I agree that it would not require much more additional power to overcome the
additional friction drag of wheels spinning at twice the normal speed but it
is not zero.


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Travis
"cjcampbell" wrote in message
oups.com...

Tony wrote:
If the car had an airspeed indicator it would, I agree, indicate 60. In
the model I suggested the car is moving to the north at 60, the
treadmill to the south at 60, and the speedometer will indicate 120.

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.

An aircraft would need no additional power to accelerate to 60 on a
treadmill.