The external work done on an elastic member in causing it to distort
from its unstressed state
is transformed into strain energy which is a form of potential energy.
The strain energy in the form of elastic deformation is mostly recoverable in the form of mechanical work."
Use the energy stored as strain energy in a rubber band.
Inertia is going to be a help with this project.
After some building and changing they were able to get a car to go the full width of the room.
The recorded lengths generally increased showing that they were making improvements.
With longer cars the rubber bands were stretched farther.
The band needed to come free of the car with out catching in the wheels.