When two ________________ are rubbed together, the resistance is called _______________. This definition was stated by an engineer helping to drill a _______________ through metal about two hundred years ago.
The dancing movement of popping popcorn is said to be __________________ or unorganized. This type of motion was described nearly two hundred years ago by Robert Brown while he observed tiny yellow, grains of flower_______________ floating on water. We now call this movement _________________ Motion.
What caused the movement observed by Robert Brown? We now know that water is composed of tiny, unseen ____________________ that are in constant, vibrating ________________. Any tiny specks in the water move due to __________________.
