'What is the slipperiest thing in the world?' asks 8 year old Evelyn? 'Why do my feet slip on a wet floor but when my feet are even slightly moist it's nearly impossible to put on a pair of socks without falling over and cursing the universe. What is going on here?' asks Evelyn's Dad, Sam. Hannah and Adam investigate the science of friction and lubrication - so called 'tribology' with the help of tribologists and mechanical engineers Professor Ashlie Martini from California University Merced and Professor Roger Lewis from the University of Sheffield. With their help Hannah and Adam find out why leaves on the line are so slippery, what happens to graphite in space and what is the slipperiest food. Professor of Materials, Mark Miodownik from University College London explains what's going on when friction stops two materials sliding past each other and wonders whether the slipperiest substance was actually discovered accidentally in a lab by scientists looking for something completely different. Also in the programme why the ability to reduce friction, even by minuscule amounts could have a huge impact for sustainability and reducing energy use. Producers: Jen Whyntie and Pamela Rutherford