text: help!!!! dont understand! all teachers maybe??? i have my science presntation on toys on tuesday and the question is: to bring in a toy that operates on scientific principles. i must explain these principles. however im not too sure is it asking me to explain how i would use that toy maybe a yo yo? in a science lesson?  thnk you!!! the yo yo is a good idea, there is the force of gravity, friction, inertia, among others, gravity can pull it down or you can throw it down, friction of the rope to either keep the yo yo at the end of the string or to bring it back up, same with inertia. good luck