Previously there was some discussion of various low-tech
schemes for measuring the power involved in pedaling a bicycle.
Now let's look at it from another angle, not as a simple
9th-grade demo but rather as high-tech real-world physics as
used by professional and semi-pro bike racers. There is a
nice connection here between physics, physiology, and phys ed.
There are a number of fancy bike power meters available.
They all measure and record torque times rate of rotation.
a) Some measure torque at the pedal spindle.
b) Some measure torque at the crank arm.
c) Some measure torque at the spider.
d) Some measure torque at the rear hub.
(a) and (b) are nice because they give separate readings
for right leg and left leg.
Also
-- Some measure cadence using magnets plus a pickup
coil (or Hall effect sensor).
-- Some measure cadence using MEMS accelerometers.
Power meters are sufficiently expensive that they are not
generally found on the bikes that students ride around campus
... but they are heavily used by competitive racers.