Folder ends with some words of wisdom for aspiring science-fiction writers: “A science-fiction writer can often produce a more interesting story by strictly obeying the known laws of science than by blithely ignoring them.” That is the advice of physicist Robert Scherrer, who writes the Cosmic Yarns blog. Based at Vanderbilt University in the US, he offers this and other tips in the post “The speed of light in science fiction: when less is more”.

Scherrer recommends the short story “The Old Equations” by Jake Kerr – something to read this weekend if the weather is inclement where you are.