I like to move back and forth on black sock went i am wiggled
the particles in a surface water move back- and- forth only.
the particles in a surface water move back- and- forth only.
After you stroke a tuning fork, all the particles move back and forth. If you play a piano, particles of the wire move back and forth.
solids
it moves its body back and forth
solid
back and forth?
solid
To move quickly back and forth.
solids
solids
move back and forth in a circuit. :)