"cjcampbell" wrote in message
oups.com...
If the car's airspeed indicator said 60 then the speedometer will
indicate 120. But the car would then need to expend the same energy to
accelerate to 60 as it would to accelerate to 120 on a stationary road.

No, not really. Most of the horsepower of a car is used to counteract
aerodynamic drag, at that speed. Unless the treadmill (conveyor belt,
whatever) somehow gets the air above it to move rearward along with the
belt, the car barely has to use more power than it would accelerating to,
and cruising at, 60 mph on a regular road. It absolutely doesn't require
anywhere near as much power as it would to travel at 120 mph on a regular
road.

Pete