1. Balanced vs. Unbalanced Forces
October 25, 2017
Balanced vs. Unbalanced Forces

2. Drill – Take out Lab Handout
The term “net” is used in common language, such as “net pay”, “net worth”, “net profit”, or “net weight”. What does “net” mean in these cases?
Based on what you said above, what do you think the term “net force” means?

3. Newton’s First Law of Motion
Newton’s first law of motion is also called the law of inertia.
Law of inertia states that an object at rest will remain at rest or an object in motion will continue moving at constant velocity unless acted upon by an unbalanced force.

4. Inertia
Property of matter that causes it to resist change in its state of motion.
Mass is the measure of an object’s inertia.
More massive objects have more inertia than less massive objects.

5. Newton’s First Law of Motion

6. Demonstration – Hammer + Textbooks
Due to the large mass of the books, the force of the hammer is sufficiently resisted (inertia).
This is demonstrated by the fact that the teacher does not feel the hammer blow.

7. Balanced vs. Unbalanced Forces
What happened to the file cabinet in Part B of the lab? (Applied Force = 200 N, Friction = -200 N).
Newton’s First Law: file cabinet at rest remained at rest…
Because it was not acted upon by an UNBALANCED FORCE…
NET FORCE = ZERO
If object in motion when NET FORCE = zero, then object will remain in motion at a CONSTANT VELOCITY

8. Balanced vs. Unbalanced Forces
Balanced Forces = positive forces acting on object are EQUAL to the negative forces; the net force is zero.
Unbalanced Forces = the positive forces do NOT EQUAL the negative forces; the net force is not zero.

9. Are these forces balanced? (Fnet = 0)

10. Are these forces balanced? (Fnet = 0)

11. Are these forces balanced? (Fnet = 0)

12. Are these forces balanced? (Fnet = 0)

13. True or False
If the forces acting on an object are balanced then the object MUST be at rest.
FALSE!!! Newton’s First Law = Law of Inertia. Tells us that “an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.”
Objects tend to "keep on doing what they're doing" (unless acted upon by an unbalanced force)