Journal Entry 2/1

1. You are seated on a bench. The earth exerts a force on you, and the bench exerts a force on you. Do these two forces represent a Newton’s Third Law force pair? Explain.

The earth is exerting a downward force on me, trying to pull me down. The bench on the other hand is exerting an upward force on me, pushing me up. I am not moving which means that there is no unbalanced force on me. Because these forces are opposite and equal, they represent a Newton's Third Law force pair.

2. A pen sits on a desk. The desk exerts a force on the pen, and the pen exerts a force on the desk. Do these two forces represent a Newton’s Third Law force pair? Explain.

The desk is exerting an upward force on the pen, pushing it up. The pen is exerting a downward force on the desk, pushing it down. Again, nothing is moving so there is no unbalanced force in this scenario. Therefore the forces are opposite and equal and represent a Newton's Third force pair.

3. You pull on a rope. The rope pulls on a wagon. Do these two forces represent a Newton’s Third Law force pair? Explain.

If my pull on the rope is to the left, I am exerting a force to the left. Because of me, when the rope pulls on the wagon it will also be exerting a force to the left. Although the forces may be equal, they are not in opposite directions. They cannot be a force pair for Newton's Third Law.

4. A book slides across a tabletop. The book exerts a downward force on the table, and the table exerts a frictional force on the book opposite the direction of its motion. Do these two forces represent a Newton’s Third Law force pair? Explain.

Although there are two forces here, the book's downward force on the table and the frictional force of the table on the book, they do not correlate because one is a vertical force and the other is a horizontal force. Also, because the book is sliding across the tabletop, there is an unbalanced force. Therefore, this is not a force pair of Newton's Third Law.