Corn starch and water are mixed in a plate to produce a goopy mixture
that can be scooped up and dribbled with a spoon. Inviting the students
to look closer, the professor suddenly slams his or her fist down on the
mixture, causing the students to jerk back - but the mixture doesn't
splatter; it momentarily becomes rock hard when acted on by a large
force. Another type of behavior is demonstrated by dragging a spoon
rapidly through the mixture to cause a ripping action.
Also available is "silly putty" which is hard and elastic under large
forces but flows under small forces. Mold it into a ball and bounce it,
and then leave on the lecture table; in ten or twenty minutes it will
flow out under gravity.
EmoticonEmoticon