Assertion: piano's hammer | /r/HasProperty | covered with dense wool
Facets:
Source sentences:
text: (Modern hammers are covered with dense wool felt; some early pianos used leather.)
text: The piano is an acoustic, stringed musical instrument invented in Italy by Bartolomeo Cristofori around the year 1700 (the exact year is uncertain), in which the strings are struck by wooden hammers that are coated with a softer material (modern hammers are covered with dense wool felt; some early pianos used leather).