Balanced Forces Particle Model

Balanced Forces on the Hudson

©Mark Schober
In the photo, a tugboat pushes a barge up the Hudson River. What does the force diagram for the tugboat look like? How does the force the tugboat exerts on the barge compare to the force the barge exerts on the tugboat? How can such a small boat push a barge in front of it that might weigh 50 times as much as the boat?