Cycling UK Forum

"Inside Britain's biggest sewer under London's River Thames":
https://www.bbc.co.uk/news/av/science-e ... t-65091803

Today's physics question: How fast would you have to go for a full loop?

Jonathan

The minimum speed would be where the centrifugal force given by mv^2/r (m=mass, v= speed, r is radius) balances the weight given by mg (g is acceleration due to gravity)

Rearranging the min speed vmin = sqrt(gr)

Taking the radius as 2.5m snd g=9.8m/s2 gives 4.9m/s or 18km/hr.

Would need to be faster than that to maintain grip at the top of the loop.

Actually it's a bit more - around 5.4 m/s (~19.5 kph), since the radius is 3.5 m rather than 2.5. The problem would be accelerating to that speed in the space available, but assuming you could do it the effect on the body could be interesting since your head would experience a smaller radial acceleration than your legs and feet, so that there'd be less oxygen keeping your brain awake. Could be you'd be unconscious and unaware of the eventual crash to the floor when you stop pedalling. You'd be better off on a recumbent.

Maybe Colin Furz could be persuaded try it.

Wouldn't the contents of the sewer reduce the coefficient of friction somewhat? May need to be putting out far greater power than expected to get up to speed.

Many years ago I watched a brilliant documentary about Sir Joseph Bazalgette...fascinating stuff. Some years later I interrupted a romantic walk along London's embankment with my wife, and started rattling on about the huge sewer under our feet, and the genius who built it. Without pause she asked 'Do you mean him?'..unbeknownst to me we had stopped at the exact spot of the Bazalgette monument.
Perfect timing, although my enthusiasm for a Victorian poo maestro took the edge off the romance somewhat...