¿ìè¶ÌÊÓƵ

Cycling on hilly roads, what is the best option to save energy: go as fast as possible downhill to gain momentum for the next climb, or stop pedalling to have a rest and regain some strength?

Jean-Luc Kerdelhué,

Nantes, France

Is it feasible to start a fire with a fart and a static spark from human hair?

Jed Stephens,

via email

To answer this question – or ask a new one – email lastword@newscientist.com.

Questions should be scientific enquiries about everyday phenomena, and both questions and answers should be concise. We reserve the right to edit items for clarity and style. Please include a postal address, daytime telephone number and email address.

¿ìè¶ÌÊÓƵ retains total editorial control over the published content and reserves all rights to reuse question and answer material that has been submitted by readers in any medium or in any format.

Terms and conditions apply.