A motor can be used as a generator.
For this motor it is necessary to gear up by a factor
of 25.
.
A motor used to generate electricity is also
called a dynamo.
Back view
Alternate building idea on http://netapps.marshall.edu/lego/dc/03Ap02LEGOLANDeLAB/EnergyLEGOLAND.html
Build the car with pulley drive
or chain drive.
To connect the motor to the axle with the bevelled gear
use chain links around the 16 tooth and 24 tooth gear.
Connect the lead wire to the motor and the generator
and turn the handle.
How fast must your turn to get the car started?
Is it easier to keep the car moving than to start it?
Make the ramp by putting two 2 by 4 blocks together at one
side of the green plate and turning it upside down.
Place the car so that it is exactly even with the edge and let go.
Can you make the car go down the ramp?
Can it go up?
http://netapps.marshall.edu/lego/lessonplans/Generate/generator.htm
eLab projects use motors as generators.
See some examples on http://netapps.marshall.edu/lego/Miller/MillerMM2001groups14.html