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Old 08-09-16 | 03:18 PM
  #80  
FBinNY
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Joined: Apr 2009
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From: New Rochelle, NY

Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter

Originally Posted by McBTC
We may need a physics check. I believe it takes more energy to move a given object more quickly. Lance Armstrong had to calculate how much energy it would take to raise his body and bike weight to the to finish line at Alp D'Huez but he also had to include how much more energy it would take to be at that line sooner than Jan Ullrich.
Yes and No.

In air (or any fluid) speed is energy expensive because resistance increases proportional to the square of speed. So you get 4 times the resistance riding at twice the speed. Which is why they promote driving 55 vs 65 to save gas.

OTOH - the work done climbing is purely a function of weight and height gained. Speed isn't a factor in work, so fast or slow,the energy used is the same. OTOH - doing the same work in less time requires more POWER, which is something different. Faster riders of the same weight are more powerful, but the energy they consume doing the same task is the same.

Quickie glossary.

Force is what's needed to move a load against resistance (or accelerate it if no resistance).
Work is the product of Force X the distance moved. Energy used is the work done x the efficiency rating.
Power is the work done per time unit, so those who can work faster are more powerful.
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Last edited by FBinNY; 08-09-16 at 04:49 PM.
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