PHY 1010U Lecture Notes - Lecture 9: Free Body Diagram, Chris Hadfield, Friction
Document Summary
Question: why bother and push a box, if pushing results in the box pushing back. Question: a falling ball falls towards earth due to earth"s pulling force on it. Is the earth being pulled upwards by the ball as well: yes, no. Propulsion is the force that an object with an internal source of energy uses to push itself forward. It can be static friction or thrust forces pointing always in the forward direction. Examples of propulsion: fs on surface fs on person fs on surface fs on person fplane on gases. In analyzing a problem we divide the interacting objects into the system and the environment. The system consists of the objects whose motion we are studying (person and crate in example below). We determine all the action-reaction pairs of forces between those objects. The environment consists of all external object (earth and floor) that interact with the system. We determine those external forces on the systems objects.
