Â鶹´«Ã½

A cyclist saves energy by staying in the slipstream of the rider in front. But does the rider in front expend more energy than a solo rider travelling at the same speed?

Paul Fairfield,

Bebington, Merseyside, UK

If Earth stopped rotating, would this affect the force of gravity?

Lyn Williams,

Neath, Port Talbot, UK

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…