This is an engaging way, adapted from Elsa Findlay's masterpiece "Rhythm and Movement - Application of Dalcroze Eurhythmics" to teach the Dynamics Piano and Forte.
Divide the class into two groups, first group are the 'grumpy birds' and the others are sneaky and 'declawed' kitty cats hiding in the bushes. You can make it even more engaging by pretending you are looking for your lost cats. The cats sneak up on the birds (I often use a diminished 7 chord, played piano/soft and I adapted the 'forte music' for the grumpy birds from Widor's V finale/Toccata for organ. Switch parts; birds get a chance at being a cat and the cats may be the birds etc.... always finish by identifying who was forte and who was piano.
(I usually use both hands at the piano, but I had to hold the camera too!)
You may find more ideas at:
sites.google.com/site/eurhythmicfritz/subjects-and-lessons/original-lessons/dynamics-1