@article{aguirregabiria_hernández_rivas_2007, 
  title={Falling elastic bars and springs}, 
  volume={75}, 
  DOI={10.1119/1.2733680}, 
  publisher={American Association of Physics Teachers (AAPT)}, 
  author={Aguirregabiria and Hernández and Rivas}, 
  year={2007}
  }