ELI5 Pushback Tugs - why can't planes reverse on their own?

What’s the use of the cart that pushes back the airplane? Can planes not reverse without it? How can a cup of water not spill in an airplane when the plane tips its wings to make a broad turn? Why do military planes tend to have wings above the body and commercial planes have wings underneath the body? ... we explain like I'm five Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: runborgondy, ableseacat14, nil_defect_found, cow_launcher, tehwildman_, jonnycruz666, mak-15 and plane_pro To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Send us an e-mail: [email protected]