Why are four-person bobsleighs faster than two-person bobsleighs? Is it because they have two extra people pushing at the start and therefore are faster throughout their run or is it to do with weight and momentum? Surely there comes a point when the extra weight slows the bob too much? A few friends and I spent an hour or so arguing over this the other week, divided into those who thought it was the extra weight and others who thought it was the extra runners.

Alan Kane, Glasgow, UK

When I lift my wife for a good hug, her weight seems vastly different depending on whether she's limp or rigid. Is there anything real about the difference or is it my imagination that she seems much lighter (or certainly much easier to lift) when she's rigid? I noticed the same thing a few years back when I used to carry my kids to bed.

Geoff Patton, Wheaton, Maryland, US

I have a theory that may work in conjunction with popular belief that dinosaurs were wiped out by meteor impact. Given the size of animal and plant life during the time and to some the seemingly laughable proportions ie huge bodies and small legs arms of some creatures. If gravitational strength was lower those creatures would not need strength in proportion to body mass or wieght.  Plants would/could grow larger taller without the confines of gravity as we know it. Could it also explain the seemingly impossible feats of strenth we debate over regarding placement of objects and the building of structures by our human ancestors. Scientists research and tell us of THE meteor impact that wiped out the dinosaurs. Could it be that over a period of time there was more than a couple of impacts that we can no longer find evidence of and that, and by changing the density and mass of the earth we now experience gravity at a higher strength. We know that physically we adapt ie loss of hair due to temperature change, creatures in caves being blind etc.