Videre non videri
Join Date: Sep 2004
Location: Gothenburg, Sweden
Posts: 3,208
Bikes: 1 road bike (simple, light), 1 TT bike (could be more aero, could be lighter), 1 all-weather commuter and winter bike, 1 Monark 828E ergometer indoor bike
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If they were both riding on the moon, we can disregard the atmosphere (although the moon technically has one, it's so feeble that it's completely negligible).
Then, all that is left is internal friction and rolling resistance.
Both increase pretty much linearly with speed, so if a rider moves twice as fast, he will need to exert twice the power.
However, double the speed, and you only have to travel for half the time. So, if the slower rider pushes 100 W going 25 mph for one hour, he will have used 0.1 kWh (100 W = 0.1 kW, and one hour makes it into kWh) of energy to overcome the mechanical resistance. And about 0.5 kWh in total, since the body has an efficiency of about 20% when cycling.
The faster rider pushes 200 W for a speed of 50 mph, but reaches the destination in only half an hour. He too has only used up 0.1 kWh, or 0.5 kWh in total.
Imagine then what vacuum tunnels could do for train travel!