1. NET FORCE

2. Definitions of Force Force is a push or a pull acting on an object.
Force is a vector (magnitude & direction)

3. More on Force… Forces can change the motion of an object
SI unit = newton (N)
Net force is the vector sum of all forces acting on an object.
Since force is a vector, the net force will have magnitude and direction.

4. FREE BODY DIAGRAM
We will draw what is called a free body diagram to show forces acting on the object
Draw the object as a box
Draw all forces acting on it with arrows coming out of the box in the direction they act

5. More on Net Force Forces in same direction: add
Net force in same direction as forces.
See picture 2
Forces in opposite directions: subtract. Net force in direction
of larger force.
See picture 3
Equal forces in opposite directions : subtract. Net force is zero
See picture 1

6. What is the net force acting on each object below?

7. Balanced forces Net force = 0
Balanced forces do NOT cause any change in an object’s motion.

8. Balanced forces

9. Unbalanced force Net force ≠ zero
Causes an object to change its motion
Many unbalanced forces causing motion: video

10. Example
Two tugboats are moving a barge. Tugboat A exerts a force of 3000 Newtons on the barge. Tugboat B exerts a force of Newtons in the same direction. What is the combined force on the barge?
Draw arrows showing the individual and combined forces of the tugboats.

11. Example
Now suppose that Tugboat A exerts a force of 2000 Newtons on the barge and Tugboat B exerts a force of 4000 Newtons in the opposite direction. What is the combined force on the barge?
Draw arrows showing the individual and combined forces of the tugboats.

12. Example
Could there ever be a case when Tugboat A and Tugboat B are both exerting a force on the barge but the barge doesn't move? Draw arrows showing the individual and combined forces in such a situation.