What are stiff, flexible, ductile, and brittle? 什麼是硬度、彈性、延展性、和脆性？

Music: www.bensound.com
Reference:
www.materials.unsw.edu.au/stu...
mse.engin.umich.edu/internal/...
sciencing.com/properties-uses...
www.benedict-miller.com/news-...
www.thoughtco.com/what-are-ex...
amesweb.info/Materials/Youngs...
www.commonwealthplywood.info/...