Move the red dot on the trig function and the graph of the gradient function is shown below. Very neat! From Manipula Maths.
http://www.ies.co.jp/math/java/calc/sin_diff/sin_diff.html

This applet also shows the graph of the 2nd derivative.
http://www.ies.co.jp/math/java/calc/sin_2nd/sin_2nd.html