Description:
It's a Newton's Cradle with the design of a dog instead of just metallic balls. When you swing the tail, the head moves on the other side; and they can swing back and forth.
Principle:
It encompass the principle of the conservation of momentum and the conservation of energy.
Details:
The five swinging pieces will have equal masses. They will be mainly made of plastic but their contact points will be metallic (for better transfer of momentum). Each piece will be suspended with two equally long strings which made a V-shape. It will be a little bit more expensive than most toys since higher precision is required in constructing the pieces and the process of making the metallic contact points will be slight more costly. This is recommended for kids of age 7 or above, because it won't work if it's being tossed sideways.